Classify the following molecules I ions as nucleophiles or electrophiles :
`HS^(-), BF_(3), CH_(3) CH_(2) O^(-), (CH_3)_3 N, CI^(+), CH_3 C^(+) = O, H_(2) N^(-) :, NO_(2)^(+)`

Explanation

(i) Nucleophiles : `Hunderset(..)overset(..)(S):^(-), C_(2)H_(5)underset(..)overset(..)(O):^(-), (CH_(3))_(3)N:, H_(2)overset(..)(N):^(-)`
All these species have one or more lone pairs of electrons which it can easily donate to an electrophile and hence behave as nucleophiles.
(ii) Electrophiles : `BF_(3), Cl^(+), CH_(3)overset(+)(C) = O, overset(+)(N)O_(2)`
All the positively charged species have a sextet of electrons around the positively charged atom and hence can accept a pair of electrons and them behave as electrophiles.
Similarly, B has only a sextet of electrons in the valence shell and hence `BF_(3)`, though neutral, also acts as an electrophile.