Which best explains how elements combine in different ways to produce compounds?

There are two kinds that describes how elements combine to form a chemical compound: one is ionic bond  and the other is covalent bond. Ionic bond occurs when metals are combined with nonmetals. The newly formed substance or compound is composed of a positive and negative ions produced by adding/subtracting electrons from neutral atoms and molecules. On the other hand, covalent bond occurs when two nonmetals combine.

They are all full and don't need any more electrons in there outer shell.