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Bohr Model of the Atom

The Bohr model or Rutherford-Bohr model of the atom is a cake or planetary model that describes the structure of atoms mainly in terms of quantum theory. It’s called a planetary or cake model because electrons orbit the atomic nucleus like planets orbit the Sun, while the circular electron orbits form shells, like the layers of a cake. Danish physicist Niels Bohr proposed the model in 1913.

The Bohr model was the first atomic model incorporating some quantum mechanics. Earlier models were the cubic model (1902), plum-pudding model (1904), Saturnian model (1904), and Rutherford model (1911). Ultimately, models based entirely on quantum mechanics replaced the Bohr model. Yet, it’s an important model because it describes the quantum behavior of electrons in simple terms and explains the Rydberg formula for the spectral emission lines of hydrogen.

Key Points of the Bohr Model

• The atomic nucleus consists of protons and neutrons and has a net positive charge.
• Electrons have a negative charge and orbit the nucleus.
• Electron orbits are circular, but not all electrons orbit in the same plane (like planets around a star), resulting in spheres or shells where an electron might be found. While gravity determines orbits of planets around stars, electrostatic forces (Coulomb force) causes electrons to orbit the nucleus .
• The lowest energy for an electron (most stable state) is in the smallest orbit, which is closest to the nucleus.
• When an electron moves from one orbit to another, energy is absorbed (moving from lower to higher orbit) or emitted (moving from higher to lower orbit).

The Bohr Model of Hydrogen

The simplest example of the Bohr Model is for the hydrogen atom (Z = 1) or for a hydrogen-like ion (Z > 1), in which a negatively charged electron orbits a small positively charged nucleus. According to the model, electrons only occupy certain orbits. The radius of possible orbits increases as a function of n 2 , where n is the principle quantum number. If an electron moves from one orbit to another, energy is absorbed or emitted. The 3 → 2 transition produces the first line of the Balmer series. For hydrogen (Z = 1), this line consists of photons with a wavelength of 656 nm (red).

Bohr Model for Heavier Atoms

The hydrogen atom only contains one proton, while heavier atoms contain more protons. Atoms require additional electrons to cancel out the positive charge of multiple protons. According to the Bohr model, each orbit only holds a certain number of electrons. When the level filled, additional electrons occupy the next higher level. So, the Bohr model for heavier electrons introduces electron shells. This explains some properties of heavy atoms, such as why atoms get smaller as you move from left to right across a period (row) of the periodic table, even though they contain more protons and electrons. The model also explains why noble gases are inert, why atoms on the left side of the periodic table attract electrons, and why elements on the right side (except noble gases) lose electrons.

One problem applying the Bohr model to heavier atoms is that the model assumes electron shells don’t interact. So, the model doesn’t explain why electrons don’t stack in a regular manner.

Problems With the Bohr Model

While the Bohr model surpassed earlier models and described absorption and emission spectra, it had some issues:

• The model couldn’t predict spectra of large atoms.
• It doesn’t explain the Zeeman effect.
• It doesn’t predict relative intensities of spectral lines.
• The model violates the Heisenberg Uncertainty Principle because it defines both the radius and orbit of electrons.
• It incorrectly calculates ground state angular momentum. According to the Bohr model, ground state angular momentum is L = ħ . Experimental data shows L=0.
• The Bohr model doesn’t explain fine and hyperfine structure of spectral lines.

Improvements to the Bohr Model

The Sommerfeld or Bohr-Sommerfeld model significantly improved on the original Bohr model by describing elliptical electron orbits rather than circular orbits. This allowed the Sommerfeld model to explain atomic effects, such as the Stark effect in spectral line splitting. However, the Sommerfeld model couldn’t accommodate the magnetic quantum number.

In 1925, Wolfgang’s Pauli’s atomic model replaced the Bohr model and those based upon it. Pauli’s model was based purely on quantum mechanics, so it explained more phenomena than the Bohr model. In 1926, Erwin Schrodinger’s equation introduced wave mechanics, leading to the modifications of Pauli’s model that are used today.

• Bohr, Niels (1913). “On the Constitution of Atoms and Molecules, Part I”.  Philosophical Magazine . 26 (151): 1–24. doi: 10.1080/14786441308634955
• Bohr, Niels (1914). “The spectra of helium and hydrogen”.  Nature . 92 (2295): 231–232. doi: 10.1038/092231d0
• Lakhtakia, Akhlesh; Salpeter, Edwin E. (1996). “Models and Modelers of Hydrogen”.  American Journal of Physics . 65 (9): 933. Bibcode:1997AmJPh..65..933L. doi: 10.1119/1.18691
• Pauling, Linus (1970). “Chapter 5-1”.  General Chemistry  (3rd ed.). San Francisco: W.H. Freeman & Co. ISBN 0-486-65622-5.

Related Posts

Bohr Model of the Atom Explained

Planetary Model of the Hydrogen Atom

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The Bohr Model has an atom consisting of a small, positively charged nucleus orbited by negatively charged electrons. Here's a closer look at this planetary model.

Overview of the Bohr Model

Niels Bohr proposed the Bohr Model of the Atom in 1915. Because the Bohr Model is a modification of the earlier Rutherford Model, some people call Bohr's Model the Rutherford-Bohr Model. The modern model of the atom is based on quantum mechanics. The Bohr Model contains some errors, but it is important because it describes most of the accepted features of atomic theory without all of the high-level math of the modern version. Unlike earlier models, the Bohr Model explains the Rydberg formula for the spectral emission lines of atomic hydrogen .

The Bohr Model is a planetary model in which the negatively charged electrons orbit a small, positively charged nucleus similar to the planets orbiting the sun (except that the orbits are not planar). The gravitational force of the solar system is mathematically akin to the Coulomb (electrical) force between the positively charged nucleus and the negatively charged electrons.

Main Points of the Bohr Model

• Electrons orbit the nucleus in orbits that have a set size and energy.
• The energy of the orbit is related to its size. The lowest energy is found in the smallest orbit.
• Radiation is absorbed or emitted when an electron moves from one orbit to another.

Bohr Model of Hydrogen

The simplest example of the Bohr Model is for the hydrogen atom (Z = 1) or for a hydrogen-like ion (Z > 1), in which a negatively charged electron orbits a small positively charged nucleus. Electromagnetic energy will be absorbed or emitted if an electron moves from one orbit to another. Only certain electron orbits are permitted. The radius of the possible orbits increases as n 2 , where n is the principal quantum number . The 3 → 2 transition produces the first line of the Balmer series . For hydrogen (Z = 1) this produces a photon having wavelength 656 nm (red light).

Bohr Model for Heavier Atoms

Heavier atoms contain more protons in the nucleus than the hydrogen atom. More electrons were required to cancel out the positive charge of all of the protons. Bohr believed each electron orbit could only hold a set number of electrons. Once the level was full, additional electrons would be bumped up to the next level. Thus, the Bohr model for heavier atoms described electron shells. The model explained some of the atomic properties of heavier atoms, which had never been reproduced before. For example, the shell model explained why atoms got smaller moving across a period (row) of the periodic table, even though they had more protons and electrons. It also explained why the noble gases were inert and why atoms on the left side of the periodic table attract electrons, while those on the right side lose them. However, the model assumed electrons in the shells didn't interact with each other and couldn't explain why electrons seemed to stack irregularly.

Problems With the Bohr Model

• It violates the Heisenberg Uncertainty Principle because it considers electrons to have both a known radius and orbit.
• The Bohr Model provides an incorrect value for the ground state orbital angular momentum .
• It makes poor predictions regarding the spectra of larger atoms.
• The Bohr Model does not predict the relative intensities of spectral lines.
• It does not explain fine structure and hyperfine structure in spectral lines.
• The Bohr Model does not explain the Zeeman Effect.

