Question #c93e4

1 Answer
anor277
Oct 4, 2016

We use simple #"VSEPR"#, and we use approximation, not calculation.

Explanation:

There are 4 electron pairs around the central nitrogen atom: three are bonding, and one is a non-bonding lone pair.

The geometry around nitrogen is tetrahedral to a 1st approximation. But we describe geometry on the basis of atoms, not on the basis of lone pairs. #/_H-N-H# #~=# #107.5^@#, reduced from the ideal tetrahedral angle of #109.5^@#, due to the influence of the nitrogen centred lone pair. As a non-bonding pair, it is more closely associated with the nitrogen centre, and thus a strong influence on the geometry around nitrogen, acting to compress #/_H-N-H#.

This geometry is precisely analogous to the water molecule, yet here there are TWO oxygen-centred lone pairs, and #/_H-O-H# is compressed to approx. #104.5^@#

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