Diatomic molecules are composed of only two atoms, of either the same or different chemical elements. The bond in a homonuclear diatomic molecule is non-polar due to the electronegativity difference of zero.

When the two bonded atoms are atoms of the same element, the electronegativity difference is 0, and the bond is nonpolar covalent. So the bond character of the O-O bond in hydrogen peroxide, H2O2 , is nonpolar covalent, because the electronegativity difference is 0.

Hydrogen chloride is a diatomic molecule consisting of H atom and Cl atom connected by a covalent single bond. Since the Cl atom is much more electronegative than the hydrogen atom, the covalent bond between two atoms is quite polar.

Some covalently bonded atoms also have lone pairs, that is, pairs of valence electrons that are not involved in bonding. As you look at LiCl, looks to be ionic because of the electrostatic forces of attraction between positive and negative ions.

Because a homonuclear diatomic molecule contains only a single element, the rules that are typically used for naming covalent molecules are not applicable. For example, consider Cl2, the molecule that is formed when two chlorine atoms bond with one another.

Sugar and ethanol are covalent compounds that are soluble in water, because they contain O-H groups that can H-bond to the water. Nonpolar compounds like hydrocarbons have weak intermolecular attractive forces.

Nonpolar compounds do not dissolve in water. The attractive forces that operate between the particles in a nonpolar compound are weak dispersion forces. However, the nonpolar molecules are more attracted to themselves than they are to the polar water molecules.

Although many covalent compounds don’t dissolve in water, some do. Most of the covalent compounds that dissolve in water form solutions that have uncharged molecules. Sugar is a covalent compound that dissolves in water.