Question

Why are ionic compounds are formed when a metal from the left side of the periodic table reacts with a nonmetal from the right side, but covalent bonds are formed between nonmetallic elements on the right side of the table?

Answer 1

Ionic bonds are formed  between metals and non-metals.  Metals are on the left side of the Periodic Table.Metals tend to give electrons to attain Noble Gas configuration.  Non-metals are present on right side of the Periodic Table. Non-metals tend  to accept electrons to attain Noble Gas configurations. Metals tend to lose electrons and non-metals tend to gain electrons, so in reactions involving them, there is electron transfer resulting in ionic bond where as

Covalent bonding takes place between non-metals. There is no transfer of electrons, but sharing of valence electrons. this is due to high ionization energies of non metals ,meaning  relatively difficult to remove their valence electrons. So, they share valence electrons with other non-metals.