- Home
- Standard 11
- Chemistry
p-Block Elements - I
medium
The most stable Lewis acid-base adduct among the following is
A$H _{2} O \rightarrow BCl _{3}$
B$H _{2} S \rightarrow BCl _{3}$
C$H _{3} N \rightarrow BCl _{3}$
D$H _{3} P \rightarrow BCl _{3}$
(KVPY-2016)
Solution
(c) A complex formed by the dative bond between Lewis acid and Lewis base is called Lewis acid-base adduct. In all the given cases Lewis acid, i.e. $BCl _{3}$ is same.
So, stability depends on Lewis base.
Among the given options $H _{3} N \rightarrow BCl _{3}$ form stable Lewis base adduct, because $N$ of $NH _{3}$ contains a lone pair and is less electronegative, thus it can donate its lone pair into empty orbital of $BCl _{3}$ (Lewis acid) to form effective dative bond $(p \pi – p \pi)$.
In option $(a),$ $O$ is highly electronegative, so it will not donate its lone pair to $BCl _{3}$.
In option $(b)$ and $(d),$ the formed dative bond $d \pi – p \pi$ is less effective than $p \pi – p \pi$ in case of $NH _{3} \rightarrow BCl _{3}.$
So, stability depends on Lewis base.
Among the given options $H _{3} N \rightarrow BCl _{3}$ form stable Lewis base adduct, because $N$ of $NH _{3}$ contains a lone pair and is less electronegative, thus it can donate its lone pair into empty orbital of $BCl _{3}$ (Lewis acid) to form effective dative bond $(p \pi – p \pi)$.
In option $(a),$ $O$ is highly electronegative, so it will not donate its lone pair to $BCl _{3}$.
In option $(b)$ and $(d),$ the formed dative bond $d \pi – p \pi$ is less effective than $p \pi – p \pi$ in case of $NH _{3} \rightarrow BCl _{3}.$
Standard 11
Chemistry
Similar Questions
Match List$-I$ with List$-II :$
| List$-I$ | List$-II$ |
| $a$ Borax | $i$ $NaBO _2$ |
| $b$ Kernite | $ii$ $Na _2 B _4 O _7 .4 H _2 O$ |
| $c$ Orthoboric acid | $iii$ $H _3 BO _3$ |
| $d$ Borax bead | $iv$ $Na _2 B _4 O _7 .10 H _2 O$ |
