Briefly describe the concept of electronegativity and explain why CCl4 is a non-polar molecule

Electronegativity is the tendency of an atom to attract a pair of electrons in a covalent bond. The Pauling scale assigns values to this tendency for each element in the periodic table ranging from the lowest (Caesium: around 0.7) to the strongest and highest (Flourine at 4.0). Differences in electronegativity between bonded atoms cause these bonds to be polar, the higher the difference the more polar the bond.

In tetrachloromethane (CCl₄) there is a difference in electronegativities of Carbon and Chlorine (0.5). This means the electrons in each bond are not shared equally but pulled closer to the Chlorine due to its higher electronegativity. However the tetrahedral nature of the molecule means that there is equal pull in all directions. All bond polarities cancel out and the molecule has no overal polar effect.