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
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.
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 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.
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., RutherfordBohr atom, American Journal of Physics 49, 1981 https://aapt.scitation.org/doi/abs/10.1119/1.12521
Olszewski, Stanisaw, 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
Follow Tereza Putarova on Twitter at @TerezaPultarova. Follow us on Twitter @Spacedotcom and on Facebook.
Read more here:
The Bohr model: The famous but flawed depiction of an atom - Space.com
- Physicists breed Schrdinger's cats to find boundaries of the | Cosmos - Cosmos [Last Updated On: May 3rd, 2017] [Originally Added On: May 3rd, 2017]
- The application of three-axis low energy spectroscopy in quantum physics research - Phys.Org [Last Updated On: May 3rd, 2017] [Originally Added On: May 3rd, 2017]
- Scientists 'BREED' Schrodinger's Cat in massive quantum physics breakthrough - Express.co.uk [Last Updated On: May 3rd, 2017] [Originally Added On: May 3rd, 2017]
- Quantum Physics: Are Entangled Particles Connected Via An Undetected Dimension? - Forbes [Last Updated On: May 3rd, 2017] [Originally Added On: May 3rd, 2017]
- The World Of Quantum Physics: EVERYTHING Is Energy : In5D ... [Last Updated On: May 3rd, 2017] [Originally Added On: May 3rd, 2017]
- Introduction to quantum mechanics - Wikipedia [Last Updated On: May 3rd, 2017] [Originally Added On: May 3rd, 2017]
- A general election, like quantum physics, is a thing of waves and particles - The Tablet [Last Updated On: May 4th, 2017] [Originally Added On: May 4th, 2017]
- 14-Year-Old Earns Physics Degree From TCU CBS Dallas / Fort ... - CBS DFW [Last Updated On: May 11th, 2017] [Originally Added On: May 11th, 2017]
- Quantum Entanglement Persists Even Under High Accelerations ... - International Business Times [Last Updated On: May 11th, 2017] [Originally Added On: May 11th, 2017]
- Quantum Entanglement Persists Even Under High Accelerations, Experiments Reveal - International Business Times [Last Updated On: May 11th, 2017] [Originally Added On: May 11th, 2017]
- Quantum - Wikipedia [Last Updated On: May 11th, 2017] [Originally Added On: May 11th, 2017]
- Unbreakable quantum entanglement - Phys.Org [Last Updated On: May 11th, 2017] [Originally Added On: May 11th, 2017]
- Physics may bring faster solutions for tough computational problems - Phys.Org [Last Updated On: May 14th, 2017] [Originally Added On: May 14th, 2017]
- UBC researchers propose answer to fundamental space problem - CBC.ca [Last Updated On: May 17th, 2017] [Originally Added On: May 17th, 2017]
- Quantum Biology and the Frog Prince - ScienceBlog.com (blog) [Last Updated On: May 18th, 2017] [Originally Added On: May 18th, 2017]
- The Marriage Of Einstein's Theory Of Relativity And Quantum Physics Depends On The Pull Of Gravity - Forbes [Last Updated On: May 18th, 2017] [Originally Added On: May 18th, 2017]
- New Research May Reconcile General Relativity and Quantum Mechanics - Futurism [Last Updated On: May 18th, 2017] [Originally Added On: May 18th, 2017]
- The Bizarre Quantum Test That Could Keep Your Data Secure - WIRED [Last Updated On: May 20th, 2017] [Originally Added On: May 20th, 2017]
- Testing quantum field theory in a quantum simulator - Phys.org - Phys.Org [Last Updated On: May 20th, 2017] [Originally Added On: May 20th, 2017]
- A classic quantum test could reveal the limits of the human mind - New Scientist [Last Updated On: May 20th, 2017] [Originally Added On: May 20th, 2017]
- Teleportation Could Be Possible Using Quantum Physics - Futurism - Futurism [Last Updated On: May 22nd, 2017] [Originally Added On: May 22nd, 2017]
- Nobel winner to talk cats, computers and quantum physics - AroundtheO [Last Updated On: May 23rd, 2017] [Originally Added On: May 23rd, 2017]
- Could Ant-Man Beat Superman With Quantum Physics? - Heroic Hollywood (blog) [Last Updated On: May 26th, 2017] [Originally Added On: May 26th, 2017]
- Physicists Discover Geometry Underlying Particle Physics [Last Updated On: May 26th, 2017] [Originally Added On: May 26th, 2017]