Refinements and Improvements to the Bohr Model

The most prominent refinement to the Bohr model was the Sommerfeld model, which is sometimes called the Bohr-Sommerfeld model. In this model, electrons travel in elliptical orbits around the nucleus rather than in circular orbits. The Sommerfeld model was better at explaining atomic spectral effects, such the Stark effect in spectral line splitting. However, the model couldn't accommodate the magnetic quantum number.

Ultimately, the Bohr model and models based upon it were replaced Wolfgang Pauli's model based on quantum mechanics in 1925. That model was improved to produce the modern model, introduced by Erwin Schrodinger in 1926. Today, the behavior of the hydrogen atom is explained using wave mechanics to describe atomic orbitals.

• Lakhtakia, Akhlesh; Salpeter, Edwin E. (1996). "Models and Modelers of Hydrogen". American Journal of Physics . 65 (9): 933. Bibcode:1997AmJPh..65..933L. doi: 10.1119/1.18691
• Linus Carl Pauling (1970). "Chapter 5-1".  General Chemistry  (3rd ed.). San Francisco: W.H. Freeman & Co. ISBN 0-486-65622-5.
• Niels Bohr (1913). "On the Constitution of Atoms and Molecules, Part I" (PDF). Philosophical Magazine . 26 (151): 1–24. doi: 10.1080/14786441308634955
• Niels Bohr (1914). "The spectra of helium and hydrogen". Nature . 92 (2295): 231–232. doi:10.1038/092231d0
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CERN Accelerating science

Atomic flashback: A century of the Bohr model

In July 1913, Niels Bohr published the first of a series of three papers introducing his model of the atom

12 July, 2013

By Kelly Izlar

Niels Bohr, a founding member of CERN, signs the inauguration of the Proton Synchrotron on 5 February 1960. On the right are François de Rose and then Director-General Cornelius Jan Bakker (Image: CERN)

The most instantly recognizable image of an atom resembles a miniature solar system with the concentric electron paths forming the planetary orbits and the nucleus at the centre like the sun. In July of 1913, Danish physicist Niels Bohr published the first of a series of three papers introducing this model of the atom, which became known simply as the Bohr atom.

Bohr, one of the pioneers of quantum theory, had taken the atomic model presented a few years earlier by physicist Ernest Rutherford and given it a quantum twist.

Rutherford had made the startling discovery that most of the atom is empty space. The vast majority of its mass is located in a positively charged central nucleus, which is 10,000 times smaller than the atom itself. The dense nucleus is surrounded by a swarm of tiny, negatively charged electrons.

Bohr, who worked for a key period in 1912 in Rutherford’s laboratory in Manchester in the UK, was worried about a few inconsistencies in this model. According to the rules of classical physics, the electrons would eventually spiral down into the nucleus, causing the atom to collapse. Rutherford’s model didn’t account for the stability of atoms, so Bohr turned to the burgeoning field of quantum physics, which deals with the microscopic scale, for answers.

Bohr suggested that instead of buzzing randomly around the nucleus, electrons inhabit orbits situated at a fixed distance away from the nucleus. In this picture, each orbit is associated with a particular energy, and the electron can change orbit by emitting or absorbing energy in discrete chunks (called quanta). In this way, Bohr was able to explain the spectrum of light emitted (or absorbed) by hydrogen, the simplest of all atoms.

Bohr published these ideas in 1913 and over the next decade developed the theory with others to try to explain more complex atoms. In 1922 he was rewarded with the Nobel prize in physics for his work.

However, the model was misleading in several ways and ultimately destined for failure. The maturing field of quantum mechanics revealed that it was impossible to know an electron’s position and velocity simultaneously. Bohr’s well-defined orbits were replaced with probability “clouds” where an electron is likely to be.

But the model paved the way for many scientific advances. All experiments investigating atomic structure - including some at CERN, like those on antihydrogen and other exotic atoms at the Antiproton Decelerator , and at the On-Line Isotope Mass Separator ( ISOLDE) - can be traced back to the revolution in atomic theory that Rutherford and Bohr began a century ago.

"All of atomic and subatomic physics has built on the legacy of these distinguished gentlemen," says University of Liverpool’s Peter Butler who works on ISOLDE. 

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Bohr's Model

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Niels Bohr [1]

In 1913, the physicist Niels Bohr introduced a model of the atom that contributed a greater understanding to its structure and quantum mechanics. Atoms are the basic units of chemical elements and were once believed to be the smallest indivisible structures of matter.

The concept and terminology of the atom date as far back as ancient Greece, and different models were proposed and refined over time. The most famous are attributed to John Dalton , J.J.Thompson and Ernest Rutherford .

Each atomic model has contributed to a deeper understanding of the behavior of atoms and subatomic particles . The Bohr model was the first to propose quantum energy levels, where electrons orbit the nucleus at predefined distances and must overcome an energy barrier to move into a new orbital . Bohr was awarded a Nobel prize in 1922 for his investigations into atomic structure.

Bohr's Atomic Theory

Drawbacks of bohr's atomic theory, radius of bohr's orbit, energy of bohr's orbit, velocity of an electron in bohr's orbit, orbital frequency or rotations per second, time period of an electron in bohr's orbit.

The key difference between Bohr's atomic model and earlier atomic models is that the electron can only move around the nucleus in orbits of specific, allowed radii . Another way to phrase this is to say that the electron can only occupy certain regions of space.

Bohr postulated the following regarding atomic structure:

The electrons revolve around the nucleus in special orbits called discrete orbits to overcome the loss of energy. When an electron revolves around the nucleus in this orbit, it does not radiate energy. This proved that the electrons need not lose energy and fall into the nucleus.

Each orbit is called a shell or energy level, and each level contains a specific amount of energy . The Rutherford–Bohr model of a hydrogen atom, where the negative electron is confined to an atomic shell, encircles a positively charged nucleus and where an electron jump between orbits (from \(n=3\) to \(n=2\)) emits or absorbs an amount of electromagnetic energy (\(hf\)).[1] The 3 → 2 jump here is the first line of the Balmer series , and for hydrogen (Z = 1) it emits a photon of wavelength 656 nm (red light). [2]

An electron will absorb energy when moving from a lower energy level to a higher energy level. This is called an excited state .

An electron will radiate energy when moving from a higher energy level to a lower energy level.

When electrons move from one orbit to another, they emit photons, producing light in characteristic absorption and emission spectra . Since each element has its own signature, the spectra can be used to determine the composition of a material. This principle has been harnessed in many types of spectroscopy . Emission spectra are also responsible for the colors seen in neon signs and fireworks .

Orbits closer to the nucleus (those that have lower energy levels) are more stable. (An electron in its orbit with the lowest possible energy is said to be in its ground state .)

Out of the infinite number of possible circular orbitals around the nucleus, the electron can revolve only in those orbits whose angular momentum is an integral multiple of \(\frac h{2\pi}\), i.e. angular momentum is quantized and \(mvr = \frac{nh}{2\pi},\) where \(m\) = mass of an electron, \(v\) = velocity of an electron, \(r\) = radius of the orbit, and \(n\) = number of the orbit.

Bohr's model only explains the spectra of species that have a single electron, such as the hydrogen atom \((\ce{H})\), \( \ce{He+, Li^2+, Be^3+,} \) etc.

Bohr's theory predicts the origin of only one spectral line from an electron between any two given energy states. Under a spectroscope of strong resolution, a single line is found to split into a number of very closely related lines. Bohr's theory could not explain this multiple or fine structure of spectral lines. The appearance of the several lines implies that there are several sub energy levels of nearly similar energy for each principal quantum number , n . This necessitates the existence of new quantum numbers.

It does not explain the splitting of spectral lines under the influence of a magnetic field (the Zeeman effect ) or under the influence of an electric field (the Stark effect ).

The pictorial concept of electrons jumping from one orbit to another orbit is not justified because of the uncertainty in their positions and velocities.

