Overview
This lecture covers essential topics for AQA GCSE Chemistry Paper 1, including atomic structure, bonding, quantitative chemistry, chemical changes, energy changes, and key practical methods for both higher and foundation tiers.
Atomic Structure and the Periodic Table
- Atoms are the basic building blocks of substances; elements consist of one type of atom.
- Compounds are substances with two or more different atoms chemically bonded.
- Atoms are represented by symbols on the periodic table; atomic number gives proton count.
- Isotopes are atoms of the same element with different numbers of neutrons.
- The mass number equals protons plus neutrons.
- Electron shells fill as 2, 8, 8, 2 (up to calcium, atomic number 20).
- Groups indicate the number of outer shell electrons; periods indicate electron shells.
Types of Substances, Mixtures, and Separation Techniques
- Mixtures contain elements/compounds not chemically bonded (e.g., air).
- Filtration separates insoluble solids; crystallization and distillation separate solutes or liquids by boiling point.
- State symbols: (s) solid, (l) liquid, (g) gas, (aq) dissolved in water.
- Physical changes do not make new substances; only chemical reactions do.
Bonding and Structure
- Metallic bonding: a lattice of positive ions with delocalized electrons; explains conductivity.
- Ionic bonding: metal donates electrons to a non-metal, forming oppositely charged ions.
- Covalent bonding: non-metals share electrons to achieve full outer shells.
- Simple molecular substances have low boiling points due to weak intermolecular forces.
- Giant covalent structures (e.g., diamond, graphite) have high melting points; graphite conducts electricity due to delocalized electrons.
- Alloys are stronger than pure metals due to disrupted lattices.
The Periodic Table, Reactivity, and Groups
- Metals (left of staircase) form positive ions; non-metals (right) form negative ions.
- Group 1 metals (alkali metals) become more reactive down the group.
- Group 7 elements (halogens) become less reactive and have higher boiling points down the group.
- Group 0 (noble gases) are inert due to full outer shells.
Quantitative Chemistry
- Mass is conserved in chemical reactions; equations must be balanced.
- Relative formula mass (Mr) is the sum of atomic masses in a compound.
- The mole relates mass to the number of particles; moles = mass / Mr.
- Limiting reactant is used up first, stopping the reaction.
- Concentration can be given in g/dm³ or mol/dm³.
Chemical Changes and Reactivity
- Reactivity series ranks metals by how easily they lose electrons.
- Displacement reactions occur when a more reactive metal replaces a less reactive metal in a compound.
- Extraction: metals less reactive than carbon can be reduced by it.
- Redox: Oxidation is loss, reduction is gain of electrons ("OIL RIG").
- Acids react with metals and bases to produce salts; neutralization forms water and a salt.
Acids, Alkalis, and Titration (Triple Only)
- pH scale is logarithmic; each pH unit change equals a tenfold change in H⁺ ion concentration.
- Strong acids fully dissociate; weak acids partially dissociate.
- Titration determines concentration; uses indicators and burettes for accuracy.
- Electrolysis uses electric current to break down ionic compounds; ions move to electrodes and are reduced/oxidized accordingly.
Energy Changes
- Exothermic reactions release energy (temperature increases); endothermic reactions absorb energy (temperature decreases).
- Activation energy is needed to start reactions.
- Energy profiles show the difference in energies of reactants and products.
- Bond energy calculations help determine the overall energy change.
Key Terms & Definitions
- Atom — Basic unit of matter with protons, neutrons, electrons.
- Isotope — Atom with same protons but different neutrons.
- Compound — Substance of two or more elements chemically bonded.
- Ion — Atom or molecule with a positive or negative charge.
- Relative formula mass (Mr) — Sum of atomic masses in a compound.
- Mole — Amount of substance containing Avogadro's number of particles.
- Redox — Reaction involving electron transfer (oxidation and reduction).
- Electrolysis — Breaking down ionic substances with electricity.
Action Items / Next Steps
- Review and practice balancing chemical equations.
- Memorize the key formulas: moles = mass / Mr, concentration = moles / volume.
- Complete practice questions on reactivity series, bonding types, and quantitative chemistry.
- (Triple) Practice titration calculations and electrolysis scenarios.
- Revise energy profile diagrams and bond energy calculations.