GChem question - unpaired electrons

[80B]

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first of all, this is my first post on sdn, but ive been reading the forums for months, so id like to give a big thank you to everyone who has contributed, you've been a great help! 😀

i'm studying for dat's right now, scheduled to take them sept 8th. i'm doing pretty well with the info right now, but i ran upon a problem that seems simple, but i can't figure it out...here it is:

(from the ADA DAT sample test 2004, question 67)

"The electron configuration of a particular neutral atom is 1s2 2s2 2p6 3s2 3p2. What is the number of unpaired electrons in this atom?"

The answer key says the answer is 2.

I cannot figure out why it isnt 4. It is silicon right?

Can someone please explain this to me? Thanks alot.

 

[SMC2UCLA2_]

first of all, this is my first post on sdn, but ive been reading the forums for months, so id like to give a big thank you to everyone who has contributed, you've been a great help! 😀

i'm studying for dat's right now, scheduled to take them sept 8th. i'm doing pretty well with the info right now, but i ran upon a problem that seems simple, but i can't figure it out...here it is:

(from the ADA DAT sample test 2004, question 67)

"The electron configuration of a particular neutral atom is 1s2 2s2 2p6 3s2 3p2. What is the number of unpaired electrons in this atom?"

The answer key says the answer is 2.

I cannot figure out why it isnt 4. It is silicon right?

Can someone please explain this to me? Thanks alot.

According to Hund's rule, electrons will occupy empty orbitals before half-filled orbitals. The S subshell of any principle energy level (n) has only 1 orbital with spaces for 2 electrons (paired) while the P subshell has 3 orbitals with space for 2 electrons each. Hund's rule comes into place here- The 2 electrons found in the 3P subshell will both occupy empty orbitals and thus they are unpaired.

You are possibly confusing valence electrons with unpaired electrons. The 2 electrons in the 3S subshell are paired (the have opposite magnetic spins but within the same orbital).

Hope that is clear. Ill be glad to help more.

Good Luck

 

[80B]

i was definitely getting unpaired confused with valence electrons. thanks for your help!