Question

Categorise the following species as electrophiles or nucleophiles: $HS^{-}$, $BF_{3}$, ROH.

Answer 1

Electrophiles are electron deficient.

Nucleophiles are electron rich.

$\sf{HS^-}$ = Nucleophile

$\sf{BF_3}$ = Electrophile

$\sf{ROH}$ = Nucleophile

Answer 2

Electrophiles are those species that are electron deficient and that have strong attraction for electrons. Hence, they are generally positively charged or neutral and they behave as Lewis acid.  

Nucleophiles are those species that are rich in electrons containing a minimum of one lone pair of electrons. As they have tendency to donate electrons, they are generally negatively charged or neutral and they behave as Lewis base .

Thus based on the above definitions, we can categorise as follows:

          $HS^{-}  \rightarrow Nucelophile$ as it is negatively charged .

          $BF_{3}  \rightarrow Electrophile$ as it is a Lewis Acid .

          $ROH \rightarrow Nucelphile$ as it is a Lewis base.