what experiment did niels bohr use

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The Bohr Model: Quickly Replaced But Never Forgotten

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Key Takeaways

• Niels Bohr's model, which depicted electrons orbiting the nucleus like planets around the sun, was awarded a Nobel Prize in 1922 despite being technically incorrect.
• Arnold Sommerfeld enhanced the Bohr model in 1916 with elliptical orbits.
• In spite of its inaccuracies, the Bohr model remains a fundamental teaching tool in introducing the concept of atoms.

You can search for a picture of an atom on the internet and you'll find one, even though nobody's actually seen an atom before. But we've got an estimation of what a single atom looks like because of the work of a bunch of different scientists like Danish physicist Niels Bohr.

Atoms are the building blocks of matter — a single atom of any individual element is the most basic entity in nature that still abides by the rules of physics we can observe in everyday life (the subatomic particles that make up atoms have their own special rules). Scientists suspected atoms existed for a long time before they could conceptualize their structure — even the ancient Greeks figured the matter of the universe was made up of components so small they couldn't be broken down into anything smaller, and they called these fundamental units atomos , which means "undivided." By the end of the 19th century, it was understood that chemical substances could be broken down into atoms, which were very small and atoms of different elements had a predictable weight.

But then, in 1897, British physicist J.J. Thomson discovered electrons — negatively-charged particles inside the atoms everyone had spent the better part of a century believing were entirely indivisible — as the smallest things that existed. Thomson just hypothesized that electrons existed, but he couldn't work out exactly how electrons fit into an atom. His best guess was the " plum pudding model ," which depicted the atom as a positively-charged pie studded with negatively-charged areas scattered throughout like fruit in an old-timey dessert.

"Electrons were found to be negative electric, and all with the same mass and very small compared with atoms," says Dudley Herschbach, a Harvard chemist who shared the Nobel Prize in Chemistry in 1986 for his "contributions concerning the dynamics of chemical elementary processes," in an email. "Ernest Rutherford discovered the nucleus in 1911. Nuclei were positive electric, with various masses but much larger than electrons, yet very small in size."

A Giant Leap Forward

Niels Bohr was Rutherford's student who gamely took over his mentor's project of deciphering the structure of the atom in 1912. It took him only a year to come up with a working model of a hydrogen atom.

"Bohr's model of 1913 for the hydrogen atom had circular electron orbits about the proton — like Earth orbits around the sun," says Herschbach. "Bohr had made use of a simple and regular pattern for the spectrum of the hydrogen atom, which had been found by Johann Balmer in 1885. He also made use of the idea of the quantum idea, found by Max Planck in 1900."

In 1913, the Bohr's model was a giant leap forward because it incorporated features of the newborn quantum mechanics into the description of atoms and molecules. That year, he published three papers on the constitution of atoms and molecules: The first and most famous was devoted to the hydrogen atom and the other two described some elements with more electrons, using his model as a framework. The model he proposed for the hydrogen atom had electrons moving around the nucleus, but only on special tracks with different energy levels. Bohr hypothesized that light was emitted when an electron jumped from a higher energy track to a lower energy track — that's what made hydrogen glow in a glass tube. He got hydrogen right, but his model was a little glitchy.

"The model failed to predict the right value of the ground-state energies of many-electron atoms and binding energies of the molecules — even for the simplest 2-electron systems, such as the helium atom or a hydrogen molecule," says Anatoly Svidzinsky, a professor in the Institute for Quantum Science and Engineering at Texas A&M, in an email interview. "So, already in 1913, it was clear that Bohr's model is not quite correct. Even for the hydrogen atom, the Bohr's model incorrectly predicts that atom's ground state possesses nonzero orbital angular momentum."

