Lesson 2: Ionic and Molecular Compounds

Multivalent Metals: Transition metals show more than one charge. For example, iron shows charges of 3+ and 2+. When it reacts with a nonmetal such as oxygen, it can form two compounds, Fe₂O₃ or FeO
a) Stock System(IUPAC system):
Name the metal followed by the size of the charge on the metal followed by the name of the nonmetal. 

Example:
 Fe₂O₃: iron (III) oxide (red as iron three oxide). 
FeO: Iron (II) oxide. 
b) Classical System: Latin naming system in which the ion with the grater charge receives an -ic ending, the smaller charge has an -ous ending.
Ex Fe₂O₃: ferric oxide
FeO: ferrous oxide
Cu₂O: copper (I) oxide
CoN: cobalt (III) nitride
PtCl₂: platinum (II) chloride

Polyatomic ions stay together in most chemical reactions and are treated in the same way that individual ions are treated when making an ionic compound. Most polyatomic ions are negatively charged but for ammonium. Most names for most of the complexion end in 'ate. 
Example:
 Lithium carbonate:
Li⁺  CO₃^2- = Li₂CO₃

Nickel (II) hydrogen carbonate:
Ni²⁺ HCO₃^- = Ni(HCO₃)₂

Ammonium: NH4
Borate: BO₃^-
Chlorate: ClO₃^-
dihydrogen phosphate: H₂PO₄^- 

Your textbook and data booklet will have the most common polyatomic ions so, no need to memorize them. 

Compounds with endings other than -ate
Many compounds can be formed by adding oxygen or hydrogen or by taking away oxygen. 
Examples:
chlorate- ClO₃^-
perchlorate: ClO₄^-
chlorite: ClO₂^-
hypochlorite: ClO^-

Diatomic Molecules:
All group 17 elements plus oxygen, nitrogen and hydrogen are diatomic. Their formulas as follows:

F₂, Cl₂, Br₂, I₂, At₂, N₂, O₂, H₂
There are two polyatomic molecules; sulfur (S₈) and phosphorus (P₄). 

There are some molecules have become known by common names. 
Example:
ozone: O₃
ammonia: NH₃
glucose: C₆H₁₂O₆