Oxygen is represented by a red object. Oxygen forms two bonds. Oxygen can form one double bond or two single bonds. Carbon is represented by a black object. Carbon forms four bonds.
Chlorine is represented by a green object.
Chlorine in organic compounds can form one bond. Life is not as simple in inorganic compounds but chlorine only forms single bonds. Nitrogen is represented by a blue object. Nitrogen forms three bonds. One of the four prongs on a nitrogen is always left open to represent a lone-pair of electrons.