Predict the bond angles about each nitrogen in the dinitramide ion...?

Question

Predict the bond angles about each nitrogen in the dinitramide ion.
NNN
a. 90°
b.107.5°
c.109.5°
d.120°
e.180°
ONN
a.90°
b.107.5°
c.109.5°
d.120°
e.180°
ONO
a.90°
b.107.5°
c.109.5°
d.120°
e.180°

*Thank you! & Could you also please explain how you determined the answer?

Answer 1

First let's draw a diagream of dinitramide:

::O=N=O::
......|
H - N :
......|
::O=N=O::

Now looking at this, we can see that VESPR would put the central N in a tetrahedral arrangement - it has three single bonds and an electron pair. This would normally give a bond angle of 109.5 degrees, but whenever one of the groups is a lone pair, it ends up skewing the angles a bit further (like water and ammonia). So of the choices, (b) 107.5 seems best for NNN.

The side N's each have two Os and an N - a trigonal arrangement. That's 120 degrees, which would be the answer for the NNO and the ONO angles.

Hope that helps!

Answer 2

The answer to all of them is 120. I just did the web assign by guessing with two accounts, that's how I found the answer.

Answer 3

B 107.5