Why do metals only form ionic compounds while metalloids and nonmetals form ionic and covalent compounds?

According to Fajan`s rules -- nature of bonds formed by larger cations is predominantly ionic since they have less polarizing power. Stronger metal atoms like 1st and 2nd group elements are bigger in size. Hence they are highly electropositive with low ionization potentials and tend to lose electrons easily and thus by forming big sized cations. -- So they are forming Ionic Compounds Whereas, in case of metalloids, the size of cations formed will be small and hence possesses more polarizing power. As a result, they can also form covalent bonds particularly with large anions that can be polarized easily. Non-metals can gain electrons completely to give anions and hence can form ionic bonds. But they can also share electron pairs with other non-metal atoms and can form covalent bonds too. Simply, metals lose electrons and can form only ionic bonds. Metalloids and non-metals not only form covalent bonds by sharing, but can form ionic bonds either by losing or gaining electrons. Thanks & Regards Akshay Meena, askIITians Faculty M.Tech, IIT Kharagpur