A covalent substance is a chemical compound in which the atoms are held together by covalent bonds, which are chemical bonds involving the sharing of electron pairs between atoms. Examples of materials that are covalent substances include:

* Hydrogen (H2): Hydrogen gas is a covalent substance composed of two hydrogen atoms bonded together by a covalent bond.

* Water (H2O): Water is a covalent substance composed of two hydrogen atoms and one oxygen atom bonded together by covalent bonds.

* Carbon dioxide (CO2): Carbon dioxide is a covalent substance composed of one carbon atom and two oxygen atoms bonded together by covalent bonds.

* Methane (CH4): Methane is a covalent substance composed of one carbon atom and four hydrogen atoms bonded together by covalent bonds.

* Diamond: Diamond is a covalent substance composed entirely of carbon atoms bonded together by covalent bonds.

* Graphite: Graphite is a covalent substance composed entirely of carbon atoms bonded together by covalent bonds, but with a different arrangement of the atoms than in diamond.

* Quartz: Quartz is a covalent substance composed of silicon and oxygen atoms bonded together by covalent bonds.

* Glass: Glass is a covalent substance composed of various elements, including silicon, oxygen, sodium, calcium, and potassium, bonded together by covalent bonds.

* Plastic: Plastic is a covalent substance composed of various elements, including carbon, hydrogen, oxygen, nitrogen, and chlorine, bonded together by covalent bonds.

These are just a few examples of the many materials that are covalent substances. Covalent substances are found all around us, and they play an important role in our everyday lives.