The 1922 Nobel Prize

Which, of course, might not make a lot of sense to you if you're not a quantum physicist. However, Bohr's model was fast-tracked to receive a Nobel Prize in physics in 1922. But even as Bohr was cementing his reputation in the world of physics, scientists were improving upon his model:

"Bohr's model for the hydrogen atom was improved by Arnold Sommerfeld in 1916," says Herschbach. "He found elliptical orbits which accounted for spectra lines nearby those that had come from circular orbits. The Bohr-Sommerfeld model for the hydrogen atom is basic, but quantum and relativity became major aspects."

Between 1925 and 1928, Werner Heisenberg, Max Born, Wolfgang Pauli, Erwin Schrodinger and Paul Dirac developed these aspects far beyond Bohr's atomic model, but his is by far the most recognized model of an atom. The atomic models quantum physics have given us look less like a sun surrounded by electron planets and more like modern art. It's likely we still use the Bohr model because it's a good introduction to the concept of an atom.

"In 1913, Bohr's model demonstrated that quantization is a right way to go in the description of the micro-world," says Svidzinsky. "Thus, Bohr's model showed scientists a direction to search and stimulated further development of quantum mechanics. If you know the path, then sooner or later you will find the right solution to the problem. One can think of the Bohr's model as one of the direction signs along a hiking trail into the quantum world."

Niels Bohr's father, Christian Bohr , was nominated for three different Nobel Prizes in the Physiology of Medicine, though he never won.

Frequently Asked Questions

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13.7 Cosmos & Culture

The idea that changed the world: 100 years of quantum jumps.

Marcelo Gleiser

One hundred years ago Niels Bohr introduced the idea of quantum jumps with his model of the atom. Since then, and in unexpected ways, quantum physics has taken over the world.

Niels Bohr in September 1953 Keystone/Getty Images hide caption

Niels Bohr in September 1953

Seeing the world through a quantum lens brought us some of the most transformative technological innovations of the 20 th century: nuclear energy (and bombs), transistors and semiconductors, lasers and all the digital technology used in cell phones and computers, GPS navigation, medical-imaging equipment and so much more. And it's the gift that keeps on giving, with quantum computers and myriad nanotechnology applications looming on the horizon.

All of this innovation started with a small group of people trying to figure out the physics of atoms and of subatomic particles, never dreaming that their discoveries would transform the way we live and how we look at nature.

It's telling that Bohr's model of the atom is kind of crazy. It was a collage of ideas, the fruit of his own amazing intuition as he mixed old and new concepts.

Looking only at the simplest of all atoms, that of hydrogen, Bohr imagined it as a mini solar system, with a proton circled by an electron. Following the physicist's way of doing things, he wanted to explain some of the observed data with the simplest possible model. (This is what we refer to as Ockham's Razor — always try to find the simplest explanation for, if it works, it will tend to be the right one.)

Bohr knew that the atom was not a simple solar system: planets have been going around the sun for billions of years, practically without losing any energy. The electron, instead, would spiral into the nucleus almost immediately, at least according to classical electromagnetism. (The electron, being negatively charged, is attracted to the proton, which is positive. As it circled the proton it would radiate away its energy and fall in.)

To salvage the atom, Bohr had to invent new rules that clashed with classical physics. He bravely put forward his idea, suggesting the implausible: what if the electron could only move in certain orbits, separated in space like the steps of a ladder. The same way that you can't stand between steps, the electron couldn't stay in the space between two orbits. It can only jump from one to another, as we can jump between steps. These are the famous quantum jumps.

And how are these quantum orbits determined? Again, we bow to Bohr's amazing intuition. But first, let's make a foray into angular momentum . (If bored by thinking about physics, skip the next two paragraphs. But I hope you don't!) If electrons circle protons, they have what we call angular momentum , a quantity that measures the intensity (and orientation) of circular motions.

If you tie a rock to a string and spin it, it will have angular momentum. The faster you spin, or the longer the string, or the heavier the rock, the larger its angular momentum. If nothing changes (i.e., spin and length of the rock), angular momentum is conserved. (It never is in everyday life due to friction.) When a whirling ice skater spins up by bringing her stretched arms to her chest she is using her (nearly conserved) angular momentum: shorter arms and more spin gives the same angular momentum as longer arms and slower spin.