The force of attraction between the electron and proton for an atom with atomic number \(Z\) is

\[\begin{align} F_A=\text K\dfrac{q_1q_2}{r^2}=\text K\dfrac{(Ze)(-e)}{r^2}=-\text K\dfrac{Ze^2}{r^2}.\end{align}\]

And the centrifugal force is given by

\[F_C =-\dfrac{mv^2}{r}.\]

But the force of attraction is equal to the centrifugal force, so

\[\begin{align} \text- K\dfrac{Ze^2}{r^2}&=-\dfrac{mv^2}{r}\\\\ v^2&=\text K\dfrac{Ze^2}{mr}. \end{align}\]

But from Bohr's theory

\[\begin{align} mvr =\dfrac{nh}{2\pi}\implies v&=\dfrac{nh}{2\pi m r}\\\\ v^2&=\dfrac{n^2h^2}{4\pi^2 m^2 r^2}. \end{align}\]

Equating both the results for \(v^2\) gives

\[\begin{align} \text K\dfrac{Ze^2}{Mr}&=\dfrac{n^2h^2}{4\pi m^2r^2}\\\\ \Rightarrow r&=\dfrac{n^2h^2}{4\pi^2 m\text KZe^2}. \end{align}\]

Finally, substituting for the constants produces

\[\begin{align} \boxed{(\text{Radius})=r=\dfrac{n^2h^2}{4\pi^2 m \text K Ze^2}}\\ \approx 0.529 \dfrac{n^2}{Z}\si{\angstrom}. \end{align}\]

Deriving the energy of the electron in the \(n^\text{th}\) orbit is quite easy; the total energy of an electron is the sum of its kinetic and potential energies:

\[\begin{align} \textrm{P.E.}&=(\text{Force of Attraction})\times (\text{Radius})\\ &=-\text K\dfrac{Ze^2}{r} \\ \textrm{K.E.}&=\dfrac 12mv^2 \\ &=\dfrac 12m\times \text K\dfrac{Ze^2}{mr}\\ &=\dfrac 12K\dfrac{Ze^2}{r}. \end{align}\]

Thus the total energy is given by the sum of the two results:

\[\begin{align} (\textrm{Total Energy}) &=-\text K\dfrac{Ze^2}{r}+\dfrac 12K\dfrac{Ze^2}{r}\\ &=-\dfrac 12 \text K\dfrac{Ze^2}{r}. \end{align}\]

Replacing the expression for \(r\) returns

\[\text E_n= -\dfrac 12 \text K\dfrac{Ze^2}{n^2h^2} \times 4\pi^2m\text KZe^2,\]

which gives

\[\begin{align} \boxed{(\text{Energy})=E_n=-\dfrac{2\pi^2 m \text K^2Z^2e^4}{n^2h^2}}&\approx -13.6\dfrac{Z^2}{n^2} \text{eV/atom}\\ &\approx -1312\dfrac{Z^2}{n^2} \text{kJ/mol}\\ &\approx -21.6 \times 10^{-19}\dfrac{Z^2}{n^2} \text{J/atom}\\ &\approx -313\dfrac{Z^2}{n^2} \text{kcal/mol}. \end{align}\]

From Bohr's theory \[\begin{align} mvr=\dfrac{nh}{2\pi} \implies v&=\dfrac{nh}{2\pi mr}\\ &=\dfrac{nh}{2\pi m}\times \dfrac{4\pi^2 m\text KZe^2}{n^2h^2}\\ &=\boxed{\dfrac{2\pi \text KZe^2}{nh}=(\text{Velocity})}\\ &\approx 2.188\times 10^6 \dfrac Zn m/s. \end{align}\]

Rotations per second is the velocity of the electron by its circumference, which is given by

\[\begin{align} \textrm{RPS}=\dfrac{(\text{Velocity})}{(\text{Circumference})}&=\dfrac{\hspace{3mm} \dfrac{2\pi \text K Ze^2}{nh}\hspace{3mm} }{2\pi r}\\ &=\dfrac{\text KZe^2}{nh}\times \dfrac{4\pi^2m\text KZe^2}{n^2h^2}\\ &=\boxed{\dfrac{4\pi^2\text K^2mZ^2e^4}{n^3h^3}=\text{RPS}}\\ &\approx 6.58\times 10^{15}\dfrac{Z^2}{n^3}. \end{align}\]

Time period and frequency are related as

\[\text{T.P.}=\dfrac 1{\text{RPS}}.\]

Thus the expression for time period is as follows:

\[\begin{align} \boxed{\text{T.P.}=\dfrac{n^3h^3}{4\pi^2m\text KZ^2e^4}} \approx 1.52\times 10^{-16}\dfrac{n^3}{Z^2}\text{ sec}. \end{align}\]

• AB Lagrelius AND Westphal, . Niels Bohr, physicist. . Retrieved August 24, 2016, from https://commons.m.wikimedia.org/wiki/File:Niels_Bohr.jpg
• JabberWok, . Bohr-atom . Retrieved August 24, 2016, from https://en.wikipedia.org/wiki/Bohr_model#/media/File:Bohr-atom-PAR.svg

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Bohr's Model Of An Atom

What is bohr’s model of an atom.

The Bohr model of the atom was proposed by Neil Bohr in 1915. It came into existence with the modification of Rutherford’s model of an atom. Rutherford’s model introduced the nuclear model of an atom, in which he explained that a nucleus (positively charged) is surrounded by negatively charged electrons.

Introduction to the Bohr Model

Bohr theory modified the atomic structure model by explaining that electrons move in fixed orbitals (shells) and not anywhere in between and he also explained that each orbit (shell) has a fixed energy. Rutherford explained the nucleus of an atom and Bohr modified that model into electrons and their energy levels.

Bohr’s Model of an Atom

Bohr’s model consists of a small nucleus (positively charged) surrounded by negative electrons moving around the nucleus in orbits. Bohr found that an electron located away from the nucleus has more energy, and the electron which is closer to nucleus has less energy

Postulates of Bohr’s Model of an Atom

• In an atom, electrons (negatively charged) revolve around the positively charged nucleus in a definite circular path called orbits or shells.
• Each orbit or shell has a fixed energy and these circular orbits are known as orbital shells.
• The energy levels are represented by an integer (n=1, 2, 3…) known as the quantum number. This range of quantum number starts from nucleus side with n=1 having the lowest energy level. The orbits n=1, 2, 3, 4… are assigned as K, L, M, N…. shells and when an electron attains the lowest energy level, it is said to be in the ground state.
• The electrons in an atom move from a lower energy level to a higher energy level by gaining the required energy and an electron moves from a higher energy level to lower energy level by losing energy.

Recommended Video

Bohr’s model of atom – structure of atom.

Limitations of Bohr’s Model of an Atom

• Bohr’s model of an atom failed to explain the Zeeman Effect (effect of magnetic field on the spectra of atoms).
• It also failed to explain the Stark effect (effect of electric field on the spectra of atoms).
• It violates the Heisenberg Uncertainty Principle .
• It could not explain the spectra obtained from larger atoms.

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Atomic structure – important questions.

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Bohr theory is applicable to

Frequently asked questions – faqs, how do electrons move according to bohr’s model.

The theory notes that electrons in atoms travel around a central nucleus in circular orbits and can only orbit stably at a distinct set of distances from the nucleus in certain fixed circular orbits. Such orbits are related to certain energies and are also referred to as energy shells or energy levels.

How did Bohr discover electrons?

Bohr was the first to discover that electrons move around the nucleus in different orbits and that an element’s properties are determined by the number of electrons in the outer orbit.

Did Bohr’s model have neutrons?

The nucleus in the atom’s Bohr model holds most of the atom’s mass in its protons and neutrons. The negatively charged electrons, which contribute little in terms of mass, but are electrically equivalent to the protons in the nucleus, orbit the positively charged core.

How did Sommerfeld modify Bohr’s theory?

