Molecular Formula: Covalent compounds and elements exist as molecules.

• Empirical Formula: It is the simplest whole number ratio of atoms of each element in a compound.

Used for giant structures of metals and ionic.

• Relative Molecular Mass: Mr. Add relative atomic mass of each element making up molecule.

• Relative Formula Mass: Add relative atomic masses of elements in empirical formula.

• Calculating Empirical Formula: May need to do some subtraction/ addition if masses not needed

given.

– Find moles and simplify ratio by dividing by smallest number.

– Multiply if .5 or .7 (multiply by 3). If .2 can multiply by 5. Round up if can round up all of them.

– Write empirical formula in order appeared in question.

• Calculating Molecular Formula:

– Find empirical formula and its Mr.

– Divide the Mr of the molecular formula by Mr of empirical formula.

– Multiply this factor by empirical formula.

• Knowing Compound but Not Element in the Compound:

– Divide Ar of element by Mr of substance to find percentage of element in whole compound.

– Multiply percentage by the mass of the compound to find out mass of the individual element.

– Use Mr Moles to find moles of element.