Question

The four bonds of carbon tetrachloride (CCl4) are polar, but the molecule is nonpolar because the bond polarity is canceled by the symmetric tetrahedral shape. When other atoms substitute for some of the Cl atoms, the symmetry is broken and the molecule becomes polar. Use Figure 9.20 to rank the following molecules from the least polar to the most polar: CH2Br2, CF2Cl2, CH2F2, CH2Cl2, CBr4, CF2Br2. (Type your answer using the format NH4 for NH4.)

Answer 1

CBr4 < CF2Cl2 <CF2Br2 < CH2Br2 < CH2Cl2< CH2F2

(6)           (5)           (4)           (3)           (2)            (1)

All the molecules are in tetrahedral geometry. The electronegativity series for the elements that we have is, F > Cl > Br > C > H

So, all C - X bonds where X is F, Cl, Br have a partial negative charge on X and positive charge on C, while C - H bond has the opposite polarity.

Based on these collective effect we get the above series.