Why can different numbers of metal and nonmetal atoms create ionic bonds together?

This is because of the ability of some metals and non-metals to form more than one ion.

Explanation: Ionic bond is a type of chemical bond that is formed between non-metallic atom (s) and metallic atom (s) as a result of transfer of electrons. Metallic atom (s) lose electron (s) to form stable ions that are positively charged ions known as cations. On the other hand, non-metallic atom (s) gain the electron (s) lost by the metallic atoms to form a negatively charged ions known as anions. The positively charged ions and the negatively charged ions create an electrostatic attraction which results to the formation an ionic bond. Some metals such as transition elements, copper (Cu) have more than one ions, Cu + and Cu2+. Additionally, non-metals such as nitrogen also forms more than one ions, that is, N3 + and N5+. Therefore, different number of metal and non-metal atoms can create ionic bonds together.