To draw a Lewis structure for a covalent compound, begin by
calculating A, the available
electrons, and N, the needed
electrons.
What is A for silicon
tetrachloride, SiCl4?

A = 32

Explanation:

We are given that A is the number of electrons available and N is the needed electrons. These " available electrons " would act as the valence electrons, provided they are the only available electrons to participate in this chemical bonding.

Take a look at the placement of Silicon in the periodic table. It is positioned so that it has 4 valence electrons. Respectively Chlorine is positioned to have 7 valence electrons. There are 4 Chlorine, so determine the available electrons take a look at the math below;