40
votes
Can an atom bond with more than 8 other atoms?
Yes, there are coordination complexes of large elements which have coordination numbers greater than eight. Some examples are:
$\ce{[ReH9]^2-}$ with a tricapped trigonal prismatic structure. The nine ...
- 15.2k
31
votes
Can an atom bond with more than 8 other atoms?
14 coordination is claimed in $\ce{U(BH4)4}$ (ref_1, p. 268). The molecule exists as a polymer in the solid state. Six hydrogens from two of the $\ce{BH4}$ groups bond between the boron and uranium (...
- 83.4k
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 ...
- 69.6k
24
votes
Molecular orbital (MO) diagram for N2 and N2^-
I have been taught that the MO diagram is different for molecules with
14 or less electrons than the one used for molecules with 15 or more
electrons.
This is (partly) wrong because the change in ...
- 18.7k
23
votes
Accepted
Will adding up protons and electrons (without neutrons) create a new element?
Yes and no.
Elements are defined by the number of protons only. It does not matter if (say) a carbon nucleus has six or seven (or eight) neutrons, they will all react the same.*
With that, to create ...
- 66k
22
votes
What is SPDF configuration?
s, p, d, f and so on are the names given to the orbitals that hold the electrons in atoms. These orbitals have different shapes (e.g. electron density distributions in space) and energies (e.g. 1s is ...
- 83.4k
22
votes
Which relatively simple molecules violate the octet rule?
There are 3 types of octet rule "violations" or exceptions
molecules with an odd number of electrons, such as nitric oxide
(image source)
molecules with less than 8 electrons around an atom, $\ce{...
- 83.4k
22
votes
Accepted
Why do 3d orbitals have lesser energy than 4s orbitals in transition metals?
Disclaimer: I now believe this answer to be fully incorrect.
Please consider un-upvoting it and/or downvoting it. I do not like seeing incorrect answers at +22.
However, I will leave it up ...
- 69.6k
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 ...
- 27.5k
22
votes
Accepted
Why are protons more common than hydride ion?
This is because we live in a world dominated by oxygen and water. In other words, it is an oxidized world. Most metals occur naturally in the form of oxides, silicates, halides, or other derivatives. ...
- 30.5k
21
votes
Accepted
Difference between Coupled Cluster and Full CI
Full Coupled Cluster (FCC) vs. Full Configuration Interaction (FCI)
The main theoretical difference is the way excitations are used. "Excitation" refers to putting one or more electrons in higher ...
- 6,819
21
votes
Accepted
Degeneracy of second excited state of H-?
I think it is important to understand that for hydrogen atom (or any other one-electron system) all orbitals from the same shell have same energy. For instance, $E_\mathrm{2s} = E_\mathrm{2p}$, $E_\...
- 18.7k
20
votes
Will adding up protons and electrons (without neutrons) create a new element?
Jan's answer is correct. I will try to fill in a few details about why neutrons are essential to creating stable nuclei.
All stable isotopes excepting Hydrogen-1 have neutrons in their nuclei. ...
- 443
17
votes
Accepted
Hypervalency and the octet rule
Out there in the real world, university students and school pupils alike favour strict rules that are true as often as possible (or at least have clear, easily remembered exceptions), while their ...
- 66k
17
votes
Accepted
What do these labels for molecular electronic states mean?
As stated in this answer, these are irrep (irreducible representation) labels for molecular symmetry point groups. In the context of chemistry, point groups are usually introduced when learning about ...
- 7,347
17
votes
Accepted
Help understanding how "steric effects" are distinct from "electronic effects"?
The normal distinction between "steric" and "electronic" is based on whether the effect is transmitted through space or through bonds
All the normal physical interactions we ...
- 34.3k
16
votes
Can an atom bond with more than 8 other atoms?
There has been quite some interesting work by my former co-worker and my supervisor on metal-rich molecule with the co-ordination higher than eight.
For more see Timo Bollermann, Thomas Cadenbach, ...
- 43.3k
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 ...
- 6,558
15
votes
Accepted
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 ...
- 4,629
14
votes
Can an atom bond with more than 8 other atoms?
In october 2015, 5 months after all the current answers were given, a new cluster compound witn C.N. 16, $\ce{CoB16-}$, has been reported [1]:
Here we report the observation of a large metal-doped ...
- 36.9k
13
votes
Accepted
What is the difference between the KLMN and SPDF methods of finding electronic configuration?
The KLMN(OP) method is based on electron shells, with the labels KLMN(OP) being derived from an experiment in which the spectroscopist wanted to leave room for lower energy transitions in case there ...
- 42.1k
13
votes
Why do atoms need 8 electrons to stabilize?
The valence orbitals of atoms are composed of suborbitals (s and p) there is 1 s suborbital which is spherical and can hold 2 electrons (one with up spin and one with down spin). There are 3 p ...
- 12.1k
12
votes
Why do no known atoms have electrons in the g or h subshells?
Well, the first available sub-shell for "g" electrons would be 5g (i.e., 1s, 2p, 3d, 4f, so 5g). Based on current trends, we'd need row 8 of the periodic table. We just haven't found those elements ...
- 27.5k
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 ...
- 28.2k
12
votes
Accepted
"NBO diagrams" versus MO diagrams
A molecular orbital diagram is a schematic representation of how we interpret bonding in certain species. It is as much an accurate representation for a specific bonding situation as a Lewis structure ...
- 43.3k
11
votes
Why do no known atoms have electrons in the g or h subshells?
According to Umemoto and Saito,[1] starting with element 126, elements would possess $\mathrm{5g}$ electrons. The calculated ground-state electronic configurations for elements 126–131 are:
element ...
- 39.7k
11
votes
Accepted
A unique demo for singlet oxygen?
Admittedly, I'm having a professional photochemical bias when it comes to the generation of singlet oxygen!
A rather safe and simple approach - even in home experiments - is the use of air, sunlight ...
- 43.6k
11
votes
Why does Boron only need 6 valence electrons unlike the standard 8?
The principle of full octet is that most reactivity patterns are described well if there is a driving force / energetic gain for full octets in main-group atoms.
However, the only facet of an atom ...
- 6,558
11
votes
Accepted
Effects of atmospheric gases on colour of aurora
There is good information at Glowing Gases - Aurorae
There are many factors that need to be considered.
Once an atom or molecule is excited, it can lose the energy by collision or by emission of ...
- 39.7k
11
votes
Accepted
Why do rare earth metal oxides vary in color so much?
TL;DR f-f transitions in lanthanide ions give rise to the colours of the ions. The electronic states can be derived from quantum mechanics, and their energies vary from ion to ion, which give rise to ...
- 69.6k
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