Trigonal Bipyramid Bond Angles

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Gloria Quach 1H
Posts: 22
Joined: Fri Sep 25, 2015 3:00 am

Trigonal Bipyramid Bond Angles

Postby Gloria Quach 1H » Wed Oct 28, 2015 12:31 am

Can someone please explain the concept of a trigonal bipyramid having bond angles of 90º and 120º? How would you be able to tell which bond angle applies where in a molecule or would we write both down if asked for bond angle?

Laila Sathe 1D
Posts: 27
Joined: Fri Sep 25, 2015 3:00 am

Re: Trigonal Bipyramid Bond Angles

Postby Laila Sathe 1D » Wed Oct 28, 2015 9:09 am

Think of just one pyramid with a square bottom. The atoms on each corner of the bottom of that pyramid will be 120o away from one another. The atom at the top point of that pyramid will be 90o away from the other atoms because it's in an orthogonal plane. When you add another atom on the opposite side from this "top" atom, you get the trigonal bipyramidal shape. This atom has the same bond angles in relation to the atoms that make up the central triangular plane.

When asked for bond angles, you could say that the bond angles are 90/120o or specify that the atoms in the central triangular plane have a bond angle of 120o and the ones above and below have a bond angle of 90o to that central plane.

This diagram may help:
http://chemistry.elmhurst.edu/vchembook/images2/220pcl5.gif


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