Kaplan Gen Chem Ch1, 1.4, q4. IE: valence electrons

[sc4s2cg]

I am definitely missing something.

Determine how many valence electrons come from each subshell in the following atoms:

P in PO4^3-

O in PO4^3-

I took this to mean that the question is asking how many v.e. are being contributed by O and P. So O has 6 valence electrons (it is in group 6), and 6*4 is 24. A total of 24 valence electrons. Similar method for P would give 5v.e. How does Kaplan get 10 for P and 8 for O?

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[shefv]

I think they are asking for the total number of electrons for each of the atoms once they are in the structure

So if you draw out the structure, you have 5 bonds on P which means 10 electrons (5 are coming from P and 5 are covalently shared from O)
and for O, each oxygen has the 8 electrons in total when it is part of this structure

 

[ElectricNoogie]

I agree the Q is a bit confusing as worded but if they are sticking with the correct answer (which makes no mention of subshells??), drawing the Lewis structure on questions like these can make them easier to solve correctly. Here we can see there are 10 total valence electrons around P and 8 total valence electrons around each Oxygen.

 

[Silvija10]

The answer says there are 2 s-electrons, 6 p-electrons, and 2 d-electrons. I understand how you get 10 valence electrons total, but can someone please explain where the 2 d electrons come from for the P in PO_4 (3-)?

 

[Don't Get Psyched]

This is how I thought about it.

Fact: All elements in period three and below on the periodic table can accept electrons into their d subshell.

Process:

The electron configuration (shorthand) for P is [Ne] 3s2 3p3 so you get 5 valence electrons from P. The oxygens also contribute 5 valence electrons through bonding. This gives us a total of 10 electrons.

We know that the s subshell can only hold 2 electrons and the p subshell can only hold 6 electrons. This will account for 8 out of the 10 electrons. However, now the s and p subshells are full. The final 2 electrons are held in P's d subshell (which is normally empty for elemental phosphorus).

A similar thing actually happens when analyzing the sulfur in a sulfate ion. 4 electrons end up entering the sulfur's d subshell.

 

[Koalakhoa]

@Don't Get Psyched: How would you know that oxygen will contribute 5 valence electrons through bonding without drawing a Lewis structure, or is that your reasoning after seeing there are 5 bonds to P (thus, 10 electrons in total for P)? I just wanted to know if I am missing something in your logic. Many thanks!