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Questions tagged [electronic-configuration]

In atomic physics and quantum chemistry, the electron configuration is the distribution of electrons of an atom or molecule (or other physical structure) in atomic or molecular orbitals.

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Can an atom have more than 8 valence electrons? If not, why is 8 the limit?

According to some chemistry textbooks, the maximum number of valence electrons for an atom is 8, but the reason for this is not explained. So, can an atom have more than 8 valence electrons? If ...
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Why do elements in columns 6 and 11 assume 'abnormal' electron configurations?

When I look around for why copper and chromium only have one electron in their outermost s orbital and 5/10 in their outermost d orbital, I'm bombarded with the fact that they are more stable with a ...
Gordon Gustafson's user avatar
65 votes
4 answers
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How can one explain niobium’s weird electronic configuration?

As cited in an answer to this question, the ground state electronic configuration of niobium is: $\ce{Nb: [Kr] 5s^1 4d^4}$ Why is that so? What factors stabilize this configuration, compared to ...
F'x's user avatar
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43 votes
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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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42 votes
6 answers
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Can an atom bond with more than 8 other atoms?

Is it possible for an atom to bond with 8 other elements (same or other type)? If yes, then please give some examples. If no, then what could be the possible reason for it? My question is not about ...
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Why is the vanadium(3+) ion paramagnetic?

I know that the electron configuration of vanadium is $[\ce{Ar}]\mathrm{4s^2 3d^3}$. None of the electrons in the 3d subshell are paired. Once it loses these three electrons, shouldn't the remainder ...
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40 votes
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Why is gold unreactive when only one electron is in the outer shell?

I've been trying to answer my (high school) daughter's questions about the periodic table, and the reactivity series, but we keep hitting gaps in my knowledge. So I showed that the noble gases have a ...
Darren Cook's user avatar
36 votes
3 answers
1.2m views

What are the maximum number of electrons in each shell?

In my textbook, it says that the maximum number of electrons that can fit in any given shell is given by 2n². This would mean 2 electrons could fit in the first shell, 8 could fit in the second shell, ...
user3034084's user avatar
36 votes
1 answer
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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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34 votes
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Hypervalency and the octet rule

I realize that the octet rule is more a suggestion than a rule, and that it applies mainly to non-transition metal compounds. Still, compounds that don't have an octet, like $\ce{BH3}$, tend to ...
ron's user avatar
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31 votes
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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 does the 3rd electron shell start filling up with scandium?

The electron configuration of calcium is 2, 8, 8, 2, where up to that point each shell, asides from the first shell counts up to 8 - why then does scandium have an electron configuration of 2, 8, 9, 2?...
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27 votes
2 answers
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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. For $\ce{N2}$ the orbitals in increasing energy ...
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While filling electrons, we follow Aufbau principle, but not while removing them. Why is this so?

I recently came across a question Why is the vanadium(3+) ion paramagnetic?, where the asker is wondering how $\ce{V^{3+}}$ is paramagnetic (he used Aufbau in reverse to remove the electrons), while ...
Pritt says Reinstate Monica's user avatar
25 votes
4 answers
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Why does the energy gap for π - π* transitions shrink with the size of the pi-conjugated system?

Quoting from this site: As conjugated pi systems become larger, the energy gap for a π - π* transition becomes increasingly narrow, and the wavelength of light absorbed correspondingly becomes ...
user4717's user avatar
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23 votes
2 answers
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Which relatively simple molecules violate the octet rule?

I'm learning how to draw Lewis diagrams. Everything I've read emphasizes the octet rule. However, to the best of my knowledge, that rule only applies to elements in the first three periods. On our ...
Hal's user avatar
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22 votes
3 answers
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Are there any major exceptions when comparing electron affinity?

I was tasked with figuring out whether carbon or nitrogen has a more negative electron affinity value. I initially picked nitrogen, just because nitrogen has a higher $Z_\mathrm{eff}$, creating a ...
Zolani13's user avatar
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22 votes
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Is the Springborg 6D phase space model used in modern molecular orbital modeling?

In various papers written in the 1980s, Michael Springborg explored an interpretation of the Wigner phase space function as an electron density in a six-dimensional $(q,p)$ phase space. He applied it ...
Terry Bollinger's user avatar
21 votes
5 answers
298k views

What is SPDF configuration?

Recently in my chemistry classes, the teacher spoke about SPDF configuration and then said that we'll be taught about it in higher classes. But I'm sorta curious to know that what is SPDF ...
Anoneemus's user avatar
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21 votes
6 answers
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Why do atoms need 8 electrons to stabilize? [duplicate]

As the title says. I have surfed all of the net but could never find the answer to this question. Why do atoms need 8 electrons to stabilize? I mean why not 7 or 5 or 10 electrons? Why specifically 8? ...
MartianCactus's user avatar
19 votes
4 answers
5k views

Will adding up protons and electrons (without neutrons) create a new element?

