Empirical and Chemical Formulas

Finding the empirical formula (simplest formula) of a compound

There are 5 basic steps:

1) Start with grams of each element

2) Convert to moles of each element

3) Divide by the smallest number of moles

4) If more than one tenth away from the nearest whole number multiply to make it a whole number

5) Put the elements in the correct order

An unknown compound is made up of 53.54% O and 46.46 % Li

If we had 100 g of this compound, it would contain 53.54 g O and 46.46 g Li.

So...........we can just replace the % with g

Like magic

1) Start with grams

​2) Convert the grams to moles of each element

53.54 g O x 1 mole O = 3.34525 mole O

16.00 g O

46.46 g Li x 1 mole Li = 6.694524 mole Li

6.94 g Li

3) Divide all the moles by the smallest number of moles

53.54 g O x 1 mole O = 3.34525 mole O = 1.00 Oxygen

16.00 g O 3.34525

46.46 g Li x 1 mole Li = 6.694524 mole Li = 2.001 Lithium

6.94 g Li 3.34525

The smallest number of moles is the 3.34525. So divide all the moles by that number

4) If the number of atoms is more than one tenth away from the nearest whole number, multiply by a number to MAKE it a whole number

1.00 Oxygen = 1 O

2.001 Lithium = 2 Li

Our number of atoms is close enough to round to a whole number

-If it contains C, H and other nonmetals it is an organic compound. Put in CHalphabetical order. ( C first, followed by H, followed by any remaining nonmetals in alphabetical order.

- If it is covalent ( and not organic) put in order of lower to higher electronegativity. There are a few exceptions, as always : (

​Covalent or Organic

-The metal goes first and is followed by the anion.

The anion is either a single nonmetal OR a polyatomic ion. You may need to look at your pink sheet

​ Ionic Compound

5) Put the elements in order

​Our compound had a metal, so it is ionic

Li₂O

Open Ended

A compound contains 11.33% C, 45.29 % O and 43.38 % Na. What is the compound?