F321 Atoms, Bonds and Groups The mole concept

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

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

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?

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

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.

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

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

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 35 + 24.5 x 37) = 35.5 100

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

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) = 12 + 16 + 16 = 44 The relative formula mass is used in place of relative molecular mass where compounds contain ions Mr (MgCl2) = 24 + 35.5 + 35.5 = 95

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

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