Q10.75CP - Chemistry: Molecular Nature Of Matter And Change

Question

The four bonds of carbon tetrachloride ( ${\mathbf{CCl}}_4$ ) are polar, but the molecule is non-polar 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 (p. 364) to rank the following molecules from the least polar to the most polar: ${\mathbf{CH}}_2{\mathbf{Br}}_2$ ,  ${\mathbf{CF}}_2{\mathbf{Cl}}_2$ , ${\mathbf{CH}}_2{\mathbf{F}}_2$ , ${\mathbf{CH}}_2{\mathbf{Cl}}_2$ , ${\mathbf{CBr}}_4$ ,  ${\mathbf{CF}}_2{\mathbf{Br}}_2$

Step-by-Step Solution

Answer

The order of polarity is  ${\mathbf{CBr}}_4\mathbf{<}{\mathbf{CH}}_2{\mathbf{Br}}_2\mathbf{<}{\mathbf{CH}}_2{\mathbf{Cl}}_2\mathbf{<}{\mathbf{CH}}_2{\mathbf{F}}_2\mathbf{<}{\mathbf{CF}}_2{\mathbf{Br}}_2\mathbf{<}{\mathbf{CF}}_2{\mathbf{Cl}}_2$

Step 1: Definition

The formation of a polar molecule occurs most frequently when one end of the molecule is said to have more positive charges than the other end, forming an electric pole.

 

Step 2: Structures

The order of electronegativity in fluorine, chlorine, and bromine is F > Cl > Br. Among these molecules ${\mathbf{CF}}_2{\mathbf{Cl}}_2$  is the most polar.

Step 3: Polarity

A molecule becomes nonpolar if it has a symmetric arrangement of groups around it. So ${\mathbf{CBr}}_4$ has no polarity and is nonpolar. 

The electronegativity of bromine is lower than chlorine so${\mathbf{CF}}_2{\mathbf{Br}}_2$  has lower polarity than  ${\mathbf{CH}}_2{\mathbf{Cl}}_2$ Similarly, electronegativity of fluorine is greatest than chlorine and bromine, thus ${\mathbf{CH}}_2{\mathbf{F}}_2$  has a greater polarity than both ${\mathbf{CF}}_2{\mathbf{Br}}_2$  and ${\mathbf{CH}}_2{\mathbf{Cl}}_2$  .

Similarly due to electronegativity of fluorine> chlorine> bromine, the order of polarity is  ${\mathbf{CF}}_2{\mathbf{Br}}_2\mathbf{<}{\mathbf{CF}}_2{\mathbf{Cl}}_2$