- Home - Center for Quantum Activism [Last Updated On: May 26th, 2017] [Originally Added On: May 26th, 2017]
- Physics - Wikipedia [Last Updated On: May 26th, 2017] [Originally Added On: May 26th, 2017]
- What Quantum Physics Can Tell Us about the Afterlife ... [Last Updated On: May 26th, 2017] [Originally Added On: May 26th, 2017]
- A Quantum Physicist Explains How Ant-Man Can Beat Superman - Inverse [Last Updated On: May 28th, 2017] [Originally Added On: May 28th, 2017]
- Academic Journal: Quantum Physics Is 'Oppressive' to Marginalized People - National Review [Last Updated On: May 30th, 2017] [Originally Added On: May 30th, 2017]
- University of Arizona Scholar Creates a Feminist Brand of Physics to ... - Breitbart News [Last Updated On: June 1st, 2017] [Originally Added On: June 1st, 2017]
- Feminist Launches 'Intersectional Quantum Physics' to End Newton's 'Oppression' - PJ Media [Last Updated On: June 1st, 2017] [Originally Added On: June 1st, 2017]
- In atomic propellers, quantum phenomena can mimic everyday ... - Phys.Org [Last Updated On: June 1st, 2017] [Originally Added On: June 1st, 2017]
- Quantum physics is oppressive - Patheos - Patheos (blog) [Last Updated On: June 5th, 2017] [Originally Added On: June 5th, 2017]
- It's widely abused as a buzzword. But can quantum mechanics explain how we think? - National Post [Last Updated On: June 5th, 2017] [Originally Added On: June 5th, 2017]
- Quantum Physics and Love are Super Weird and Confusing, but This Play Makes Sense of Them Both - LA Magazine [Last Updated On: June 6th, 2017] [Originally Added On: June 6th, 2017]
- One step closer to the quantum internet by distillation - Phys.Org [Last Updated On: June 7th, 2017] [Originally Added On: June 7th, 2017]
- Solving systems of linear equations with quantum mechanics - Phys.Org [Last Updated On: June 10th, 2017] [Originally Added On: June 10th, 2017]
- Neural networks take on quantum entanglement - Phys.Org [Last Updated On: June 14th, 2017] [Originally Added On: June 14th, 2017]
- Chinese satellite breaks a quantum physics record, beams entangled photons from space to Earth - Los Angeles Times [Last Updated On: June 15th, 2017] [Originally Added On: June 15th, 2017]
- Cybersecurity Attacks Are a Global Threat. Chinese Scientists Have the Answer: Quantum Mechanics - Newsweek [Last Updated On: June 16th, 2017] [Originally Added On: June 16th, 2017]
- New Quantum-Entanglement Record Could Spur Hack-Proof Communications - Yahoo News [Last Updated On: June 18th, 2017] [Originally Added On: June 18th, 2017]
- What Is Quantum Mechanics? - livescience.com [Last Updated On: June 18th, 2017] [Originally Added On: June 18th, 2017]
- China sets new record for quantum entanglement en route to build new communication network - NEWS.com.au [Last Updated On: June 19th, 2017] [Originally Added On: June 19th, 2017]
- Physicists Demonstrate Record Breaking Long-Distance Quantum Entanglement in Space - Futurism [Last Updated On: June 21st, 2017] [Originally Added On: June 21st, 2017]
- Viewpoint: A Roadmap for a Scalable Topological Quantum Computer - Physics [Last Updated On: June 22nd, 2017] [Originally Added On: June 22nd, 2017]
- How Schrdinger's Cat Helps Explain the New Findings About the Quantum Zeno Effect - Futurism [Last Updated On: June 22nd, 2017] [Originally Added On: June 22nd, 2017]
- BMW and Volkswagen Try to Beat Apple and Google at Their Own Game - New York Times [Last Updated On: June 23rd, 2017] [Originally Added On: June 23rd, 2017]
- How quantum physics could revolutionize casinos and betting if you can understand it - Casinopedia [Last Updated On: June 23rd, 2017] [Originally Added On: June 23rd, 2017]
- Quantum thermometer or optical refrigerator? - Phys.org - Phys.Org [Last Updated On: June 23rd, 2017] [Originally Added On: June 23rd, 2017]
- Atomic imperfections move quantum communication network closer ... - Phys.Org [Last Updated On: June 24th, 2017] [Originally Added On: June 24th, 2017]
- DoE Launches Chicago Quantum Exchange - HPCwire (blog) [Last Updated On: June 26th, 2017] [Originally Added On: June 26th, 2017]
- Google to Achieve "Supremacy" in Quantum Computing by the End of 2017 - Big Think [Last Updated On: June 26th, 2017] [Originally Added On: June 26th, 2017]
