What elements can on with other elements to form covalent bonds

Non metals join to form covalent bond.

Explanation:

Covalent bond:

It is formed by the sharing of electron pair between bonded atoms.

The atom with larger electronegativity attract the electron pair more towards it self and becomes partial negative while the other atom becomes partial positive.

For example:

In water the electronegativity of oxygen is 3.44 and hydrogen is 2.2. That's why electron pair attracted more towards oxygen, thus oxygen becomes partial negative and hydrogen becomes partial positive.

Both atoms bonded through covalent bond.

In Cl₂ both chlorine atoms are bonded through the covalent bond.