Bohr suggested that the electron's angular momentum should be quantized, that is, it could only have certain values, set by the integers (n = 1, 2, 3, ... ). If L is the electron's orbital angular momentum, Bohr's formula reads, L = n (h/2π), where h is the famous Planck constant .

The constant is, of course, named after Max Planck , the physicist who in 1900 realized that every energy exchange between atoms and light occurs in chunks. So, Planck planted the seed of the quantum jump idea in physics.

But back to Bohr, a quantized angular momentum meant that the electron's orbits were quantized, or separated in space. The electron could go from one to the other by jumping either down and closer to the proton, or moving up and farther away.

Bohr's brilliant insight was to mix concepts from classical physics with the brand new quantum physics, creating a hybrid model of the atom.

In the process, Bohr also solved an age-old mystery in physics: what determines the colors ( emission spectrum ) a chemical element emits when it's heated up?

The strong yellow in sodium lamps is a familiar example of the dominant color in an emission spectrum. It turns out that each chemical element has its very own spectrum, characterized by a distinctive set of colors. They are an element's spectral fingerprints. Spectra were known throughout the 19 th century, but no one knew why they existed.

Bohr suggested that when an electron jumps between orbits, it either emits or absorbs a chunk of light. These chunks of light are called photons , Albert Einstein's key contribution to quantum physics. (There were many others, but this was the one that gave him his Nobel and that he considered his most revolutionary, even more than relativity. It's the notion that light can be thought of as being either a wave or particles.)

The emission spectrum of an element consisted of the photons (or radiation) electrons gave off when they jumped from higher orbits to lower ones. The photons carried away the angular momentum the electron lost as it jumped down. Bohr suggested that the energy of the photons matched the energy difference between the two orbits.

And why do different elements have different emission spectra? Since each atom has a certain number of protons in its nucleus, its electrons are attracted with different intensity; each allowed orbit will have its specific energy. When the electron jumps, the photon emitted will have that precise energy and no other. Back to the ladder analogy, it is as if each chemical element has its own ladder with steps at different distances from one another. With this, Bohr explained the emission spectrum of hydrogen, a triumph of his hybrid model.

Even if incomplete, Bohr's theory captured the essence of the bizarre quantum behavior of atoms: their quantized orbits and the dance between matter and light. That quantum physics still surprises and puzzles us shows that a century after Bohr's atom we are only beginning to unveil what really goes on in the world of the very small.

You can keep up with more of what Marcelo is thinking on Facebook and Twitter: @mgleiser

• quantum mechanics

The Bohr model: The famous but flawed depiction of an atom

The Bohr model is neat, but imperfect, depiction of atom structure.

• Discovering the structure of atoms

Niels Bohr and quantum theory

• Bohr model and the hydrogen atom
• Bohr model shortcomings

Additional resources:

Bibliography.

The Bohr model, introduced by Danish physicist Niels Bohr in 1913, was a key step on the journey to understand atoms .

Ancient Greek thinkers already believed that matter was composed of tiny basic particles that couldn't be divided further. It took more than 2,000 years for science to advance enough to prove this theory right. The journey to understanding atoms and their inner workings was long and complicated. 

It was British chemist John Dalton who in the early 19th century revived the ideas of ancient Greeks that matter was composed of tiny indivisible particles called atoms. Dalton believed that every chemical element consisted of atoms of distinct properties that could be combined into various compounds, according to Britannica .  

Dalton's theories were correct in many aspects, apart from that basic premise that atoms were the smallest component of matter that couldn't be broken down into anything smaller. About a hundred years after Dalton, physicists started discovering that the atom was, in fact, really quite complex inside. 

