Answer marked wrong on my chem quiz?

[Ryan]

I just got my quiz back for chemistry today and I don't understand why I got one of the answers wrong. The question is: The similar chemical behavior of the elements in a given group in the periodic table is best accounted for by the fact that these elements have:
A) the same number of electrons
B) The same number of electrons in the valence shell
C) similar nuclear structures
D) the same number of protons
E) the same number of isotopes.

I put C. She wouldn't explain to me why it was wrong so can someone help?
(no this isn't homework I already did the quiz so don't give me crap about it )

 

[Tristan009]

I believe it's B) the same number of electrons in the valence shell.

I'm sure you know that electrons are structured in shells around the nucleus - the first shells have capacities of 2-8-8 and so on and so on.

The outer shell needs to be filled, so elements with 7 electrons in their third shell (also the same group) will all react with the need to take one more electron in.

Elements are sorted into groups by the number of electrons in the valence shell.

 

[cathrl69]

It's B. Chemical behaviour is pretty much entirely determined by electron structure - the nucleus is so tiny that it isn't involved (when it is involved, you're studying particle physics reactions). Going down, for instance, the first group, they all have one electron in the valence shell.

I'm assuming you were told which group it was - for some groups it's determined by similar numbers of _gaps_ in the valence shell (i.e. the one before the noble gases, where every element has one gap).