- Physicists settle debate over how exotic quantum particles form - Phys.Org [Last Updated On: June 27th, 2017] [Originally Added On: June 27th, 2017]
- Physicists make quantum leap in understanding life's nanoscale machinery - Phys.Org [Last Updated On: June 27th, 2017] [Originally Added On: June 27th, 2017]
- How quantum trickery can scramble cause and effect - Nature.com [Last Updated On: June 28th, 2017] [Originally Added On: June 28th, 2017]
- Berkeley Lab Intern Finds Her Way in Particle Physics | Berkeley Lab - Lawrence Berkeley National Laboratory [Last Updated On: June 28th, 2017] [Originally Added On: June 28th, 2017]
- Quantum Physics News - Phys.org - News and Articles on ... [Last Updated On: June 28th, 2017] [Originally Added On: June 28th, 2017]
- Quantum computers are about to get real - Science News Magazine [Last Updated On: June 29th, 2017] [Originally Added On: June 29th, 2017]
- Physics4Kids.com: Modern Physics: Quantum Mechanics [Last Updated On: June 29th, 2017] [Originally Added On: June 29th, 2017]
- Payments Innovation - A Quantum World Of Payments - Finextra (blog) [Last Updated On: June 30th, 2017] [Originally Added On: June 30th, 2017]
- Why can't quantum theory and relativity get along? - Brantford Expositor [Last Updated On: June 30th, 2017] [Originally Added On: June 30th, 2017]
- New method could enable more stable and scalable quantum computing, physicists report - Phys.Org [Last Updated On: June 30th, 2017] [Originally Added On: June 30th, 2017]
- Telecommunications, Meet Quantum Physics - Electronics360 [Last Updated On: June 30th, 2017] [Originally Added On: June 30th, 2017]
- How young is too young to talk to kids about science? Never, says one quantum physicist - ABC Local [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- Supercool breakthrough brings new quantum benchmark - Phys.org - Phys.Org [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- Physics For Toddlers . News | OPB - OPB News [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- Quantum Physics Provide Evidence that the Future Influences the Past - Edgy Labs (blog) [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- This quantum theory predicts that the future might be influencing the ... - ScienceAlert [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- Physicists May Have Discovered One of the Missing Pieces of Quantum Theory - Futurism [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- Something New For Baby To Chew On: Rocket Science And ... - NPR - NPR [Last Updated On: July 9th, 2017] [Originally Added On: July 9th, 2017]
- A New Quantum Theory Predicts That the Future Could Be Influencing the Past - Big Think [Last Updated On: July 14th, 2017] [Originally Added On: July 14th, 2017]
- Basic Assumptions of Physics Might Require the Future to Influence ... - Gizmodo [Last Updated On: July 14th, 2017] [Originally Added On: July 14th, 2017]
- Scientists teleport particle into space in major breakthrough for quantum physics - The Independent [Last Updated On: July 14th, 2017] [Originally Added On: July 14th, 2017]
- Rockstar scientist David Reilly takes the axe to quantum physics - The Sydney Morning Herald [Last Updated On: July 14th, 2017] [Originally Added On: July 14th, 2017]
- Quantum Mechanics Could Shake Up Our Understanding of Earth's ... - Gizmodo [Last Updated On: July 14th, 2017] [Originally Added On: July 14th, 2017]
- The Standard Model of particle physics is brilliant and completely flawed - ABC Online [Last Updated On: July 17th, 2017] [Originally Added On: July 17th, 2017]
- Quantum mechanics inside Earth's core - Phys.org - Phys.Org [Last Updated On: July 17th, 2017] [Originally Added On: July 17th, 2017]
- Making a quantum leap in space research - Shanghai Daily (subscription) [Last Updated On: August 6th, 2017] [Originally Added On: August 6th, 2017]
- Unlocking the Secrets of Quantum Physics to Create New Materials - Yu News (blog) [Last Updated On: August 6th, 2017] [Originally Added On: August 6th, 2017]
- China's Silicon Valley aims to become the country's top research center - Abacus [Last Updated On: October 16th, 2019] [Originally Added On: October 16th, 2019]