If protons have a positive charge and electrons have a negative charge, can we add up several protons and electrons together to create a new element, without adding neutrons to hold the nuclei ...
soundslikefiziks's user avatar
19 votes
1 answer
21k views

Why can Cu have an oxidation number of +2?

The electronic configuration for $\ce{Cu}$, adjusted for Hund's rule, is: $[\ce{Ar}] 3d^{10} 4s^1$ So, shouldn't $\ce{Cu}$ have an oxidation number of $+1$? whereby it gives off its outermost 4s ...
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Difference between Coupled Cluster and Full CI

I'm looking at some high precision quantum chemistry methods like Coupled Cluster (CC) and FULL CI (FCI). It seems both CC and FCI start from Hartree-Fock and then excite the electron to higher ...
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18 votes
3 answers
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Have there been no advances in the determination of effective nuclear charges since Clementi and Raimondi in the 60s?

Effective nuclear charge is a very important concept in chemistry, and is the basis for the qualitative explanation of many observed chemical and physical properties, including several periodic trends....
Nicolau Saker Neto's user avatar
18 votes
1 answer
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Plutonium having more oxidation states than samarium?

Why does plutonium have more oxidation states than samarium? Electron configuration of Pu: $\ce{[Rn] 5f^6 7s^2}$ Electron configuration of Sm: $\ce{[Xe] 4f^6 6s^2}$ I thought that only the valence ...
user avatar
18 votes
3 answers
70k views

Anomalous electronic configuration of platinum

Why is the electronic configuration of platinum $$\mathrm{[Xe] 4f^{14} 5d^9 6s^1}$$ and not $\mathrm{[Xe] 4f^{14} 5d^{10} 6s^0}$ or $\mathrm{[Xe] 4f^{14} 5d^8 6s^2}$?
lambda23's user avatar
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17 votes
2 answers
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What do these labels for molecular electronic states mean?

What do these symbols mean in excited states? $${}^2\!A_2,{}^2\!B_1,{}^4\!A''$$ I am confused with these representations, found in the abstract of this paper. I think it is kind of a representation ...
Chao Song's user avatar
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16 votes
1 answer
731 views

Why is an energy cost associated with splitting the HOMO spins in singlet oxygen?

The molecular orbital schemes for both forms of singlet oxygen ($\mathrm{^1\Delta_g}$ and $\mathrm{^1\Sigma_g^+}$) and triplet oxygen ($\mathrm{^3\Sigma_g^-}$) are typically given as shown in the ...
Jan's user avatar
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Why is the 2-position of pyridine electron richer than the 4 position

I am wondering about the electronic structure of pyridine. If we look at nucleophilic substitution, which favored on electron poor centers, for 2-chloro and 4-chloro pyridine we see that the ...
DSVA's user avatar
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15 votes
2 answers
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Help understanding how "steric effects" are distinct from "electronic effects"?

@jakebeal's excellent answer to Why do animal cells “mistake” rubidium ions for potassium ions? includes the following passage: In the case of potassium versus sodium, which are both very important ...
uhoh's user avatar
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15 votes
2 answers
330 views

Does exotic potassium exist?

I was reading a book called 'Hundred and Seven Stories of Chemistry'. There is a chapter about how the attributes of different elements can change in presence of enormous pressure and temperature. ...
Mockingbird's user avatar
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15 votes
1 answer
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Why do rare earth metal oxides vary in color so much?

I only know a little about what causes different color, but I know it has to do with the electron orbitals and how they reflect or absorb/emit incoming light. The rare earth metals are in the ...
Ryan's user avatar
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15 votes
1 answer
12k views

Why is the 5d orbital instead of the 4f orbital filled in lanthanum?

For orbitals with the same value of $n + l$ (e.g. the $\mathrm{3d}$ and $\mathrm{4p}$ orbitals), we usually expect the orbital with the lower value of $n$ to be filled earlier. Hence, for example, the ...
Diyanko Bhowmik's user avatar
15 votes
1 answer
246 views

Analysis of post-HF wavefunctions

Hartree-Fock method introduces electron (spin)orbitals and they are commonly used for qualitative rationalization of many molecular properties. However, MOs have meaning only if we ignore electron ...
permeakra's user avatar
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14 votes
1 answer
239 views

Aurora borealis - less favored energy transitions higher in atmosphere?

This question describes how some energy transitions become more prominent as you higher in the atmosphere. Short summary: Some electron transitions are "forbidden" by quantum mechanical selection ...
Adroit's user avatar
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13 votes
3 answers
645 views

What is the usage of orbitals more complex than f orbitals?

