Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and the processes by which these arrangements change. This includes ions as well as neutral atoms and, ...

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Why do electrons occupy the space around nuclei, and not collide with them?

We all learn in grade school that electrons are negatively-charged particles that inhabit the space around the nucleus of an atom, that protons are positively-charged and are embedded within the ...
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Why doesn't matter pass through other matter if atoms are 99.999% empty space?

The ghostly passage of one body through another is obviously out of the question if the continuum assumption were valid, but we know that at the micro, nano, pico levels (and beyond) this is not even ...
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Why are most metals gray/silver?

Why do most metals (iron, tin, aluminum, lead, zinc, tungsten, nickel, etc.) appear silver or gray in color? (What atomic characteristics determine the color?) What makes copper and gold have ...
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Where did Schrödinger solve the radiating problem of Bohr's model?

One of the problems with Bohr's theory to describe the hydrogen atom, was that the electron orbiting around the nucleus has an acceleration. Therefore it radiates and loses energy, until it would ...
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Does an electron move from one excitation state to another, or jump?

I'm wondering, when an electron changes state, does it move from one state to another over some (very small) time period? Or does it change from one state to another in no time? If the former, what ...
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How do electrons jump orbitals?

My question isn't how they receive the energy to jump, but why. When someone views an element's emission spectrum, we see a line spectrum which proves that they don't exist outside of their orbitals (...
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If photon energies are continuous and atomic energy levels are discrete, how can atoms absorb photons?

If photon energies are continuous and atomic energy levels are discrete, how can atoms absorb photons? The probability of a photon having just the right amount of energy for an atomic transition is $0$...
10
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921 views

Trouble understanding the Bohr model of the atom

In this article it says: The electrons can only orbit stably, without radiating, in certain orbits (called by Bohr the "stationary orbits") at a certain discrete set of distances from the nucleus. ...
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How do photons know they can or can't excite electrons in atoms?

This might be a stupid question, but nonetheless, it has been bothering me. If you take a photon, make it go through some atoms in a solid, liquid or whatever, then you have the chance of this photon ...
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408 views

How to distinguish between the spectrum of an atom in motion and the one of a scaled atom?

Galaxies are moving dragged by the space expansion. When atoms are in motion the doppler effect will shift the spectra of the emitted photons. The proton-to-electron mass ratio, $\frac{m_e}{m_p}$ ...
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Huge confusion with Fermions and Bosons and how they relate to total spin of atom

I am supremely confused when something has spin or when it does not. For example, atomic Hydrogen has 4 fermions, three quarks to make a proton, and 1 electron. There is an even number of fermions, ...
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Why is the sky never green? It can be blue or orange, and green is in between!

I, like everybody I suppose, have read the explanations why the colour of the sky is blue: ... the two most common types of matter present in the atmosphere are gaseous nitrogen and oxygen. ...
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Which experiments prove atomic theory?

Which experiments prove atomic theory? Sub-atomic theories: atoms have: nuclei; electrons; protons; and neutrons. That the number of electrons atoms have determines their relationship with other ...
5
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3answers
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What keeps electrons in an atom from flying away or falling into the nucleus?

In atoms, what force or charge, etc. keeps electrons from flying away or into their nucleus? is there a kind of weak-force at work on the atomic scale? Note I am aware the electron positions are ...
2
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4answers
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What is wrong with the Bohr model?

What is wrong about the Bohr model? Many books say it is wrong but doesn't say why and I don't know why.
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Why is the Bohr's idea of defined circular orbits overruled?

If we consider a thought experiment for determining position of an electron by using photons of light. According to principles of optics, if we use light of wavelength $\lambda$, then the position of ...
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4answers
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Lasing in a 2-Level system?

What exactly is the difference between 2-Level, 3-Level and 4-Level systems? Why can we not achieve stimulated emission in a two-level system using optical pumping?
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6answers
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Why can't electrons fall into the nucleus?

