Question

Consider the formal charges on $N$ and $B$ in $H_{3}N-B{F}_3$ and indicate which of the following is true?

• A. $N$ is +ve and $B$ is -ve
• B. $N$ is -ve and $B$ is +ve
• C. both $N$ and $B$ carry similar +ve or -ve charges
• D. charge discrimination is difficult to make

Answer 1

The correct option is A $N$ is +ve and $B$ is -ve

Formal charge on $N=$ Number of valence electrons - non-bonding electrons $-\frac{1}{2}\times$ bonding electrons $=5-0-\frac{1}{2}\times 8=+1$

Formal charge on B $=3-0-1\times 8=-1$

Thus $N$ is +ve and $B$ is -ve.