How many pairs of electrons are shared by the carbon atom with each chlorine atom in the formation of carbon tetrachloride?
Carbon tetrachloride has the formula CCl4. Carbon is the central atom. It shares one pair of electron with each of the four chlorine atoms, forming four single bonds. This completes the octet for carbon (the octet rule states that each atom in a molecule will have eight valence electrons, including shared pairs of bonding electrons and lone pairs.) Each chlorine atom has three unshared or lone pairs of electrons in addition to the pair shared with carbon in a single bond.
Lewis dot structures provide a good way to visualize valence electrons in a molecule. The image below shows the Lewis dot structure for CCl4. There is a total of 32 valence electrons (4 for carbon, 4x7=28 for the four chlorine atoms). The atoms are arranged with the least electronegative in the center (it also usually happens to be the one that's different) and the other atoms added in such a way that each atom has eight electrons (except for hydrogen, which only has two) and the molecule is as symmetrical as possible. There are enough electrons in this structure for four bonds and three lone pairs on each chlorine. When there are not enough electrons to complete atoms' octets, double or triple bonds are used. This is when two or three pairs of electrons are shared between two electrons, respectively.