I read a book on pop sci book on quantum mechanics and the author said that electrons do not fall into the nucleus due to quantum mechanics- which principles suggest this (I think it was Heisenberg's ...
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Why is the nucleus so small and why is the atom 99.999% empty space?

A nucleus consists of protons and neutrons. Both are extremely heavy compared to electrons. Then how come they are contained within an extremely tiny space? And why does the atom consist of 99.999% ...
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Why do non-hydrogen atomic orbitals have the same degeneracy structure as hydrogen orbitals?

The solutions of the Schrödinger equation for hydrogen are the "electronic orbitals", shown in this picture: (source) They have the following degeneracy structure: (source) It is often said that ...
17
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Does the mass of an electron change with its “energy state”?

When an electron absorbs a photon, it gets into a higher energy state and goes into the upper orbit/shell. Does (rather should) this absorption of energy also have an impact on its mass (although ...
8
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2answers
181 views

Is this a correct demonstration for why elements above untriseptium cannot exist?

With the confirmation that elements 113, 115, 117, and 118 are indeed fundamental elements that are now to be named on the periodic table, the next question is: what is the highest atomic number ...
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4answers
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Why are hydrogen energy levels degenerate in $\ell$ and $m$?

Is there a good physical picture of why the energy levels in a hydrogen atom are independent of the angular momentum quantum number $\ell$ and $m$?
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How would one detect antihydrogen in the universe?

Since the spectra of hydrogen and antihydrogen are the same, how do astronomers know which one they're detecting? Is, perhaps, the Lamb shift in antihydrogen different?
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Atomic Physics: stimulated emission

I'm studying a chapter about atomic physics right now but there's thing I just don't seem to understand. When stimulated emission occurs, there's an incoming photon which stimulates the atom to go an ...
3
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0answers
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Quantum mechanics,and how the law $ΔxΔp≥ℏ/2$ explains the paradox regarding atoms [duplicate]

In Chapter 2-3,Vol I of the Feynman lectures, Feynman talks about a rule in quantum mechanics that says that one cannot know both where something is and how fast it is moving. That the uncertainty of ...
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The Quantization of Photon Energies [duplicate]

Despite Planck's constant being in $E=hf$, it would appear to me that energy is still not discrete, as frequency can be an fraction of a Hertz that one wants. How does this imply that electromagnetic ...
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337 views

Principle of Reflection on atomic level

The well observed phenomenon has besides several others has always been a fascination to me, we are well aware of several theories, experiments and practical applications of the well known phenomenon. ...
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1answer
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Why do most metals appear silver in color with gold being an exception from a scattering and EM viewpoint?

Related: Why are most metals gray/silver? After reading Johannes’ impressive answer to Ali Abbasinasab question of why do most metals appear silver in color with the exception of gold (and copper), ...
12
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2answers
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If atoms never “physically” touch each others, then how does matter-antimatter annihilation happen?

It is known that matter and antimatter annihilate each other when they "touch" each other. And as far as I know, the concept of "touching" as our brain gets it is not true on the atomic level since ...
10
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3answers
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What's is the origin of Orbital Angular Momentum of electrons in atoms?

Consider the Hydrogen 1s electron. We know that, in the quantum picture, the electron isn't orbiting or rotating at all, rather we simply state that the electron is spread over the entire space with ...
8
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3answers
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Is there only radial motion in the Hydrogen ground state?

The ground state of the Hydrogen atom is spherically symmetric. In other words, the wave function Psi depends only on the distance r of the electron from the nucleus. As a consequence all ...
3
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4answers
359 views

How to explain what an electron is to someone new to physics? [closed]

I've got asked by someone who just graduated school and is about to start studying physics, what exactly is an electron, if it is not "a small ball rotating around the core of an atom". I couldn't ...
5
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1answer
89 views

What do term symbols with a half-integer “$L$” like $^3[3/2]_{1/2}$ mean?

