7+ Year Member
Apr 22, 2009
Dental Student
Im probably overlooking something small but im doing the ADA practise test and #63 and #67 for gen chem is giving me some trouble.

#67: What is the number of unpaired electrons in this atom 1s^2 2s^2 2p^6 3s^2 3p^2.

I thought just the 2in the 3p orbital were not paired :confused: but the answer is 3.

#63. In which two compounds does nitrogen have the same oxidation number?

a) N2O3, HNO3
b) N2O5, HNO3
c) NO2, N2O3
d) N2O4, HNO2
e) HNO2, NH3

the answer is B. (i thought O would be -2x5 = -10, and so n2 would be +10 and in HNO3 H is +1, O -2x3=-6 so N is +5???)

Thanks in advance for the help.


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10+ Year Member
Jan 30, 2009
For the first one, half filled p orbitals are generally more stable than not, so for that configuration, it's actually probably 3s^1, 3p^3. However, when they give you the configuration, that's kind of lame to have you make an assumption for.

For the second one, you forgot to divide your -10 by 2, for n2o5