Question

Would you expect the geometry of the ammonium ion to differ from the methane molecule?

Answer 1

Solution
The ammonium ion NH4 + is a regular tetrahedron with nitrogen in the center and with hydrogen atoms at the vertices of the tetrahedron.
The methane molecule is not a tetrahedron, but has a pyramid structure. The distance between two neighboring hydrogen atoms is 1 Å or 10-8 cm, and the height of the pyramid is 0.37 Å.