Amount of substance.

Isotopes: Atoms of the same element with different numbers of neutrons and different masses.

Relative isotopic mass: The mass of an atom of an isotope compared with one-twelfth of an atom of carbon-12.

Relative atomic mass: The mass of an atom of an element compared with one-twelfth of an atom of carbon-12.

Avogadro constant: The number of atoms per mole of a carbon-12.

Molar mass: The mass per mole of a substance.

Empirical formula: The simplest whole number ratio of atoms of each element present in a compound.

Molecular formula: The actual number of atoms of each element in a molecule.

Atom economy: The atom economy of a chemical reaction is a measure of how well atoms have been utilised.

Solids: moles = mass/Mr                                  Mr units are gmol-1

Solution: moles = (C*Vcm3)/1000                  Note: This is all at room temperature and pressure

Gases: moles = V(cm3)/24000                        

Ideal Gas: pV=nRT

p = Pressure (Pa) kPa*1000= Pa

V = Volume (m3)

n = Number of moles

R = Gas constant (8.314 KJmol)

T = Temperature (K)

Empirical formula: The simplest whole number ratio of atoms of each element present in a compound.

1. Find the moles of each element to find the ratio of atoms.

2. Divide each number in the ratio by the smallest of the numbers.

Note: Sometimes percetages are given instead of masses, you can still do it the same way.

Molecular formula: The actual number of atoms of each element in a molecule.

1. Divide the Mr by the empirical formula mass. 

2. Multiply the empirical formula by this number.

The theoretical yield is difficult to acheive for several reasons including;

• The reaction may not have gone to completion.
• Other side reactions may have taken place alongside the main reaction.
• Purification of the product may result in loss of product.

Percentage yield = (actual yield/ theoretical yield)* 100

Atom economy: The measure of how well atoms have been utilised.

Atom economy = (Mr of desired products/ Mr of all products)*100