Question

how can a covalent bond be formed in a compound

Answer 1

Some compounds consist of two atoms which are both electronegative or both electropositive in which case donation and accepting of electrons cannot happen,i.e, electrovalent/ionic bonds cannot be formed. In such cases, a covalent bond is formed. This is a result of sharing of electrons between two or more atoms which are in need of electrons to form a stable octet config. The covalent bond binds two atoms by direct linkages ( shared electron bond pairs )  as opposed to electrostatic attraction forces in ionic compounds. Atleast one electron has to be contributed by each atom of a compound for it to be covalent. All molecules of atoms are formed due to covalent bonding. Covalent bonding can happen by having 1 bond pair( single bond, H2), 2 bond pairs ( double bond, O2), 3 bond pairs ( triple bond, N2).