Why covalent compounds exist as solid liquid and gaseous states?

Answer 1

Many covalent compounds are what chemists describe as volatile substances, which are relatively easy to either melt or boil. Covalent bonds are not as strong as ionic bonds, so with ionic bonds, you get compounds that are very hard to melt and even harder to boil, so we therefore know them mostly as solids (or as solutes). We do melt sand to make glass, but it takes an extremely high temperature. The other large bonding category is the metallic bond. These can be quite strong and can also result in very high melting points, but they vary. We also get the element Mercury, which has a metallic bond but which is liquid at room temperature.

Answer 2

Covalent compounds can exist in different states (solid, liquid, gas) depending on the strength of the intermolecular forces between the molecules. In solid state, the molecules are packed closely together with strong intermolecular forces holding them in place. In liquid state, the intermolecular forces are weaker allowing the molecules to move past each other. In gaseous state, the intermolecular forces are very weak, allowing the molecules to move freely and independently.