Formula: one or two
letter symbol with a numerical subscript (1 being understood) that represents a single unit of
the fundamental particle (one atom
or one molecule or a formula unit) that makes up the substance.
Two variety of
elements:
Monatomic: The formula is the same as the symbol, eg. He, Ar, Na.
–The formula shows that
the elementary particles are atomic.
Diatomic: Formula contains the subscript 2, eg. H2, O2, N2.
–Elementary particles
are molecules—diatomic molecules.
–Molecules are
particles that are made up of two or more atoms combined (bonded) together.
–Only the following
elements in the periodic table are diatomic elements: Hydrogen, Nitrogen, Oxygen, Fluorine, Chlorine, Bromine and
Iodine.
–The rest are
monatomic.