Naked Science Forum

Non Life Sciences => Chemistry => Topic started by: 113zami on 15/06/2008 21:34:45

Title: What determines whether a molecule is more likely to form dimers?
Post by: 113zami on 15/06/2008 21:34:45

this question has confused me for a long time, please help

4)which molecule is likely to form dimers?

a)BF3
b)NO2-
c)NO2
d)NO2+

the correct answer is  C   , C is a radicle and I can uderstand why it would form dimers but why wouldn't the other choices be able to form dimers?, to my knowledge any 2 molecules can form dimers there isn't really a restriction to forming dimers

thanks

Title: Re: What determines whether a molecule is more likely to form dimers?
Post by: Bored chemist on 16/06/2008 21:10:02

Well, 2 of them are charged and if you tried to stick pairs of them together the charges would repel.
BF3 may well form a dimer at very low temperatoures and pressures (as do some of the inert gases) so you have a valid point. However, putting that answer in an exam mihght not help you much.

BF3 is a much more interesting question- BH3 certainly does form a dimer.
I presume it's because the electron withdrawing nature of the fluorines means that there's not much electron density on the boron to do any bonding. That is certainly why it's a strong lewis acid
http://en.wikipedia.org/wiki/Lewis_acid

Anyway, well done for asking an interesting question.

Title: Re: What determines whether a molecule is more likely to form dimers?
Post by: 113zami on 19/06/2008 17:25:20

thank you very much