Matter consists of atoms and molecules. Atoms are the smallest units of matter that retain the physical and chemical properties of individual elements. Molecules, however, consist of two or more atoms chemically bonded together. Molecules generally display characteristics that are distinct from their constituent atoms. For instance, water, a compound whose molecules consist of two hydrogen atoms bonded to one oxygen atom, has drastically different physical and chemical properties than either hydrogen or oxygen alone. A molecule, then, is the smallest unit of a compound that retains the properties of the compound.

Ionic bonds are bonds between ions that attracted to each other because of their opposite electrical charges. The electron imbalance in ions can create negative or positive (e.g., an excess of electrons over protons creates a negative ion). Opposite ions attract one another by electrical force to create an...