Which two atoms form a covalent bond

The atoms which cannot transfer their valance electrons.

Explanation:

A covalent bond is formed between two atoms by sharing of their valence electrons. The shared electrons in a covalent bond are not shared equally between atoms. The atom with higher electronegativity, the electrons will be drawn closer to the nucleus of that atom. This results development of net charge around each nucleus of the atoms in the molecule. Thus, covalent compounds have a small difference in charge are polar. If the atoms in the molecule have the same electronegativity such as in nitrogen (N2), then the shared electrons will not be drawn towards one nucleus more than another, then the bond is non-polar.

consists of mutual sharing of one or more pair of electron between two atoms. These electron are simultaneouly attracted by the two atomic nuclei, A covalent bond forms when the differences between the electronegative of two atom is too small for an electron transfer to occur to form lons.