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Drawing shapes of molecules

Okay I'll try and word this the best I can. For example, on an exam paper it says the following; " Sodium reacts with ammonia to form the compound NaNH2 which contains the NH2- ion. Draw the shape of the ion...."
Is the negative charge on the ion just one more electron to one hydrogen? Or is it one to each of the hydrogens? I'm not sure.
Help will be very much appreciated :biggrin:

Reply 1

Lizard cream

I think it's that the nitrogen has an extra lone pair of electrons thus has a negative charge. :smile:

The extra electrons would then bend the NH2 group. :smile:

(edited 11 years ago)

Reply 2

Maddie567

Original post by Lizard cream

I think it's that the nitrogen has an extra lone pair of electrons thus has a negative charge. :smile:

The extra electrons would then bend the NH2 group. :smile:

Thank you

Okay, that makes more sense, my heads not in the right place today. So the negative charge now means the the nitrogen has 2 lone pairs and 2 bonded pairs (with the hydrogens)?

Reply 3

Lizard cream

Original post by Maddie567

Thank you

Okay, that makes more sense, my heads not in the right place today. So the negative charge now means the the nitrogen has 2 lone pairs and 2 bonded pairs (with the hydrogens)?

Don't worry we all have one of those days. I was kinda wrong, I was thinking in terms of h20 would have an extra lone pair on the oxygen. As nitrogen is in group below oxygen it would just have an extra electron, not two. So the nitrogen has three electrons on it. Thus bending the molecule. The third electron would normally be used to bond to hydrogen in ammonia. :smile:

hope that helped.

(edited 11 years ago)

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Reply 4

Spoogle

NH2- has the same shape as water, if ever you're unsure what to do with the charge when working out the shape just apply it to the central atom. So in this case the nitrogen gains an electron due to the single negative charge and thus now has 6 in the outer shell and you can see now how it's akin to H2O with a bent shape as you've correctly said, two lone pairs and two bonded pairs.

Reply 5

charco

Study Forum Helper

Original post by Maddie567

Here's a little video that explains it ...

[video="youtube;iNJMyxchdy8"]http://www.youtube.com/watch?v=iNJMyxchdy8&list=PL7D70531B822BC838&index=14[/video]