SQA National 5 Chemistry Area 1 Chemical Changes and Structure: a complete overview of rates, atoms, bonding, the mole and acids

Area 1, Chemical Changes and Structure, is the quantitative and structural core of SQA National 5 Chemistry. It runs from the atom upwards: what atoms are made of, how they bond, how to count them with the mole, how fast they react, and what happens in acid-base chemistry. This guide pulls the five key areas together; each has its own key-area page with worked questions.

Rates of reaction

A reaction can only happen when reacting particles collide. Anything that makes successful collisions more frequent speeds the reaction:

• Concentration: more particles in a given volume means more frequent collisions.
• Particle size: smaller pieces of a solid give a larger surface area, so more collisions happen at the surface.
• Temperature: warmer particles move faster, collide more often, and a greater proportion of collisions have enough energy to react.
• Catalyst: speeds the reaction by providing an easier pathway, and is not used up.

You measure rate by following a quantity over time, such as the volume of gas, the loss of mass or a change in colour. A rate graph is steepest at the start and levels off as reactants run out. The average rate is the change in quantity divided by the time taken, and you must always give the unit.

Atomic structure

An atom has a nucleus of protons (charge $+1$, mass 1) and neutrons (charge 0, mass 1), with electrons (charge $-1$, almost no mass) in energy levels around it. The atomic number is the number of protons, the mass number is protons plus neutrons, and a neutral atom has equal protons and electrons. Electron arrangements such as $2, 8, 1$ for sodium control how an element reacts.

Isotopes are atoms of the same element with the same atomic number but different mass numbers, because they have different numbers of neutrons. The relative atomic mass is the average mass of the atoms, weighted by how common each isotope is, which is why it is often not a whole number.

Bonding and properties

A covalent bond is a shared pair of electrons between non-metals; an ionic bond is the electrostatic attraction between oppositely charged ions, formed when a metal transfers electrons to a non-metal. Three structures explain properties:

• Covalent molecular: small separate molecules, low melting points, do not conduct.
• Covalent network: one giant structure of atoms, very high melting points, do not conduct (except graphite).
• Ionic: giant lattice of ions, high melting points, conduct only when molten or dissolved.

The exam marks come from linking a property back to the structure, for example explaining why an ionic compound conducts only when molten because the ions are then free to move.

Formulae and reacting quantities

Write formulae by balancing valencies or using the group-ion formulae in the data booklet, and balance equations by placing numbers in front of formulae (never changing a formula) with state symbols. Then comes the quantitative work:

• The mole and gram formula mass with $n = m / \text{GFM}$.
• Concentration with $C = n / V$, the volume in litres.

These are the engine of the whole course, reused in titrations, energy and reacting quantities.

Acids and bases

The pH scale runs below 0 to above 14: acids below 7, alkalis above 7, neutral at 7. Diluting any solution moves its pH towards 7. Non-metal oxides dissolve to form acids; soluble metal oxides and hydroxides form alkalis. Neutralisation of an acid with a base, alkali, oxide, hydroxide or carbonate gives a salt and water (plus carbon dioxide with carbonates), and the salt is named from the metal and the acid. Spectator ions are unchanged on both sides, so every acid-alkali neutralisation reduces to $\text{H}^+ + \text{OH}^- \rightarrow \text{H}_2\text{O}$. A titration finds an unknown concentration using moles and the mole ratio.

How to revise Area 1

1. Learn the definitions and structures precisely, because the marks are in the exact wording.
2. Drill the four calculations (average rate, the mole, concentration, titration) until automatic.
3. Practise mixed questions that join key areas, because the exam often combines a formula, an equation and a mole calculation.
4. Finish with SQA past papers and marking instructions.

For the official course specification, visit sqa.org.uk and always revise from the current specification.