In the [[1]] reaction the nucleophile gets attached either to the positively charged molecules or atoms of the other substance. 

An electron-rich species which can donate its electrons to electron-deficient species is known as a nucleophile. Water, ammonia, and cyanide ion are nucleophiles. In a nucleophilic substitution reaction, a nucleophile gets attached to the positively charged atom or molecules of another substance. In other words, one nucleophile replaces the other in a nucleophilic substitution reaction.