Question

Which of the following elements is most likely to form a molecular structure that disobeys the octet rule?
1) Ne
2) C
3) O
4) F
5) S

Answer 1

i guessed #1 but the answer is #5, and i dont know why

Answer 2

Hmm it's been a while for me, but for sure Carbon always respects the octet rule (just think of organic chemistry). Neon won't react (well, hardly ever) because it's in the 8th column (noble gases) so its octet is full. Oxygen and Fluorine are quite electro negative in comparison to Sulfur (they are more towards the right in the period table), so it is much more likely that oxygen and fluorine will satisfy the octet rule (they will be more pone to fill their valence shell with electrons to to their electronegativity).

By elemination, sulfur is most likely to not follow the octet rule. In fact, if they ever made you draw molecular structures with sulfur, you often encounter it only having 6 electrons in its valence shell. But I think it had to do with the fact that there was a low energy difference between some of the p orbitals or something which allowed sulfur to do this?? (I'm not sure of this last sentence, but I think recalling that it had to do with sulfur's orbital's energy levels).

Answer 3

will be more prone** to fill their valence shell

Answer 4

due to their electronegativity*
(sorry for all the typos..)

Answer 5

Oh wait I think I got confused in my last explanation. Sulfur won't have just 6 electrons, but actually 6 electron pairs... which would be over the octet rule but still won't obey the octet rule nevertheless. I found something online that somewhat explains the result:
http://chemed.chem.wisc.edu/chempaths/GenChem-Textbook/Exceptions-to-the-Octet-Rule-573.html

(under "Species with expanded octet")

Answer 6

Sometimes just practising drawing molecules will help you find trends/patterns in how the elements will bond to other elements, because it's not always obvious how or why some elements don't follow the octet rule.