Many modifications have been introduced to the Bohr model, most notably the Sommerfeld model or Bohr – Sommerfeld model, which suggested that electrons move around a nucleus in elliptical orbits rather than circular orbits of the Bohr model. The Bohr – Sommerfeld system was essentially incoherent, contributing to many paradoxes.

Who discovered electrons?

J. J. Thomson in 1897 discovered Electron when he was studying the properties of the cathode ray.

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Bohr atomic model

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Niels Bohr proposed a model of the atom in which the electron was able to occupy only certain orbits around the nucleus. This atomic model was the first to use quantum theory, in that the electrons were limited to specific orbits around the nucleus. Bohr used his model to explain the spectral lines of hydrogen .

What was Niels Bohr’s atomic model?

Niels Bohr modeled the atom with electrons that could only have specific stable orbits. This model of the atom was the first to incorporate quantum theory. That electrons could only occur in specific orbits explained why elements such as hydrogen emitted and absorbed light at specific wavelengths.

Niels Bohr (born October 7, 1885, Copenhagen , Denmark—died November 18, 1962, Copenhagen) was a Danish physicist who is generally regarded as one of the foremost physicists of the 20th century. He was the first to apply the quantum concept, which restricts the energy of a system to certain discrete values, to the problem of atomic and molecular structure. For that work he received the Nobel Prize for Physics in 1922. His manifold roles in the origins and development of quantum physics may be his most-important contribution, but through his long career his involvements were substantially broader, both inside and outside the world of physics .

Bohr was the second of three children born into an upper middle-class Copenhagen family. His mother, Ellen (née Adler), was the daughter of a prominent Jewish banker. His father, Christian, became a professor of physiology at the University of Copenhagen and was nominated twice for the Nobel Prize.

Enrolling at the University of Copenhagen in 1903, Bohr was never in doubt that he would study physics. Research and teaching in that field took place in cramped quarters at the Polytechnic Institute, leased to the University for the purpose. Bohr obtained his doctorate in 1911 with a dissertation on the electron theory of metals.

On August 1, 1912, Bohr married Margrethe Nørlund, and the marriage proved a particularly happy one. Throughout his life, Margrethe was his most-trusted adviser. They had six sons, the fourth of whom, Aage N. Bohr , shared a third of the 1975 Nobel Prize for Physics in recognition of the collective model of the atomic nucleus proposed in the early 1950s.

Bohr’s first contribution to the emerging new idea of quantum physics started in 1912 during what today would be called postdoctoral research in England with Ernest Rutherford at the University of Manchester . Only the year before, Rutherford and his collaborators had established experimentally that the atom consists of a heavy positively charged nucleus with substantially lighter negatively charged electrons circling around it at considerable distance. According to classical physics, such a system would be unstable, and Bohr felt compelled to postulate, in a substantive trilogy of articles published in The Philosophical Magazine in 1913, that electrons could only occupy particular orbits determined by the quantum of action and that electromagnetic radiation from an atom occurred only when an electron jumped to a lower-energy orbit . Although radical and unacceptable to most physicists at the time, the Bohr atomic model was able to account for an ever-increasing number of experimental data, famously starting with the spectral line series emitted by hydrogen .

In the spring of 1916, Bohr was offered a new professorship at the University of Copenhagen; dedicated to theoretical physics, it was the second professorship in physics there. As physics was still pursued in the cramped quarters of the Polytechnic Institute, it is not surprising that already in the spring of 1917 Bohr wrote a long letter to his faculty asking for the establishment of an Institute for Theoretical Physics. In the inauguration speech for his new institute on March 3, 1921, he stressed, first, that experiments and experimenters were indispensable at an institute for theoretical physics in order to test the statements of the theorists. Second, he expressed his ambition to make the new institute a place where the younger generation of physicists could propose fresh ideas. Starting out with a small staff, Bohr’s institute soon accomplished those goals to the highest degree.

Already in his 1913 trilogy, Bohr had sought to apply his theory to the understanding of the periodic table of elements. He improved upon that aspect of his work into the early 1920s, by which time he had developed an elaborate scheme building up the periodic table by adding electrons one after another to the atom according to his atomic model . When Bohr was awarded the Nobel Prize for his work in 1922, the Hungarian physical chemist Georg Hevesy , together with the physicist Dirk Coster from Holland, were working at Bohr’s institute to establish experimentally that the as-yet-undiscovered atomic element 72 would behave as predicted by Bohr’s theory. They succeeded in 1923, thus proving both the strength of Bohr’s theory and the truth in practice of Bohr’s words at the institute’s inauguration about the important role of experiment. The element was named hafnium (Latin for Copenhagen).

What Is Bohr’s Atomic Theory?

Rutherford’s failed model, the hydrogen spectrum, bohr’s atomic model, shortcomings.

Niel Bohr’s Atomic Theory states that – an atom is like a planetary model where electrons were situated in discretely energized orbits. The atom would radiate a photon when an excited electron would jump down from a higher orbit to a lower orbit. The difference between the energies of those orbits would be equal to the energy of the photon.

Niels Bohr was a Danish physicist and is considered one of the founding fathers of quantum mechanics , precisely old quantum mechanics. For his exemplary contributions to science, the Carlsberg brewing company decided to give him a house situated right next to one of their breweries. The house was connected to the brewery by a pipeline. Bohr was rewarded with a lifetime supply of free beer that would pour out of a tap at his whim. What extraordinary feat did Niels Bohr accomplish to deserve this prestigious honor, and well, a Nobel Prize?

Quite simply, Niels Bohr illuminated the mysterious inner-workings of the atom. Although he arrived at his model and its principles in collaboration with the august founder of the atomic nucleus, Ernest Rutherford, the model is only credited to Bohr. Originally called the Rutherford-Bohr atomic model, it is now commonly referred to as Bohr’s atomic model.

To understand Bohr’s theory, we must first understand what prior discoveries led him to pursue his revolutionary ideas.

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It was Sir J.J. Thomson who first discovered that the atom wasn’t indivisible after all, a notion believed to be true for centuries. However, the subatomic particle he discovered was negatively charged. If atoms were merely a cluster of negative charges, then chairs, tables, you and I would be anything but stable. He immediately realized that to account for matter’s stability, there must be a net positive charge to neutralize the negativity.

Thomson devised what became the very first model of an atom. He suggested that the negative particles, which he called electrons, were like seeds embedded in a positively charged watermelon. The model is popularly known as the  plum or raisin pudding model . I’m sure the analogy is obvious.

This view held true until Ernest Rutherford showed that when positive particles are shot at an atom, most of them pass straight through, but a few are observed to be deflected at a large angle. Rutherford realized that most of the atom was filled with empty space, but at the center was a dense, point-like concentration of positive charge. He called this the atom’s nucleus. The volume of empty space between an atom’s electrons and its nucleus is so huge that if the atom were expanded to the size of a baseball stadium, its nucleus would be the size of a baseball.

Rutherford suggested that perhaps the atomic system was analogous to our Solar System, where the electrons revolve around the nucleus like planets revolving around the Sun. The crucial difference was, of course, that the electrons were captivated by electrostatic force, rather than gravity. However, Maxwell and Hertz would have vehemently disagreed.

Maxwell’s laws of electromagnetism had recently established that the motion of a charged particle, such as an electron, comes at the expense of energy. Thus, a revolving electron, like the circus men on motorbikes racing around inside a sphere, would soon spiral and collapse as it ran out of fuel. In fact, physicists calculated that it would take just 16 picoseconds for an electron to radiate all its energy and collapse into its nucleus. That is one-trillionth of a second. A new atomic model that would explain matter’s profound stability had yet to be discovered.

Also Read: What Is J.J. Thomson’s Plum Pudding Model?

Another absurdity that perplexed physicists at that time was Planck’s black body radiation and the “emission spectrum” given off by different atoms. The word ‘spectrum’ was first coined by Newton to describe the rainbow of colors that sprang from his prism.

