Questions tagged [quantum-chemistry]
Quantum chemistry is a subfield of quantum mechanics. Like its parent field, quantum chemistry focuses on understanding physical phenomena occuring at the atomic scale. Quantum chemistry however is more focused on providing useful descriptions of electronic structure to aid in understanding chemical problems (e.g. reactions, spectra, dynamics, ...).
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Why is the 2s orbital lower in energy than the 2p orbital when the electrons in 2s are usually farther from the nucleus?
My chemistry book explains that even though electrons in the $\mathrm{2p}$ orbital are closer to the nucleus on average, electrons from the $\mathrm{2s}$ orbital spend a very short time very close to ...
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How can antibonding orbitals be more antibonding than bonding orbitals are bonding?
In molecular orbital theory, the fact that a bonding and antibonding molecular orbital pair have different energies is accompanied by the fact that the energy by which the bonding is lowered is less ...
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What is the inert pair effect?
I was reading about the p-block elements and found that the inert pair effect is mentioned everywhere in this topic. However, the book does not explain it very well. So, what is the inert pair effect? ...
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Difference between shells, subshells and orbitals
What are the definitions of these three things and how are they related? I've tried looking online but there is no concrete answer online for this question.
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Can hot food ever emit x-rays or gamma rays?
I was just wondering, if heating food up is the result of increasing the energy of bends and stretches in the bonds of the molecules, is it ever possible for tiny amounts of x-rays and gamma rays be ...
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Pauli exclusion principle and resonance
I've always been a bit uncomfortable with the concept of more than two electrons in a single orbital-like region(probability-wise) which occurs in resonance.
This seems to disobey Pauli's exclusion ...
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Is there an energy cost associated with flipping the spin of an electron?
THE STORY:
A common example used to illustrate the limitations of restricted Hartree-Fock (RHF) theory is the H$_2$ dissociation energy ($D_e$) curves. RHF enforces electrons to be paired into spin ...
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Acidity of substituted phenols
Phenol has a $\mathrm pK_\mathrm a$ approximately equal to $9.9$.
When one studies the acidity of chlorophenols, one notices the following:
First of all, chlorophenols are more acidic than phenol, ...
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What is the exchange interaction?
As the wikipedia article for the exchange interaction so aptly notes, exchange "has no classical analogue."
How wonderful.
Exchange shows up essentially while enforcing the condition that two ...
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Sp5 hybridization in cyclopropane?
I have never before heard/read about something as a $sp^5$ hybridization. Today, Henry Rzepa's blog post made me aware of the existance of such a bonding system. That made me search a little bit and I ...
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What is the physical basis for Hund's first rule?
According to Hund's first rule, a set of degenerate orbitals are singly occupied first, before the second slot in any of the orbitals are populated. This is quite intuitive because electron-electron ...
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Why are covalent bonds directional?
It is said that covalent bonds are directional, while ionic bonds are not. Why? Is it because of the orientation/directional properties of the overlapping orbitals?
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Why are noble gases stable
I was recently asked the question "Why are noble gases stable? with the expectation of providing an answer beyond the general explanation of "they have full valence layers" and I couldn't think of one....
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Why do atoms "want" to have a full outer shell?
Okay, so I know that this is about filling the orbitals of the atom, and I understand that. What I don't understand is why? For example, an Oxygen atom has 8 protons and 8 electrons spinning around it....
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Imaginary Bonding Interactions
Usually in chemistry, we deal with bonding interactions. That is, if I have the diatomic A-A molecule or A-B molecule, there's a favorable interaction (i.e., a bond) and a prototypical MO diagram like ...
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