Every high school learner, in each corner of the world, faces the lesson History of Atom during his courses, just as I did. We learned about s, p, d and f orbitals, though there were no signs of ...
M.A.R.'s user avatar
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13 votes
3 answers
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Effects of atmospheric gases on colour of aurora

Recently I moved to the north of Norway, so I've seen quite a few auroras. Because the colour is mainly green, I was sure this must be due to electron transitions in $\ce{N2}$ (because the atmosphere ...
Adroit's user avatar
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12 votes
2 answers
803 views

Why are protons more common than hydride ion?

I'm a high school student. I noticed $\ce{H+}$ ion is commonly present in my books while I didn't find any presence of $\ce{H-}$ ions in my books. However, I found on internet that $\ce{H-}$ also ...
Oshawott's user avatar
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12 votes
2 answers
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Why do 3d orbitals have lesser energy than 4s orbitals in transition metals? [duplicate]

This is quoted from Jim Clark's Chemguide For reasons which are too complicated to go into at this level, once you get to scandium, the energy of the 3d orbitals becomes slightly less than that of ...
user avatar
12 votes
1 answer
1k views

"NBO diagrams" versus MO diagrams

Molecular orbital diagrams are well known by chemists. According to Wikipedia (emphasis mine), A molecular orbital diagram, or MO diagram, is a qualitative descriptive tool explaining chemical ...
schneiderfelipe's user avatar
12 votes
3 answers
7k views

Why do iron(II) ions and chromium have different electronic configurations?

What I know: Empty 3d orbitals are higher in energy than empty 4s orbitals Aufbau Principle (electrons always go into an empty orbital with the lowest energy) Partially/half/fully filled 3d ...
lyf's user avatar
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12 votes
2 answers
37k views

Anomalous electronic configurations

Cu has an anomalous electron configuration. $\ce{Cu ~=~ 1s^2~2s^2~2p^6~3s^2~3p^6~4s^1~3d^{10}}$, it does not follow the usual pattern. In this case, the 3d subshell is filled before the 4s, which ...
Cactus BAMF's user avatar
12 votes
2 answers
14k views

Two different electronic configurations for cerium

Depending on the textbook there are two different electronic configurations stated for cerium. On the one hand $$[\ce{Xe}]\mathrm{4f^15d^16s^2}\quad$$ and on the other hand $$[\ce{Xe}]\mathrm{4f^...
Peter Hofer's user avatar
12 votes
1 answer
1k views

Why is the orbital angular momentum of a pi electron along the axis of two atoms' molecule one?

I'm reading quantum chemistry. The book says that the orbital angular momentum of a $\pi$ electron along the symmetry axis of a molecule made up of two atoms is $\pm 1$. I think this is a primary ...
Ben's user avatar
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11 votes
2 answers
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The energy gap between a pi-conjugated system with (2 bonding and 1 anti-bonding orbital) and (1 bonding and 2 anti-bonding) orbitals

I asked a question previously about "why" it is the case the expanding the size of pi-conjugated systems decreases the required energy to excite an electron from a HOMO to a LUMO band: Why does the ...
user4717's user avatar
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11 votes
1 answer
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If the ferric ion is more stable than the ferrous ion, then why is it readily reduced to the latter?

The standard reduction potential value for the ferric ion: \begin{align} \ce{Fe^3+ + e- &<=> Fe^2+} & E^\circ &= \pu{0.77 V} \end{align} The value is positive, hence it means that ...
Avi's user avatar
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11 votes
1 answer
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A Question on the Role of Triplet Oxygen in the Formation of Artemisinin

It is observed that whereas singlet oxygen is required for an ene reaction with an alkene to give an allyic hydroperoxide, triplet oxygen will react similarly with an enol to give an alpha-hydroperoxy ...
iad22agp's user avatar
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10 votes
2 answers
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Degeneracy of second excited state of H-?

This is a question presented in a IIT-JEE 2015 paper I exam. It says, . Not considering the electronic spin, the degeneracy of the second excited state (n = 3) of H atom is 9, while the degeneracy ...
Mockingbird's user avatar
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10 votes
3 answers
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Why might a planar, conjugated molecule be higher in energy than a nonplanar system?

I have a small molecule (23 atoms) for which I want to verify parameters in a molecular mechanics force field. My first step is to look at the potential energy as a function of the dihedral angle, ...
halcyon's user avatar
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10 votes
1 answer
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What are complete active space methods and how are such spaces defined for molecules?

I am new to computational chemistry and would like to know about the active space and inactive space terminologies in MCSCF type calculations. For understanding this I have four systems: $\ce{H2O}$ ...
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