Atomic term symbols are used to notate the angular momentum content of the electronic states of an atom, and are normally written down as $$^{2S+1}L_J$$ where the state has total spin $S$, spin ...
4
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439 views

How big is an excited hydrogen atom?

Suppose an empty universe with the exception of a single hydrogen atom (1 proton, 1 electron). The electron may be in its ground state or it may be excited a certain number of levels. Suppose it is at ...
4
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1answer
35 views

Do any elements form stable doubly-charged negative ions?

It is perfectly possible for an atom - particularly on the electronegative end of the periodic table to form negatively-charged ions by attracting an electron, and these species can be stable, ...
4
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2answers
192 views

Is fluorescence from a single atom/ion visible with the naked eye (e.g. in a strongly coupled trap or cavity)

I remember sitting in on a conference talk by a person (possibly Rainer Blatt) doing research with trapped ions (or single atoms strongly coupled to light in an optical cavity), and the person showed ...
3
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2answers
642 views

An electron in $s$ state

If an electron is in $s$ state, for example in 1s state for Hydrogen or 5s state for Silver atom, $\ell=0$. So,its total angular momentum $L$ is also equal to 0. So, what is electron actually doing in ...
2
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1answer
9k views

What prevents an atom's electrons from “collapsing” onto its protons? [duplicate]

Forgive me if the answer to this is obvious. I have no formal physics training, and I remember that when I asked my physics teacher this, she just frowned and said "Good question." An electron is ...
2
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1answer
206 views

Does there exist electric field around all the substances?

A system of two equal and opposite charges separated by a certain distance is called an electric dipole. Electric dipole moment ($p$) is defined as the product of either charge ($q$) and the ...
0
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198 views

What is the correct theoretical formula for the hyperfine splitting of neutral hydrogen (21cm line)

I found two different expressions to express the energy splitting of the hyperfine transition of neutral hydrogen (21 cm line, HI) that are not equivalent, imo. From Wolfram ScienceWorld: $$\...
9
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2answers
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Is Palladium an exception?

I have been taught in school that atoms cannot have more than 8 electrons in the outer shell. Palladium atom's electron configuration is 2,8,18,18. Why isn't it 2,8,18,17,1 like the case of Platinum 2,...
3
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0answers
135 views

What are the assumptions behind “term symbols”?

In multi-electron atoms, the electronic state of the optically active "subshell" is often expressed in "term symbols" notation. I.e. $^{2S+1}L_J$. This presumes that the system of electrons has ...
2
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3answers
167 views

Quantum mechanics scattering theory

When an electron absorbs energy and jumps to the another excited state by absorbing the photon and why it is always said that the electron will come back to $\hbar\omega/2$? Why doesn't the electron ...
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2answers
96 views

Atomic Clocks: How is time measured?

I am trying to understand atomic clocks better. I am not getting HOW the cesium oscillation is actually being counted. So from my understanding of an older atomic clock: cesium gets heated-> ...
1
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1answer
109 views

friction on atomic scale

I am getting into friction on an atomic scale. For instance, take two rigid layers of atoms of the kind A that are placed on top of each other, just like putting two boards of wood on top of each ...
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2answers
2k views

Book recommendation for Atomic & Molecular physics

What are some interesting books for a sophomore undergrad about Atomic & Molecular Physics?
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What is meant by an excited atom?

I want to know how an atom is when it is excited. If an atom, due to collision of another fast moving atom, becomes fast moving as well, is that also an "excited state"?
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How is the speed of light an absolute maximum speed in the universe? [closed]

Under the heading which came first, the chicken or the egg, which came first: the maximum velocity of electrons orbiting the atom, or the speed of light as the maximum velocity limit? Is it possible ...
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How can we be sure about the constancy of atomic clocks as in the Hafele and Keating time dilation test?

Atomic clocks were used in Hafele and Keatings experiment which supposedly helped to prove time dilation. Time Dilation Proof - Hafele and Keating How can we be sure other forces didn't act upon the ...