Similarly, when a body is heated, it radiates a spectrum of electromagnetic energy. If you burn a bar of iron with a blowtorch, you will observe that as the temperature of the bar increases, the color it assumes will also change gradually. First, it’s red, then orange, and then bright white before veering towards violet.

This is because the electromagnetic energy radiated by that iron bar falls in the range of visible light – light that our eyes can detect. If you were to heat the bar to 20,000 Kelvin, the energy radiated would be in the ultraviolet (UV) range. In fact, every object in the Universe radiates such a spectrum of energy, including human beings, but since the temperature of our body is so low, the energy emitted is also meager, somewhere in the range of infrared light. Our eyes are equipped with sensors that can only identify one member amongst the several members of the electromagnetic spectrum.

Max Planck called this phenomenon black body radiation. If you were to plot the heat’s intensity with the wavelength of light radiated, you would observe a peak at a certain range of wavelengths. The peak for the Sun’s core burning at 6,000K lies partly in the visible range, while for a star burning at 20,000K, it lies completely in the UV range, and for a stellar explosion, such as the birth of a black hole , it lies in the gamma range.

Furthermore, the graph depicts that as the temperature of a body declines, the wavelength of light it radiates increases. For instance, the radiation from the Big Bang may have started out as gamma rays, but as it cooled down over more than 13 billion years, the wavelengths elongated to microwaves. If you were to plot these waves on a black background, you would witness a beautiful, hazy mélange of colors – a continuous spectrum.

However, the major implication of Planck’s finding was that the radiated energy traveled in discrete packets, like rigid particles, which Einstein later called photons. The energy of a single quantum is inversely proportional to its wavelength or directly proportional to its frequency. With a fundamental constant of proportionality called Planck’s constant,  h , the energy E for a frequency v   can be expressed as E = hv.

Now, if you were to heat a volume of gas of a single element in this way and plot the colors on a black background, you would observe something of an anomaly. The spectrum is no longer a beautiful or continuous mixture of colors. Instead, it comprises a series of definite, single-colored lines intermittently separated by chunks of the absolutely black background. For instance, take a look at the ever-famous spectrum of hydrogen.

In fact, each and every element in the Universe paints its own unique, discontinuous spectrum. While hydrogen’s spectrum lies in the visible range, certain elements produce a spectrum that lies in the ultraviolet or infrared range. For this reason, an element’s spectrum is considered its fingerprint. The knowledge of its uniqueness allows us to study the composition of stars and has even aided scientists in discovering new elements!

Looking at the spectrum of hydrogen, it was obvious that only certain colors appeared because only certain frequencies – those associated with these colors – were radiated. Given that, why would atoms exhibit this peculiar behavior? What atomic structure would restrict them so severely to express themselves so laconically? Niels Bohr, in 1913, finally realized why.

Bohr went ahead with Rutherford’s Solar System model, but added a small tweak. He rectified its failing aspect by suggesting (for a reason yet to be known) that electrons revolve around a nucleus in fixed or definite orbits. He claimed that in these orbits, the electrons wouldn’t lose any energy, therefore ensuring that they didn’t collapse into the nucleus.

Bohr called these fixed orbits “stationary orbits”. He claimed that the orbits weren’t randomly situated, but were instead at discrete distances from the nucleus in the center, and that each of them was associated with fixed energies. Inspired by Planck’s theory, he denoted the orbits by n, and called it the quantum number .

However absurd the theory might have appeared, it predicted the spectrum of hydrogen splendidly. According to it, when a gas is heated, its energized electrons jump from an orbit of lower energy to an orbit of higher energy (in the case of hydrogen, from n =1 to n = 2). However, to regain stability, they must jump back down to the lower energy orbits. While undergoing this transition, the electron must lose some of its energy, and it is this energy that is radiated in the form of light!

The discrete nature of orbits provides a concise explanation for the discrete nature of photons. Bohr found that the energy of an emitted photon is equal to the difference of energies of the two levels between which the electron makes its jump. For instance, infrared is radiated when the electron makes a short leap, while ultraviolet is radiated when it makes a much larger leap. This relation can be simply expressed as E2 – E1 = hv. Conversely, an electron jumps to a higher orbit when it absorbs a photon.

The spectrum of an atom is restricted to particular colors because its concrete, organized structure allows its electrons to only certain energy transitions – and therefore certain frequencies of light. Now, if an atom of hydrogen only contains a single electron, why does its spectrum consist of multiple colors? Well, this is because the gas is composed of millions and billions of atoms with electrons raised to different orbits that are higher or lower than those nearby.

So, this was Bohr’s model – a planetary model where electrons were situated in discretely energized orbits. The atom would radiate a photon when an excited electron would jump down from a higher orbit to a lower orbit. The difference between the energies of those orbits would be equal to the energy of the photon.

Also Read: Protons And Electrons Have Opposite Charges, So Why Don’t They Pull On Each Other?

Unfortunately, Bohr’s model could only explain the behavior of a system where two charged points orbited each other. This meant the hydrogen atom, in particular. It also included ionized helium (helium has two electrons, so ionization would seize one of those, leaving it with only one) or double-ionized lithium (lithium has three electrons… you do the math). His theory couldn’t explain the behavior of any other atom except hydrogen.

Furthermore, his theory dictated that electrons align in the stationary orbits like beads on a thread, meaning that he had assumed a non-interactive system of electrons. This horribly discounts the violently repulsive electrostatic force between not just two, but multiple electrons clustered together that would thrust each other miles away. Eventually, we discovered that electrons do not just revolve, but also rotate or spin on their axis. Bohr’s model couldn’t explain why this didn’t lead to a loss of energy.

It is speculated that part of the reason why Bohr’s theory was so readily accepted is that it made successful theoretical predictions of multiple spectra that hadn’t been observed. Still, it is widely lauded, as it revolutionized modern physics by paving the way for modern quantum mechanics. Eventually, modern quantum mechanics perfectly explained the true nature of energy shells, how electrons would inhabit each of them, as well as the problem of spin.

However, for its simplicity, Bohr’s ideas still continue to exist and dominate high school physics. The textbooks are replete with concentric circles filled with electrons surrounding a nucleus, which resembles the beads-in-a-thread model. For his contribution, Bohr surely deserved that free beer after all. And of course… a Nobel Prize.

• Bohr Atomic Model.
• Rutherford and Bohr describe atomic structure.
• How are Spectra Produced?.
• Bohr model.

Akash Peshin is an Electronic Engineer from the University of Mumbai, India and a science writer at ScienceABC. Enamored with science ever since discovering a picture book about Saturn at the age of 7, he believes that what fundamentally fuels this passion is his curiosity and appetite for wonder.

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Bohr’s Model of Atom

Quantum mechanics, Quantum physics, the theory of relativity, etc are the modern subjects that interests, astound, and confuse almost everybody. These topics form the basis of modern physics. However, the very first-time quantum theory was incorporated in Bohr’s Model of an atom or Bohr atomic model. Later this model became the predecessor of complete quantum mechanical models .

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The physicist Niels Bohr said, “Anyone who is not shocked by quantum theory has not understood it.”  He also said, “We must be clear that when it comes to atoms, language can only be used as in poetry.”  So what exactly is this  Bohr atomic model? Let us find out!

Bohr atomic model and the models after that explain the properties of atomic electrons on the basis of certain allowed possible values.  The model explained how an atom absorb or emit radiation when electrons on subatomic level jump between the allowed and stationary states. German-born physicists James Franck and Gustav Hertz obtained experimental evidence of the presence of these states.

Introduction to Bohr Atomic Model

A Danish physicist named Neil Bohr in 1913 proposed the Bohr atomic model. He modified the problems and limitations associated with Rutherford’s model of an atom.  Earlier in Rutherford Model, Rutherford explained in an atom a nucleus is positively charged and is surrounded by electrons (negatively charged particles).

Learn about Rutherford’s Atomic Model here in detail .