Related: There's a giant mystery hiding inside every atom in the universe

The Bohr model: Journey to find structure of atoms

British physicist Joseph John Thomson made the first major breakthrough in the understanding of atoms in 1897 when he discovered that atoms contained tiny negatively charged particles that he called electrons . Thomson thought that electrons floated in a positively charged "soup" inside the atomic sphere, according to Khan Academy .

14 years later, New Zealand-born Ernest Rutherford, Thomson's former student, challenged this depiction of the atom when he found in experiments that the atom must have a small positively charged nucleus sitting at its center. 

Based on this finding, Rutherford then developed a new atom model, the Rutherford model. According to this model, the atom no longer consisted of just electrons floating in a soup but had a tiny central nucleus, which contained most of the atom's mass. Around this nucleus, the electrons revolved similarly to planets orbiting the sun in our solar system , according to Britannica .

Some questions, however, remained unanswered. For example, how was it possible that the electrons didn't collapse onto the nucleus, since their opposite charge would mean they should be attracted to it? Several physicists tried to answer this question including Rutherford's student Niels Bohr.

Bohr was the first physicist to look to the then-emerging   quantum theory to try to explain the behavior of the particles inside the simplest of all atoms; the atom of hydrogen. Hydrogen atoms consist of a heavy nucleus with one positively-charged proton around which a single, much smaller and lighter, negatively charged electron orbits. The whole system looks a little bit like the sun with only one planet orbiting it. 

Bohr tried to explain the connection between the distance of the electron from the nucleus, the electron's energy and the light absorbed by the hydrogen atom, using one great novelty of physics of that era: the Planck constant. 

The Planck constant was a result of the investigation of German physicist Max Planck into the properties of electromagnetic radiation of a hypothetical perfect object called the black body. 

Strangely, Planck discovered that this radiation, including light, is emitted not in a continuum but rather in discrete packets of energy that can only be multiples of a certain fixed value, according to Physics World .That fixed value became the Planck constant. Max Planck called these packets of energy quanta, providing a name to the completely new type of physics that was set to turn the scientists' understanding of our world upside down.

The Bohr model and the hydrogen atom

What role does the Planck constant play in the hydrogen atom? Despite the nice comparison, the hydrogen atom is not exactly like the solar system. The electron doesn't orbit its sun —the nucleus — at a fixed distance, but can skip between different orbits based on how much energy it carries, Bohr postulated. It may orbit at the distance of Mercury , then jump to Earth , then to Mars . 

The electron doesn't slide between the orbits gradually, but makes discrete jumps when it reaches the correct energy level, quite in line with Planck's theory, physicist Ali Hayek explains on his YouTube channel .

Bohr believed that there was a fixed number of orbits that the electron could travel in. When the electron absorbs energy, it jumps to a higher orbital shell. When it loses energy by radiating it out, it drops to a lower orbit. If the electron reaches the highest orbital shell and continues absorbing energy, it will fly out of the atom altogether.

The ratio between the energy of the electron and the frequency of the radiation it emits is equal to the Planck constant. The energy of the light emitted or absorbed is exactly equal to the difference between the energies of the orbits and is inversely proportional to the wavelength of the light absorbed by the electron, according to Ali Hayek.

Using his model, Bohr was able to calculate the spectral lines — the lines in the continuous spectrum of light — that the hydrogen atoms would absorb. 

The shortcomings of the Bohr model

The Bohr model seemed to work pretty well for atoms with only one electron. But apart from hydrogen, all other atoms in the periodic table have more, some many more, electrons orbiting their nuclei. For example, the oxygen atom has eight electrons, the atom of iron has 26 electrons.

Once Bohr tried to use his model to predict the spectral lines of more complex atoms, the results became progressively skewed.

There are two reasons why Bohr's model doesn't work for atoms with more than one electron, according to the Chemistry Channel . First, the interaction of multiple atoms makes their energy structure more difficult to predict. 

Bohr's model also didn't take into account some of the key quantum physics principles, most importantly the odd and mind-boggling fact that particles are also waves, according to the educational website Khan Academy .

