* Empirical and molecular formulas: the purpose of the empirical formula is to find the ratio of any compounds. There are 3 steps to determine the empirical formula:1. Convert mass percent to mass. 2. Convert the mass of each element to moles. 3. Find the mole ratio of the elements. To determine molecular formula from the empirical formula, the molarmass must be obtained from experiment. Example:
% A | g A | X mol A | X mol AY mol B | AxBy |
% B | g B | y mol B | | |
* Describing compound formulas: in terms of thenumber of atoms of each type per molecule or per formula unit --- that is, by giving the formula of the compound. In terms of the mass of each element per mole of compound. In term of themass of each element in the compound relative to the total mass of the compound --- that is, as a mass percent.
* Atoms and molar mass : mass moles conversionMoles to mass Mass to moles
Moles X = gramsGrams X = moles
Molar mass 1/molar mass
*Atomic number and Atomic mass :
Mass number AX atomic number ZX
* Atomic weight: the atomic weight of an element is the averagemass of a representative sample of atoms.
* Formula from mass data : the composition of a compounds in terms of mass percent gives us the mass of each element in a 100.0-g sample.
*Mole : A mole is the amount of a substance that contains as many elementary entities( atoms, molecules, or other particles) as there are atoms in exactly 12 g of the carbon-12 isotope