Molecules:
Molecules are groups or clusters of atoms held together through means of chemical bonding. There are two categories of molecule; molecules of a compound and molecules of an element.
Molecules of an Element
In some cases, two single atoms of an element could be attracted to one another through a bond to form a molecule. Instance of this are oxygen, hydrogen, and bromine. Molecular formulas for these are H2, O2, and B2r. Many gaseous elements exist as molecules of two atoms.