The electrons move around in a predictable path called orbits . Bohr modified Rutherford’s model where he explained that electrons move around in fixed orbital shells. Furthermore, he explained that each orbital shell has fixed energy levels. Therefore, Rutherford basically explained a nucleus of an atom whereas Bohr took the model one step ahead. He explained about electrons and the different energy levels associated with them.

What is Bohr’s Model of an Atom?

According to the Bohr Atomic model, a small positively charged nucleus is surrounded by revolving negatively charged electrons in fixed orbits. He concluded that electron will have more energy if it is located away from the nucleus whereas electrons will have less energy if it located near the nucleus.

Bohr’s Model of an Atom (Source Credit: Britannica)

Postulates of  Bohr Atomic Model

• Electrons revolve around the nucleus in a fixed circular path termed “orbits” or “shells” or “energy level.”
• The orbits are termed as “stationary orbit.”
• Every circular orbit will have a certain amount of fixed energy and these circular orbits were termed orbital shells. The electrons will not radiate energy as long as they continue to revolve around the nucleus in the fixed orbital shells.
• The different energy levels are denoted by integers such as n=1 or n=2 or n=3 and so on. These are called quantum numbers. The range of quantum numbers may vary and begin from the lowest energy level (nucleus side n=1) to the highest energy level. Learn the concept of an Atomic number here .
• The different energy levels or orbits are represented in two ways such as 1, 2, 3, 4…  or K, L, M, N….. shells.  The lowest energy level of the electron is called the ground state. Learn the concept of Valency here in detail here .
• The change in energy occurs when the electrons jump from one energy level to other. In an atom, the electrons move from lower to higher energy level by acquiring the required energy. However, when an electron loses energy it moves from higher to lower energy level.
• 1 st orbit (energy level) is represented as K shell and it can hold up to 2 electrons.
• 2 nd orbit (energy level) is represented as L shell and it can hold up to 8 electrons.
• 3 rd orbit (energy level) is represented as M shell and it can contain up to 18 electrons.
• 4 th orbit (energy level) is represented as N Shell and it can contain maximum 32 electrons.

The orbits continue to increase in a similar manner.

Watch and Learn more about Modern Atomic Theory

Distribution of Electrons in Orbits or Shells:

Electronic distribution of various orbits or energy levels can be calculated by the formula 2n 2 . Here, ‘n’ denotes the number of orbits.

• The number of electrons in K shell (1st orbit) can be calculated by 2n 2 = 2 x 1 2 = 2. Thus, maximum number of electrons in 1st orbit = 2
• Similarly, The number of electrons in L shell (2nd orbit)= 2 x 2 2 = 8. Thus, maximum number of electrons in 2nd orbit = 8

We can determine the maximum number of electrons in a similar way.

Read about Thomson’s Model of an Atom , the very first model of an Atom by J.J. Thomsons.

You can download Atomic Number Cheat Sheet by clicking on the download button below

Limitations of Bohr’s Model of an Atom

The following are the fundamental limitations of Bohr’s Model of the hydrogen atom.

• Bohr’s model no longer observes the Heisenberg Uncertainty Principle.
• The Neils Bohr atomic version speculation considers electrons to have each recognised function and momentum simultaneously, that’s unthinkable as indicated with the aid of using Heisenberg.
• The Bohr atomic version no longer makes an accurate prediction of large-sized atoms and furnishes enough statistics that are simplest for smaller atoms.
• Bohr’s model does not make clear the Zeeman effect whilst the spectrum is cut up into some wavelengths in the sight of a magnetic field.
• It does not state the Stark effect whilst the spectrum receives separated into nearly negligible strains in the sight of an electric powered field.

What are Isotopes? Learn the concept of Isotopes and Isobars .

Examples on Bohr Atomic Model

Example 1: Calculate the maximum number of electrons an o shell can hold.

Solution: We know that O shell means 5th shell. Therefore, n=5. Applying the formula 2n 2  = 2 x 5 2 = 50 Thus, the maximum number of electrons O shell can hold is 50.

Example 2: What happens when an electron changes its orbit from outer to inner energy? Energy remains constant

Solution: The answer is 4 . Energy is released when an electron jumps from higher to lower energy level.

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Structure of Atom

• Electron Configuration
• Quantum Numbers
• Shapes of Atomic Orbitals
• Energies of Orbitals
• Towards Quantum Mechanical Model of Atom
• Emission and Absorption Spectra
• Development Leading to Bohr’s Model of Atom
• Atomic Models
• Sub-Atomic Particles

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Bohr Model of the Atom

Bohr Model – Core Concepts:

In this tutorial, you will learn what the Bohr Model is, how it improved upon previous models of the atom, and what problems the Bohr model fails to solve.

What is the Bohr Model?

The Bohr Model is a model of an atom. The model was proposed by physicist Niels Bohr in 1913. In this model, the electrons travel around the nucleus of an atom in distinct circular orbits , or shells. The model is also referred to as the planetary model of an atom.

The electrons orbit around the nucleus similar to how planets orbit around the sun. The planets are held in orbit by gravitational force and the electrons are held in their orbit by the electrostatic or Coulomb force between the electrons and protons. In this atomic model, all electrons must exist in a discrete shell and can’t be between shells.

Each shell has a specific energy level, and electrons cannot exist outside of these orbits. The closer the shell is to the nucleus, the smaller the energy of that shell. For an electron to move to another shell it must absorb or release energy. The amount of energy absorbed or emitted is dependent on the difference in energy between the shells.

Energy Release

When the electron moves from a larger higher-energy shell to a smaller lower-energy one it releases energy. The energy is released in the form of light. These discrete energy steps are what cause atomic line spectra, like the one seen for hydrogen below.

Only light of specific energy (or color) is released, shown by the sharp lines seen in the spectra, not all colors of light. For example, the red line would be caused by the electron moving from shell 2 to shell 1. And the blue line would be caused by an electron moving from shell 3 to shell 2. Each orbit change has a unique energy difference.

Atomic line spectra of hydrogen. (From Wikipedia Commons)

Improvements From Previous Models

The Bohr model replaced earlier models such as the plum-pudding model (by J.J. Thomson in 1904), the Saturnian model (by Hantaro Nagaoka in 1904), and the Rutherford model (by Ernest Rutherford in 1911).

Bohr’s model is different from the preceding model (the Rutherford model) because electrons can only orbit at certain radii or energy. It is the first atom model that accounts for quantized or discrete energy steps. No other model had done this before and was a big step towards the development of quantum mechanics.

Using Bohr’s model of the atom the previously observed atomic line spectrum for hydrogen could be explained. Previous models had not been able to explain the spectra.

Hydrogen Bohr Model

The Bohr model of hydrogen is the only one that accurately predicts all the electron energies. When there is more than one electron the model does not accurately predict the energies. Other ions that also have one electron can also be explained accurately (for example, He + ). When there is more than one electron interactions between the nucleus and electrons become too complicated for the Bohr model.  

Problems with Bohr’s Model

• The Bohr atomic model could not accurately describe larger atoms. The emission spectrum of atoms with more than one electron could not be explained.
• The atomic model could not explain the different line intensities in emission spectra.
• The Bohr model did not describe the changes seen in emission spectra when a magnetic field was present (known as the Zeeman effect).
• Does not match what scientists would later learn that an electron can be both a wave and a particle.
• Electrons in circular orbits should emit energy, eventually resulting in their collision with the nucleus.

Bohr Atomic Model Fun Facts

• Niels Bohr was awarded the Nobel Prize in physics in 1922 for his work investigating the structure of an atom
• In his later years, Niels Bohr advocated for openness between nations in atomic weapons development.
• Niels Bohr helped rescue and provide jobs for scientists escaping Germany during the Nazi regime by giving them positions at the theoretical physics institute he ran and helping them get visas to other countries.
• The Bohr model is the one most often depicted when drawing an atom.

Further Reading

• Rutherford Atomic Model
• Atomic Spectra

Niels Bohr: Biography & Atomic Theory

Niels Bohr was one of the foremost scientists of modern physics, best known for his substantial contributions to quantum theory and his Nobel Prize -winning research on the structure of atoms.

