Question

According to the VSEPR theory, what is the shape of a molecule that has a central atom bound to three other atoms with no lone pairs of electrons?

Answer 1

Trigonal planar.

Explanation:

Three electron pairs surround a central atom, it doesn't matter whether they are bonding or not. VSEPR theory predicts that those electron pairs will be disposed in the geometry that minimizes electron pair repulsion. The result? A trigonal plane with angles of `120""^@` between the electron pairs. Examples include the boron halides, and unsaturated molecules such as ethylene.

Now, dichlorocarbene, `:CX_2` also has 3 electron pairs around the central carbon, and the electron pairs, and the `CX_2` bonds are likewise arranged in a trigonal plane. But we describe molecular geometry on the basis of atoms NOT lone pairs. This dichlorocarbene is predicted to be a bent molecule with `Cl-C-Cl` bond angles `<` `120""^@`.