Chemistry - Unit 3: Stoichiometry

what is the molecular formula of a compound?

the number and type of different atoms in one molecule

what is the empirical formula of a compound?

the simplest whole number ratio of the different atoms or ions in a compound

how to deduce the formula of a simple compound from the relative numbers of atoms or ions present in a model or a diagrammatic representation.

count the number of atoms of each element in the model/diagram and repeat for each element

how to deduce the formula of an ionic compound from the charges on the ions

• write out the symbols of each element and write their valencies on top

• to determine the valency of an element, refer to their group number

• swap the valencies of each element and write the number as subscripts (put the number below the element)

• use empirical formula when writing ionic compounds

what are the state symbols used in chemical equations?

• (g) - gas

• (aq) - aqueous

• (l) - liquid

• (s) - solid

how to construct symbol equations with state symbols

1. find the symbols and formulae for each element/compound

2. put into format and see if the number of atoms of each element are the same on either side of the arrow

3. add in state symbols