Question

When do we use wedges and lines for VSEPR?

Answer 1

When we want to represent a three-dimensional geometry.

Explanation:

It is always difficult to represent a three dimensional object on two dimensional paper. A tetrahedron is a problem, so are trigonal bipyramids and octahedra. Now, when we represent a tetrahedron, say `CH_4`, we can draw 2 `C-H` bonds in the PLANE of the page, and a WEDGE to represent the bond that PROJECTS OUT of the page, and a DASHED LINE to represent the bond that PROJECTS INTO the page.

Note that in order to visualize the geometry, do not embarrassed if you need a model. Such models are always permitted in a test, and would always be found on the desks of distinguished professors of organic and inorganic chemistry.