Question

What's the difference between electron geometry and molecular geometry?

Answer 1

You know that electrons pairs assume a geometry .........

Explanation:

You know that electrons pairs assume a geometry that MINIMIZES electrostatic interaction between the pairs. And these geometries correspond to classic Platonic geometries: straight-line; trigonal plane; tetrahedron; trigonal bipyramid; octahedron ....depending on the number of electron pairs, i.e. 2, 3, 4, 5, 6....

But we describe molecular geometry on the basis of bonding electron pairs NOT the number of electron pairs. And the simplest way to appreciate this is to consider the geometries of a common molecules, say water.... We have `2xx1_H + 6_O=8` valence electrons, i.e. 4 electron pairs. And these pairs form a tetrahedron around the central oxygen atom. And the `/_H-O-H` WOULD be `109.5^@` but for the fact that the oxygen lone pairs tend to compress `/_H-O-H`, such that we observe values of `/_H-O-H=104-105^@`.

So both electronic and molecular geometry follows VESPER, but we describe MOLECULAR geometry solely on the basis of bonding pairs between different atoms. The interhalogen molecules are a good example of this.