Question

Why is CH4 tetrahedral while NF3 is pyramidal?

Answer 1

Here's what I get.

Explanation:

Methane has both tetrahedral electron geometry and molecular geometry.

Methane has four `"sp"^3` orbitals, each pointing towards the corners of a regular tetrahedron with bond angles of 109.5°.

Similarly, ammonia has a tetrahedral electron geometry.

Ammonia has four `"sp"^3` orbitals, each pointing towards the corners of a tetrahedron, with bond angles of 107° ( the bond angles are distorted slightly by the lone pair).

However, our technology can't "see" the lone pair electrons.

All it can detect are the atoms and the angles between them. It "sees" just a trigonal pyramidal arrangement of atoms.

Thus, the molecular geometry of ammonia is trigonal pyramidal.