What is the geometry of methane?
Get (or make) a model of a tetrahedron and consider its symmetry.
A tetrahedron has a high-symmetry geometry; in fact, it is one of the Platonic solids. Of course, the methane molecule,
In methane, ALL of the hydrogens can be interchanged by symmetry operations; all of the hydrogen atoms are equivalent because we can use a symmetry operation to interchange each hydrogen with the other. For a start, there is 3-fold symmetry in that each
Chloromethane is less symmetric than methane, but a 3-fold axis of symmetry is retained. Likewise, if I take methane, and replace ANY of the FOUR hydrogens with a heteratom,