4. Stoichiometry

-In a symbol equation the number of atoms on each side of the equation should balanced for each element.

-In an equation, remember to write the symbol for the state (aqueous, solid, liquid, gas) in brackets, and the oxidation state of a transition metal in a word equation.

Relative atomic mass, Ar: the average mass of the atoms of an element, relative to the mass of an atom of carbon-12. Relative molecular mass, Mr: the mass of a molecule, found by adding the relative atomic masses of the atoms in it, it is called the relative formula mass for an ionic compound.

Determining the name and formula of a compound:

To determine the formula of an ionic compound the positive charge must equal the negative charge. Naming compounds:

If only two elements are combined, the name ends in ‘–ide’.

Exception: ammonia

With covalent bonds, Greek prefixes are used to denote the number of atoms

1 = mono                                    carbon monoxide

2 = di                            carbon dioxide

3 = tri                            phosphorus trihydride

4 = tetra

5 = penta

6 = hexa

The only time we drop a prefix is if the mono is to appear at the beginning of the name If there is an oxide the ‘a’ or ‘o’ of the prefix is lost e.g. carbon monoxide

If a metal ion is combined with a polyatomic ion in a compound and one is oxygen, the name ends in –ate, except hydroxides

With ionic compounds, the cation (metal) goes first in the name.

With covalent compounds the element further on the left goes first (hydrogen is thought of being in between nitrogen and oxygen so: phosphorus trihydride / hydrogen peroxide)