Question

Consider the formal charges on $N$ and $B$ in $H_{3}N — BF_{3}$ 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

Answer: (A)

Formal charges on $N$ and $B$ in



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 $B =3-0-\frac{1}{2} \times 8=-1$

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