Polyatomic elements are those that require two or more
atoms bonded into a
molecule to exist naturally.
The polyatomic elements we currently know of are:
Astatine
At2
Bromine
Br2
Chlorine
Cl2
Fluorine
F2
Hydrogen
H2
Iodine
I2
Nitrogen
N2
Oxygen
O2/O3
(O3 is ozone)
Phosphorus
P4
Sulphur
S8
Note: The ones listed with a subscript of 2 are technically diatomic (or biatomic) elements, but I decided to include them here anyway.