What are covalent substances?

Covalent substances contain covalent bonds. For example,
H2, HCl and H2O contains covalent bonds. Covalent bonds are formed by sharing a pair of
electrons, inorder to become stable. They are held together by strong electrostatic
forces between the nucleus (which is positively charged) and the electron pair which is
negatively charged. Covalent bonds are often showed by dot and
cross diagrams.