Born in Copenhagen in 1885 to well-educated parents, Bohr became interested in physics at a young age. He studied the subject throughout his undergraduate and graduate years and earned a doctorate in physics in 1911 from Copenhagen University.

While still a student, Bohr won a contest put on by the Academy of Sciences in Copenhagen for his investigation into the measurements of liquid surface tension using oscillating fluid jets. Working in the laboratory of his father (a renowned physiologist), Bohr conducted several experiments and even made his own glass test tubes. 

Bohr went above and beyond the current theory of liquid surface tension by taking into account the viscosity of the water as well as incorporating finite amplitudes rather than infinitesimal ones. He submitted his essay at the last minute, winning first place and a gold medal. He improved upon these ideas and sent them to the Royal Society in London, who published them in the journal Philosophical Transactions of the Royal Society in 1908, according to Nobelprize.org . 

His subsequent work became increasingly theoretical. It was while conducting research for his doctoral thesis on the electron theory of metals that Bohr first came across Max Planck's early quantum theory, which described energy as tiny particles, or quanta.

In 1912, Bohr was working for the Nobel laureate J.J. Thompson in England when he was introduced to Ernest Rutherford, whose discovery of the nucleus and development of an atomic model had earned him a Nobel Prize in chemistry in 1908. Under Rutherford's tutelage, Bohr began studying the properties of atoms.

Bohr held a lectureship in physics at Copenhagen University from 1913 to 1914 and went on to hold a similar position at Victoria University in Manchester from 1914 to 1916. He went back to Copenhagen University in 1916 to become a professor of theoretical physics. In 1920, he was appointed the head of the Institute for Theoretical Physics.

Combining Rutherford's description of the nucleus and Planck's theory about quanta, Bohr explained what happens inside an atom and developed a picture of atomic structure. This work earned him a Nobel Prize of his own in 1922.

In the same year that he began his studies with Rutherford, Bohr married the love of his life, Margaret Nørlund, with whom he had six sons. Later in life, he became president of the Royal Danish Academy of Sciences, as well as a member of scientific academies all over the world.

When the Nazis invaded Denmark in World War II, Bohr managed to escape to Sweden. He spent the last two years of the war in England and the United States, where he got involved with the Atomic Energy Project. It was important to him, however, to use his skills for good and not violence. He dedicated his work toward the peaceful use of atomic physics and toward solving political problems arising from the development of atomic weapons of destruction. He believed that nations should be completely open with one another and wrote down these views in his Open Letter to the United Nations in 1950.

Atomic model

Bohr's greatest contribution to modern physics was the atomic model. The Bohr model shows the atom as a small, positively charged nucleus surrounded by orbiting electrons. 

Bohr was the first to discover that electrons travel in separate orbits around the nucleus and that the number of electrons in the outer orbit determines the properties of an element.

The chemical element bohrium (Bh), No. 107 on the periodic table of elements , is named for him.

Liquid droplet theory

Bohr's theoretical work contributed significantly to scientists' understanding of nuclear fission . According to his liquid droplet theory, a liquid drop provides an accurate representation of an atom's nucleus.

This theory was instrumental in the first attempts to split uranium atoms in the 1930s, an important step in the development of the atomic bomb.

Despite his contributions to the U.S. Atomic Energy Project during World War II, Bohr was an outspoken advocate for the peaceful application of atomic physics.

Quantum theory

Bohr's concept of complementarity, which he wrote about in a number of essays between 1933 and 1962, states that an electron can be viewed in two ways, either as a particle or as a wave, but never both at the same time.

This concept, which forms the basis of early quantum theory, also explains that regardless of how one views an electron, all understanding of its properties must be rooted in empirical measurement. Bohr's theory stresses the point that an experiment's results are deeply affected by the measurement tools used to carry them out.

Bohr's contributions to the study of quantum mechanics are forever memorialized at the Institute for Theoretical Physics at Copenhagen University, which he helped found in 1920 and headed until his death in 1962. It has since been renamed the Niels Bohr Institute in his honor.

Niels Bohr quotations

"Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it."

"Everything we call real is made of things that cannot be regarded as real."

"The best weapon of a dictatorship is secrecy, but the best weapon of a democracy should be the weapon of openness."

"Never express yourself more clearly than you are able to think."

Additional reporting by Traci Pedersen, Live Science contributor

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Elizabeth is a former Live Science associate editor and current director of audience development at the Chamber of Commerce. She graduated with a bachelor of arts degree from George Washington University. Elizabeth has traveled throughout the Americas, studying political systems and indigenous cultures and teaching English to students of all ages.

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Niels Bohr Atomic Model Theory Experiment

Niels Bohr Education & Life

Niels Bohr is a well-known Danish physicist that spent the majority of his life studying the atomic model. The atomic model is a theory that holds that the atoms in an element are different from one another and contain protons, electrons, and neutrons.

What Was Niels Bohr Experiment? What Did Niels Bohr Discover?

The Niels Bohr Atomic Model theory is a model that was introduced by Niels Bohr in 1913 to describe the atom. It was a postulation of Bohr that the electrons rotated in a circular orbit around the nucleus of the atom.

Niels Bohr’s atomic model was created based on previous research by Rutherford, Rutherford’s gold foil experiment, and Ernest Rutherford’s model of the atom.

In his model, Bohr postulated that electrons were placed in orbits that are referred to as orbitals. Atoms consist of a central nucleus, surrounded by electrons in orbital shells.

The electrons sit in energy levels around the nucleus, with the lowest possible energy level being electron number one and the highest being electron number eight.

The Bohr atomic model theory states that atoms are composed of a nucleus, which consists of one or more protons and neutrons that are held together by nuclear forces.

It is also known as a hydrogen atom model or the Rutherford-Bohr Atomic Model Theory.

Niels Bohr was a Danish physicist who had a theory about atoms that he called the “atomic model”. Bohr’s atomic model had a nucleus with a certain number of positively charged particles that were held together by negatively charged particles. The electrons would orbit around the nucleus of the atom.

Atomic Model Theory is the idea that the electrons orbiting the atom don’t orbit around a stationary nucleus like they were on the earth in a solar system. Instead, the electrons orbit around the nucleus of the atom, which is constantly moving.

This is what Bohr called his quantum leap. Bohr’s theory helped to explain the interference experiment and helped to create quantum theories, like the wave-particle duality

Niels Bohr came up with a model of the atom that was entirely radical for its time. It contradicted much of what was previously believed about atoms and electrons.

He believed that an electron orbits a nucleus, which is made up of a group of subatomic particles. Bohr received the Nobel Prize in 1922 for his theory.

Niels Bohr As A Physicist

Niels Bohr is considered to be one of the greatest physicists in history. He worked for many years on physics, teaching, and management. This work led him to become a professor at the University of Copenhagen for thirty years.

In 1912, he was offered a professorship at the Institute of Theoretical Physics in Stockholm. However, there was a problem with his salary because he was not on an equal footing with his counterpart at Uppsala University.

In 1920, Bohr returned to the Institute of Theoretical Physics in Copenhagen. To this day, Bohr remains one of the most celebrated people in Danish history.

Niels Bohr as a Father and a Husband

In 1908, Niels Bohr married Margrethe Nørlund. They had two sons, Aage Nørlund (1909) and Harald Bohr (1911). In 1920, they moved to King’s Gate No.1.

They remained there for the rest of their lives. Bohr was a caring husband and father, who did not like to leave home too often because he missed his family.

Bohr also liked to play classical music, and he was a good enough pianist to give concerts in Copenhagen.

Niels Bohr’s Death

In 1942, Niels Bohr became increasingly ill and was diagnosed with an incurable muscle disease, which caused him great pain and robbed him of his ability to walk.