As a result of quantum mechanics, the motion of the electrons around the nucleus cannot be exactly predicted. It is impossible to pinpoint the velocity and position of an electron at any point in time. The shells in which these electrons orbit are therefore not simple lines but rather diffuse, less defined clouds. 

 — Massive Space Structures Have Surprising Connection to Quantum Mechanics Math —   Why Can't Quantum Mechanics Explain Gravity? (Op-Ed) — Do We Live in a Quantum World?  

Only a few years after the model's publication, physicists started improving Bohr's work based on the newly discovered principles of particle behavior. Eventually, the much more complicated quantum mechanical model emerged, superseding the Bohr model. But because things get far  less neat when all the quantum principles are in place, the Bohr model is probably still the first thing most physics students discover in their quest to understand what governs matter in the microworld. 

Read more about the Bohr atom model on the website of the National Science Teaching Association or watch this video .

Heilbron, J.L., Rutherford–Bohr atom, American Journal of Physics 49, 1981 https://aapt.scitation.org/doi/abs/10.1119/1.12521

Olszewski, Stanisław, The Bohr Model of the Hydrogen Atom Revisited, Reviews in Theoretical Science, Volume 4, Number 4, December 2016 https://www.ingentaconnect.com/contentone/asp/rits/2016/00000004/00000004/art00003

Kraghm Helge, Niels Bohr between physics and chemistry, Physics Today, 2013 http://materias.df.uba.ar/f4Aa2013c2/files/2012/08/bohr2.pdf

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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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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

Sign up for the Live Science daily newsletter now

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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: Biography and contributions to atomic energy

Biography of niels bohr, birth and early years, bohr's atomic model, copenhagen institute of theoretical physics, contribution to atomic energy, nobel prize in physics, niels bohr's contributions to atomic models, niels bohr's contributions to nuclear energy, nuclear fision, development of nuclear reactors, legacy and conclusion.

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• Niels Bohr - Nobel Lecture: The Structure of the Atom

Nobel Lecture

Nobel Lecture, December 11, 1922

The Structure of the Atom

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How does Niels Bohr's atomic model work?

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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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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Introduction

Niels Henrik David Bohr was born on October 7, 1885, in Copenhagen, Denmark. His father was a professor at the University of Copenhagen. Niels was a good student. He was even better at sports. He and his brother were excellent soccer players. In high school, Niels showed a talent for mathematics and physics. In 1903 he went to the University of Copenhagen to study physics. He earned a Ph.D. in 1911.

Bohr Atomic Model

Bohr made his own model of the atom. He claimed that electrons could only occupy particular orbits around the nucleus. He also explained that when an electron jumped from an outer orbit to an inner orbit, energy would be given off. An electron would absorb energy if it jumped from an inner orbit to an outer orbit.

In 1916 Bohr returned to the University of Copenhagen to work as a professor. There he became director of the Institute for Theoretical Physics in 1920. He won the Nobel Prize in physics in 1922.

A Refuge for Jewish Scientists

When Adolf Hitler and the Nazi Party took power in Germany in 1933, many Jewish scientists were no longer allowed to work in their German homeland. Bohr used his connections in Denmark to help scientists get out of Germany and to work at his institute at Copenhagen University. From there, scientists would obtain permanent appointment elsewhere, most often in the United States.

The Atomic Bomb

Bohr himself was of Jewish descent. Eventually the Nazis occupied his country. He was warned that the Nazis were planning to arrest him. He escaped Copenhagen in 1943. After that, he moved to England and then the United States. At that time, World War II was going on. Scientists in Europe and the United States were afraid that Germany was trying to develop an atomic bomb. Bohr helped scientists in the United States develop their own atomic bomb.

After the war, Bohr returned to Denmark. He continued to direct the institute at Copenhagen University. His son Aage worked there as well. Bohr died in Copenhagen on November 18, 1962. Aage became director of the institute after that and later won a Nobel Prize as well.

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