Final answer:
When atoms of different types react, they form a compound, which may consist of ions if electrons are transferred, resulting in ionic compounds. Atoms of one element that differ in the number of neutrons are called isotopes.
Step-by-step explanation:
When atoms of one type react with atoms of other types, a compound is formed. This process often involves the transfer or sharing of electrons among atoms. Atoms within a compound are chemically bonded together in fixed whole-number proportions, and although they can separate and recombine to form new substances, the atoms themselves are neither created nor destroyed during chemical reactions. In some cases, the atoms may gain or lose electrons and form charged particles, or ions, resulting in ionic compounds.
To answer your review question: Atoms that vary in the number of neutrons found in their nuclei are called isotopes.