WRITING FORMULAS
General rules:
1. When non-metals bond to form a compound, molecules are formed. The atoms in
the molecule share electrons (electrons overlap). COVALENT BONDING.
2. When a metal bonds with a non-metal, electron(s) aretransferredfrom the metal to
the non-metal to form a positive ion (cation) and a negative ion (anion). These ions
attract each other. IONIC BONDING.
Learn the formulas for the following very common molecules:
Ammonia NH3 (Don’t confuse with ammonium ion NH44+)
Carbon monoxide CO
Carbon tetrachloride CCl4
Carbonic acid H2CO3
Hydrochloric acid HCl
Nitric acid HNO3
Phosphoric acid H3PO4
Sulphur dioxide SO2
Sulphuric acid H2 SO4
Sulphurous acid H2SO3
Water H2O
Diatomic Molecules:
There are 7 elements that are MOLECULES in their pure/uncombined state:
Hydrogen H2
Nitrogen N2
Oxygen O2
Fluorine F2
Chlorine Cl2
Bromine Br2
Iodine I2
They are only diatomic when they are pure.