31 votes

What is the physical basis for Hund's first rule?

Disclaimer My following answer is the "traditional" explanation of Hund's first rule, which is based on a smaller value of $V_\mathrm{ee}$ (electron-electron repulsions) in the triplet state arising ...
orthocresol's user avatar
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26 votes

What happens when an electron in a metal is excited?

You seem to be misunderstanding what is a "sea of electrons". In fact, this is a metaphor upon a metaphor upon an abstraction. There is no sea. There is a huge bunch of orbitals. (Sure, the solid ...
Ivan Neretin's user avatar
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23 votes
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Do Electrons Really 'Spin'?

It depends on what you mean by "spin". If you mean "have intrinsic internal angular momentum, independent of its trajectory through space", then yes, electrons spin, and that's what the quantum ...
R.M.'s user avatar
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22 votes
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What is the physical basis for Hund's first rule?

The lowest energy state has parallel spins to maximize the exchange energy. As you say, there's a Coulomb repulsion between two electrons to put them in the same orbital. There's also a quantum ...
Geoff Hutchison's user avatar
22 votes
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True or false: "A used AA battery contains fewer moles of electrons than a new AA battery."

Very bad explanation in the email response. The explanation reads.. "Thus, the battery has the same number of protons and neutrons, but less electrons. This also means more unreactive metal ...
AChem's user avatar
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21 votes
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How to think of solvated electrons?

The analogy with a proton is actually a good one if you are careful to remember that an electron is nearly 2000 times lighter than a proton. What does that mean? It means that despite the fact that an ...
jheindel's user avatar
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19 votes
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What is happening in this video of solvated electrons donated from sodium in ammonia?

I'll try an answer to this question because I watched this video a while back and did a bit of reading on it at the time and I think I understand the big picture. The problem is that these solvated ...
jheindel's user avatar
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18 votes

Do electrons have some volume, area or shape?

Quoting from the Nobel lecture of Hans G. Dehmelt (1989): With the rise of Dirac’s theory of the electron in the late twenties their size shrunk to mathematically zero. Everybody “knew” then ...
DavePhD's user avatar
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18 votes

Which atom is the smallest atom?

The volumes of the nuclei are negligible compared to the atomic radii (like a "pea in a soccer/football/cricket stadium"). The higher the nuclear charge, the closer the electrons to the ...
Karsten's user avatar
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17 votes
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Do electrons have some volume, area or shape?

Atoms are composed of a positively charged nucleus and an outer shell of negatively charged electrons. When two atoms come into close proximity, their electron shells repel, preventing the atoms from ...
Acccumulation's user avatar
17 votes
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What is the unit of Z effective?

This is an example of terminology which should be taken with a grain of salt. The term "effective nuclear charge" is often casually symbolized with $Z_\mathrm{eff}.$ This is a universally ...
andselisk's user avatar
  • 37.6k
16 votes

Why do electrons jump back after absorbing energy and moving to a higher energy level?

This is a very fundamental question and for really understanding the "why" some advanced physics is involved. I will describe the process rather superficially. As you might know, the level ...
Paul's user avatar
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16 votes

Why is it that protons and electrons undergo the same amount of deflection in an electric field if they have the same energy?

Now that's a mildly non-trivial observation. Why would they be equal, really? Let's say a particle with mass $m$, charge $q$, and initial velocity $v$ enters an area of length $L$ where an electric ...
Ivan Neretin's user avatar
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15 votes
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While filling electrons, we follow Aufbau principle, but not while removing them. Why is this so?

Usually when adding electrons based on the Aufbau principle, you go from one element to the next highest one, e.g. from $\ce{Ti}: \ce{[Ar] 4s^2 3d^2}$ to $\ce{V: [Ar] 4s^2 3d^3}$. Thus you add not ...
Feodoran's user avatar
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15 votes
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Why is the electron-nucleus attraction modelled with only electrostatic interactions?

