Aromatic Heterocyclic Compounds

A compound does not have to be a hydrocarbon to be aromatic.
 Many heterocyclic  compounds are aromatic. A heterocyclic compound is a cyclic compound in which
one or more of the ring atoms is an atom other than carbon.
 A ring atom that is not carbon is called a heteroatom. The name comes from the Greek word heteros, which
means “different.” The most common heteroatoms found in heterocyclic compounds
are N, O, and S.
Pyridine is an aromatic heterocyclic compound. Each of the six ring atoms of pyridine
is   sp2  hybridized , which means that each has a p orbital; and the molecule contains three
pairs of electrons.

 Don’t be confused by the lone-pair electrons on the nitrogen; they are not electrons. Because nitrogen is  sp2  hybridized, it has three orbitals and a p orbital. The p orbital is used to form the pi  bond. Two of nitrogen’s of sp2 orbitals overlap the orbitals of adjacent carbon atoms, and nitrogen’s third   sp2  orbital contains the lone pair.

similarly  furan and thiophene are stable aromatic compounds.