This question regarding quantum number

• TT0
The question is badly posed - I wouldn't waste my time on it. If someone insists, I would say the correct answer is B, as this is the only one that fits the given substitution scheme.In summary, the correct set of quantum numbers for the eighth electron that fills the orbitals in an atom of oxygen is B (n = 2, l = 1, ml = +1, ms = -1/2). The question is poorly phrased and may be trying to target Hund's rules, but in this case, there is no specific order for placing the electrons in degenerate orbitals. So, while A may also be a possible answer, B is the only one that fits the given substitution scheme.

TT0

What is the correct set of quantum numbers for the eighth electron that fills the orbitals in an atom of oxygen?

A. n = 2, l = 1, ml = –1, ms = –1/2
B. n = 2, l = 1, ml = +1, ms = –1/2
C. n = 2, l = 1, ml = +1, ms = +1/2
D. n = 2, l = 0, ml = –1, ms = +1/2
E. n = 1, l = 1, ml = +1, ms = –1/2

I chose B, because it is in the 2nd shell, p subshell, on the right orbital and has a negative spin. But they said the answer is A. This website sometimes has errors so could someone tell me if I am right?

Personally, I don't quite like the way the question is phrased - how does one define "the eighth electron in an atom of oxygen"? It only makes sense if you make reference to the ground state of the +1 oxygen ion.

The answer by the site seems correct to me. Have you heard of Hund's rules?

TT0
I see, I realized I was thinking about the eighth electron on the 2nd shell and not overall, thanks!

TT0 said:
I see, I realized I was thinking about the eighth electron on the 2nd shell and not overall, thanks!
My bad - I was actually the one thinking about the eighth electron on the second shell!
So in that case, your answer is correct, and the site is wrong, because Hund's second rule is to maximise L, and so the 4th electron in the 2p shell should be in the ml = +1 orbital.

TT0
Does ml value really matter? I can be wrong, but these are degenerate orbitals (with the same energy), so the electron doesn't care what is the ml value. When there is an external magnetic field, it can make things different, but in an isolated atom question doesn't make much sense to me.

TT0
Borek said:
Does ml value really matter? I can be wrong, but these are degenerate orbitals (with the same energy), so the electron doesn't care what is the ml value. When there is an external magnetic field, it can make things different, but in an isolated atom question doesn't make much sense to me.
Indeed, the question doesn't make any sense.

TT0 and Borek
Yes, taken on its own, the question doesn't make much sense. I strongly suspect the question is trying (in some way) to specifically target Hund's rules. Using Hund's rules, one would systematically "place" the electrons one-by-one to determine the J and S values for the atom. So, the "eighth electron" technically refers to the "last" electron to be "placed" in this scheme.

TT0
Fightfish said:
Using Hund's rules, one would systematically "place" the electrons one-by-one
That's the Aufbau principle.

Fightfish said:
So, the "eighth electron" technically refers to the "last" electron to be "placed" in this scheme.
Yes, but as Borek said, the ##m_l## and ##m_s## states being of equal energy, there is no "order" in which to put in the electron.

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Somehow I suspect someone was confusing a convention (when drawing orbitals we always fill squares from the left) with the "real" thing, assumed this order matters and extended the idea to ml values. Pure speculation on my side, but I have seen similar thinking on several occasions

So is A still the correct answer?

TT0 said:
So is A still the correct answer?
As far as I am concerned, there is no correct answer, but it can't be D.

What is a quantum number?

A quantum number is a numerical value that describes the energy state of an electron in an atom. It helps to define the electron's position, energy level, and spin.

How many quantum numbers are there in an atom?

There are four quantum numbers in an atom: the principal quantum number, the azimuthal quantum number, the magnetic quantum number, and the spin quantum number.

What does the principal quantum number represent?

The principal quantum number, also known as the n value, represents the energy level of an electron. It can have any positive integer value starting from 1.

What is the significance of the azimuthal quantum number?

The azimuthal quantum number, also known as the l value, represents the shape of the electron's orbital. It can have values from 0 to n-1, where n is the principal quantum number.

How do quantum numbers affect an atom's properties?

Quantum numbers determine the energy, location, and orientation of an electron in an atom, which in turn affects the atom's properties such as size, shape, and reactivity.