31
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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 ...
- 71.1k
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 ...
- 31k
22
votes
Accepted
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 ...
- 4,855
22
votes
Accepted
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 ...
- 27.7k
22
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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 ...
- 38.9k
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 ...
- 12.9k
19
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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 ...
- 12.9k
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 ...
- 40.2k
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 ...
- 39k
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 ...
- 482
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 ...
- 37.4k
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 ...
- 2,396
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 ...
- 31k
15
votes
Can an atom have more than 8 valence electrons? If not, why is 8 the limit?
Why 8? has not really been addressed by the above answers, and while tangential to the question, it is somewhat important to be considered. In general, but not always, atoms react to form complete ...
- 6,596
15
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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 ...
- 4,709
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 ...
- 18.9k
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 ...
- 35.4k
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 ...
- 38.9k
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 ...
- 71.1k
12
votes
What is the reason for the blue color of an ammoniated electron?
Both of your questions could benefit from more background, so please forgive me if I understood something wrong. However, I'll try to answer as best I can:
The excess electron in liquid ammonia is ...
- 554
12
votes
What is the reason for the blue color of an ammoniated electron?
To expand on Thawn's answer to #1 a bit:
In quantum systems, a particle is bound to discrete states when it is constrained by a sufficiently deep potential well; otherwise its energy is continuous$^\...
- 17.3k
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.
...
- 18.6k
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 ...
- 30k
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 ...
- 17.3k
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 ...
- 17.3k
11
votes
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Why do electrons need to be paired?
Wouldn’t it better to just fill them up with single electrons, as per
Hund’s rule, and then leave them like that? Would that not be more
energetically favorable?
You have to consider two ...
- 18.9k
11
votes
Why does the two-electron exchange integral in Hartree-Fock theory have positive values?
The conclusion seems obvious but I just cannot find a proof.
No, I don't think it is obvious. At least I could not think about a simple algebraic proof that the exchange integral $\langle ab \vert ba ...
- 18.9k
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 ...
- 42.6k
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,...
- 12.9k
11
votes
Accepted
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 ...
- 11.6k
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