chem (symbol)

Oxides means the compoounds contaning one oxygen. The general will be XO, X2O... etc, where X is the element with different oxidation state.
For example:
sodium oxide (Na2O)
calcium oxide (CaO)
Notice that for the balanced formula (i.e the comound must be neutral), the cation in this case must be balanced with the oxide ion. Oxide ions have an oxidation state of O2- whereas sodium has an oxidation state of 1+. Therefore, 2 sodium is needed for the complete balancing, resulting in the formula as above. This is the same as CaO, where one Ca is need as Ca is having an oxidation of 2+ .
For dioxide, the general formula will be XO2, examples are carbon dioxide, sulphur dioxide, nitrogen dioxide ...etc. their formula are as follows:
Carbon dioxide (CO2)
Sulphuric dioxide (SO2)
Nitorgen dioxide (NO2)
It was known that the oxidation state for O2 (dioxide) is -4 (as there are 2 x -2 charges), the oxidation state of carbon will be +4 in order to balance the formula to give a neutral molecule.
for ur interest, trioxide will be XO3, pentaoxide will be XO5... etc..
u can refer to the following web site for examples =]
>> http://en.wikipedia.org/wiki/Oxides#Types_of_oxides