1. F321 Atoms, Bonds and Groups
The mole concept

2. How is the module divided up?
Teacher 1
Teacher 2
Module 1: Atoms and Reactions
1.1.1 Atoms
1.1.2 Moles and equations
1.1.3 Acids
1.1.4 Redox
Module 2: Electrons, Bonding and Structure
1.2.1 Electron structure
1.2.2 Bonding and structure
Module 3: The Periodic Table
1.3.1 Periodicity
1.3.2 Group 2
1.3.3 Group 7

3. Objectives
Outcomes
To define a range of terms relating to quantitative chemistry
Give definitions of:
A mole
Relative atomic mass
Relative isotopic mass
Relative molecular mass
Relative formula mass
Molar mass

4. Why is the mole so important?
The amount of substance that contains a fixed number of particles.
The number of particles is the same as the number of atoms in 12.0g of the isotope carbon-12.
The number is 6.02 x 1023 mol-1– the Avogadro constant (NA)
Why is the mole so important?

5. Why is the mole so important?
In quantitative chemistry we need to know the amount of particles which react:
A molecule of CO2 does NOT contain 2 times the mass of carbon atoms than oxygen atoms
A molecule of CO2 DOES contain one carbon atom and 2 oxygen atoms

6. Why is the mole so important?
Atoms are very small
When carrying out practical experiments we are therefore dealing with very large numbers of atoms
The number of particles in a mole is roughly the same as the number of marshmallows needed to cover the land area of North America to a depth of 1 mile.

7. Different types of particles
When a mole of substance is referred to, the type of particles must be specified:
1 mole of oxygen atoms = 6x1023 atoms
1 mole of oxygen molecules = 2x 6x1023 atoms

8. Mass
The relative atomic mass, Ar, of an element is the mass of an atom of the element relative to the mass of carbon-12

9. Mass
The relative isotopic mass, is the mass of an atom of an isotope of an element relative to the mass of carbon-12
Particle
Charge
Relative Mass
Protons +1 1
Neutrons
Electrons -1
0.0005
For example chlorine can exist with 18 or 20 neutrons (always 17 protons)
As chlorine occurs naturally as chlorine-35 and chlorine-37, the relative atomic mass takes account of the natural abundance of each of these isotopes
Relative atomic mass = (75.5 x x 37) = 35.5
100

10. Calculating relative atomic mass
Naturally occurring neon is 90.9% neon-20, 0.3% neon-21 and 8.8% neon-22. Use these figures to calculate the relative atomic mass of naturally occurring neon

11. Relative molecular mass
The relative molecular mass, Mr, of a molecule is the mass of a molecule relative to the mass of an atom of carbon-12.
To calculate Mr, add up the Ar of all atoms in the molecule eg Mr (CO2) = = 44
The relative formula mass is used in place of relative molecular mass where compounds contain ions
Mr (MgCl2) = = 95

12. Molar mass ‘Molar’ means per mole
Molar mass is therefore the mass per mole of substance (units gmol-1)
Molar mass of an element is numerically equal to the Ar for that element
Molar mass of a compound is numerically equal to the Mr for that compound

13. Plenary Can you: Explain the significance of Avogadro’s constant?
Give definitions of:
A mole
Relative atomic mass
Relative isotopic mass
Relative molecular mass
Relative formula mass
Molar mass