In September 1948, Bohr became very ill. He developed a blood clot in his leg and he could no longer move around on his own. On October 17, he suffered a severe stroke. He passed away on 18 November.

After his death, the Danish king said about Bohr: “I know of no one who has contributed more to the knowledge and to the progress of mankind than Niels Bohr”.

Niels Bohr’s Legacy

One of the most important things that Niels Bohr did was to create a new model of the atom. He realized that electrons could exist in ‘allowed’ orbits, but they could also ‘jump’, or transition, to higher energy orbits.

One way that people continued to think about Bohr’s ideas was through the use of his concept of quantum jumps.

Bohr also believed that the electron didn’t exist in any particular orbit, but instead was found in all orbits all at the same time, and that only when we looked at an atom would it ‘decide’ which orbit to be in.

He was awarded the Nobel Prize for physics in 1922 for this work.

The Bohr Model of The Atom

Bohr’s model of the atom was one of the most important contributions of his career because it helped us to understand why atoms didn’t collapse.

However, Bohr’s model didn’t explain all the properties of an atom. For example, in the ‘old model of the atom, electrons were stationary (always in the same orbit), and they were at a fixed distance from their nucleus. In other words, they orbited at a fixed distance from their nucleus.

Now, with Bohr’s model, this wasn’t true anymore – electrons could jump around to different orbits. It’s easy to understand that if electrons can jump around, then they can’t have a fixed distance from the nucleus. They would also have to be influenced by the nucleus.

So, when you measure any of the properties of an atom (e.g. the position of an electron), you can never measure it as if it were in ‘absolute space’, but only as how things are relative to each other (relative motion).

What Is Niels Bohr Known For?

The physics community remembers Niels Bohr for his work with the Bohr model of the atom. He was able to explain and interpret vast amounts of experimental data in terms of his atomic model.

The Bohr atomic model consists of one positively charged nucleus surrounded by electrons, which are negatively charged.

The positive charge in the nucleus is balanced by negative charge in the electron. Bohr argued that electrons move around the atom by radially oscillating, which wiggles their position in space.

Bohr also thought that atoms could be described as a series of stationary orbitals. An orbital can be considered a “shell” around an electron and “is filled” with electrons.

Energy can be transferred between an orbital and the electron by oscillations. Bohr provided the mathematical description of his model by applying quantum mechanics.

For example, the electron orbits are given by Schrödinger wave equations. The radius of the orbits is related to energy levels in a very simple way.

These are the most basic atomic model equations ever published. All other models have been derived from these basic ones.

Bohr himself made sure that the model could be applied to spectroscopy and other measurements.

What Is Niels Bohr Famous For?

Niels Bohr was a physicist who made fundamental contributions to the theory of the atom, quantum mechanics, and chemical bonding.

He is also known as the father of modern quantum physics. Bohr was one of the first to apply mathematics to physics. He was able to think in terms of waves and positions instead of just particles and points.

Niels Bohr’s Influence On Chemistry

Bohr’s influence also extended beyond physics. In fact, he made some interesting contributions to chemistry.

For example, he correctly predicted that helium atoms would absorb high-frequency light in a series of elements (helium, neon, argon, and krypton).

He also predicted that they would emit light in a series of elements (for example sodium). But perhaps his most important contribution to chemistry was helping to explain why certain chemical reactions occur.

Bohr’s ideas about quantum jumps also helped us to understand how hydrogen, which has a very large atomic mass, could be broken up into its component atoms.

He explained that a hydrogen atom consists of only one electron which moves around the nucleus. The electron orbits the nucleus and then jumps to a new energy level.

Another of Bohr’s greatest contributions was his work in spectroscopy. He correctly predicted that the frequency of light would increase when light passed through a series of metals (such as helium and sodium).

He also predicted that these elements would emit photons at visible frequencies when heated.

The Bohr Model And Quantum Mechanics

While the basic idea behind Bohr’s model (the atom is made up of electrons that move around a nucleus) is still in use today, it was eventually superseded by quantum mechanics .

However, Bohr’s ideas were very important for understanding how atoms worked. He showed how the strangeness of quantum physics explained why atoms didn’t collapse.

He also showed how the strangeness of quantum physics could be used to explain how atoms absorb and emit light.

While Bohr’s model did not explain some of the properties of atoms (mass, charge, or size), it had a major influence on the way that we think about and study atoms today.

Niels Bohr And Experimental Data

Bohr was a physicist who was very important to experimentalists. His contributions helped to explain how electrons could jump from one orbit to another in an atom.

It also helped explain why different atoms have different masses and predicted light emission colors for various kinds of spectroscopy.

In addition, Bohr was one of the first to suggest that the cathode rays (later to be called electrons) do not actually have a definite trajectory but instead travel in a broad wave with peaks and troughs. The wave theory described the behavior of electrons much better than the Newtonian particle model, which had been used up until then.

What Did Niels Bohr Think About The Atom And Quantum Mechanics?

According to Bohr, an atom is composed of a charged nucleus and a cloud of electrons. The nucleus is fixed in space, while the electrons can move around inside the atom.

This movement happens very quickly but is maintained by electromagnetic forces. It is also maintained by the energy which keeps the electrons in their orbits. Ionization occurs when an electron jumps from one orbit to another – or when light from a specific wavelength enters an atom.

Bohr was very conscious of the fact that he was a ‘complementary’ physicist. This means that he accepted quantum theory, but also believed in the classical view (which has all particles having definite locations).

In his day, this challenged the idea of quantum mechanics, since it meant that Bohr himself did not believe in quantum theory.

This is because Bohr did not equate the accuracy of his predictions with the validity of theoretical physics.

However, since he never really discussed these views with his colleagues, and because the laws of quantum mechanics were absolutely consistent with all of his predictions, Bohr did not suffer any significant criticism.

What Was Niels Bohr’s Contribution To Quantum Mechanics?

In 1913 Bohr began working on what we now call the “old” model of an atom. Before this time, it was thought that electrons orbited the nucleus in evenly spaced orbits.

It was also thought that electrons jumped to a new orbit when they gained or lost energy. Bohr changed this view completely by introducing the idea of stationary, allowed orbits.

This meant that electrons had a certain angular momentum inside the atom, which was ever-changing.

An electron could jump to another orbit by losing or gaining energy but did not jump because of an external push or pull. In other words, electrons jump because they are excited by the electromagnetic radiation of an atom.

The idea of stationary allowed orbits was revolutionary. It meant that atoms could emit and absorb energy in a continuous way, rather than in individual packets (which is what happened when people used the Bohr-Ellsberg-Slater theory).

In 1914, Bohr suggested that electrons could exist only in certain orbits inside the atom. This meant that there was a mathematical connection between atomic orbitals and wavelengths or frequencies of light.

Later, in 1916, Bohr suggested that the atom is mainly made of neutrons. He also introduced the idea of electron jumping. This was significant because it was one of the first models to combine quantum theory and classical physics.

In 1918 Bohr published an explanation for atomic structure based on a “postulate” about what happened when electrons jumped from one orbit to another.

According to Bohr, electrons could exist only in certain orbits (i.e., certain energy levels). Electrons could also jump from one orbit into another.

This was an important development in quantum mechanics because it helped to explain why the atom would not collapse.

What Did Niels Bohr Contribute To Society?

Bohr was one of the founders of quantum mechanics. This theory is still in use today. In addition, Bohr was one of the first people to think about atoms – what they might be like and how we can observe them.

He developed models which are still used today.

Besides this, Bohr was a very successful teacher and mentor. Many young scientists (including future Nobel Prize winners) studied with him in Copenhagen and benefited from his advice and guidance.

Niels Bohr was one of the first people to suggest that the laws of classical physics could be thought of as being the same as the laws of quantum physics.

This was a revolutionary idea, and it showed that everything in our world is quantifiable. In other words, nothing in our world can escape quantification – or measurement.

This view of reality – or what we would call ‘the scientific method’ – has had a huge influence on modern thinking about how our society works.

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