How many lone pairs of electrons are in CCl4?

There are three lone pairs of electrons around each chlorine atom that makes up CCl4. The subscript to the right of the elemental symbol for chlorine (Cl) in CCl4 indicates that there are four chlorine atoms in the compound. Therefore, there are twelve (12= 3 x 4) lone pairs of electrons in CCl4.

Lone pairs of electrons are not involved in a chemical bond. In a Lewis dot diagram, these electrons are depicted as dots. Pairs of electrons that are involved in a chemical bond are referred to as shared pairs of electrons.  In Lewis dot diagrams, shared pairs of electrons are depicted as slashes or lines.

In CCl4, a single covalent bond attaches each of the four chlorine atoms to a single central carbon atom. Covalent bonds are created between two nonmetals in order to fulfill what is called the octet rule. The octet rule states that most main-group elements want eight valence electrons in order to be stable. Valence electrons are the electrons that are found in the outermost orbital of an element. Each chlorine is a halogen and contains seven valence electrons. Thus, each chlorine atom wants one more electron in order to fulfill the octet rule. Each carbon atom has four valence electrons. So a carbon atom needs four more electrons in order to fulfill the octet rule.

Shared pairs of electrons are counted toward the number of valence electrons obtained by each atom involved in a covalent bond. Thus, each chlorine obtains an additional electron to fulfill the octet rule when it forms a covalent bond with a carbon atom. Likewise, by sharing one electron from each of the four chlorine atoms in CCl4, the central carbon is also able to fulfill the octet rule.