If I understand the question correctly, OP is somewhat surprised that Coulomb's law is used to describe the interaction between an electron and a nucleus, although it is usually pictured that ...
Wildcat's user avatar
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14 votes
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Why are dipoles "permanent/induced dipole permanent/induced dipole" and not just "permanent/induced dipole" once?

Because it takes two to tango. Dipoles interact with each other. A Lone dipole has nothing to interact with (other than an electric field, but if we ignore some externally applied macro field, there ...
matt_black's user avatar
14 votes
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Why does the same electron transition release photons of different frequencies for some elements?

I am glad that you updated the question because it highlights a very common misconception. First of all the JavaLab Flame Test is completely wrong for both copper, calcium and many more salts ...
AChem's user avatar
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13 votes
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How does an electrons's wave function change when it moves between energy levels?

You need to go back to the very start. Here, you're kind of asking: I have a solution $\psi_0$, how do I get the next solution $\psi_1$? The answer is to look at how $\psi_0$ was obtained, and it ...
orthocresol's user avatar
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12 votes

Do Electrons Really 'Spin'?

Despite the success of the Schrödinger Equation in predicting energy levels of the hydrogen atom, experimental observations suggest that it doesn't tell the whole story of electron behavior in atoms. ...
paracetamol's user avatar
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12 votes

What is the physical basis for Hund's first rule?

Some understanding can be gained by looking at the symmetry of the orbital parts of the wavefunctions involved. The total wavefunction for electrons must be anti-symmetric with respect to exchanging ...
porphyrin's user avatar
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12 votes
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Precise definition of atomic orbital

In school I was taught that an atomic orbital is the 3-dimensional region in which the electron is located with a probability of 90%. This is not correct. An atomic orbital is a solution to ...
Zhe's user avatar
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12 votes
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How to determine the angle between non-bonding electron pairs?

Yes, there are ways one could claim to calculate an angle between two non-bonding electron pairs. BUT: As Mithoron points out, this Chem.SE question illustrates how quantum chemical calculations and ...
hBy2Py's user avatar
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11 votes
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Can an ion isotope exist?

Short answer: Yes. Longer answer: Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei. Everything else about them is the same. The numbers of protons and ...
Ben Norris's user avatar
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11 votes

Confusion on light absorption by electrons

Depending on how large the value $y$ is, the premise of your question can be wrong. On the other hand, if you jump between two electronic energy levels where $y$ is on the order of vibrational states,...
jheindel's user avatar
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11 votes
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Magnetic moment μ approximation

I think you can come at this approximation in two ways. Using more advance methods, the approximation is obtained as a truncation of the Laurent series of $\sqrt{x(x+2)}$ about $x=\infty$. This is ...
Tyberius's user avatar
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11 votes

Isn't the dual behaviour of subatomic particles contradictory?

Take a nice simple system like a hydrogen molecule. It's true that the two electrons repel each other, but at the same time they are attracted by the positive charge of the two protons. If we start ...
John Rennie's user avatar
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11 votes
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Difference between spin-orbit coupling and the Russell-Saunders Effect?

I'm not aware of the Russell–Saunders effect, but the Russell–Saunders coupling scheme is definitely a thing. As you noted, the Wikipedia page on "spin-orbit interaction" doesn't talk about ...
orthocresol's user avatar
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11 votes
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Can a metal be forced to form an anion theoretically?

Absolutely! You will find these mostly in electride systems and off these, mostly in alkali metals. Here is an example research paper: "Superakali-Alkalide Interactions and Ion Pairing in Low-...
Evamentality's user avatar
11 votes
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Can an electron be excited to a spin state with s ≠ 1/2?

The major mistake is considering a nucleus like if it were an elementary particle. Compare a nucleus spin configuration to spin electronic configuration of atoms. In both cases, there are multiple ...
Poutnik's user avatar
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10 votes
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What chemical properties that allow for colour exist in the dark?

The chemical property that creates colour is the ability to absorb light of a specific visible wavelength. There is more than one way to do this. Mostly colour is caused by the existence of ...
matt_black's user avatar

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