Elements in the middle of the periodic table don’t tend to form ionic bonds, particuarly those in the p block. They tend to share rather than exchange electrons to achieve a full valence shell.

The term valency is the number of electrons an atom can combine with in it’s outer shell. The electronegativity will dictate how close the elctrons sit to an atom in a bond.

Covalent bonds are more common than ionic bonds in living organisms. Examples of covalent bonds include 02, c02, h20, in additions to DNA and protein.