Overview
This lecture covers essential content for AQA GCSE Chemistry Paper 1, including key concepts from atomic structure, bonding, quantitative chemistry, chemical and energy changes, with distinctions for triple and higher tier content.
Atomic Structure and the Periodic Table
- Atoms consist of protons (+1), neutrons (0), and electrons (–1).
- The atomic number (bottom number) is the number of protons; mass number (top) is protons + neutrons.
- Isotopes are atoms of the same element with different numbers of neutrons.
- Ions form when atoms gain or lose electrons; gaining = negative ion, losing = positive ion.
- Early atomic models evolved from the plum pudding model to the nuclear model (Rutherford) and electron shells (Bohr).
Elements, Compounds, and Mixtures
- Elements are pure substances made of one type of atom; compounds contain chemically bonded different atoms.
- Mixtures are combinations of substances not chemically bonded and can be separated physically (filtration, crystallization, distillation).
- Word and symbol equations represent chemical reactions; equations must be balanced.
Bonding and Structure
- Metals bond through metallic bonding, forming a lattice of positive ions with delocalized electrons.
- Ionic bonding occurs when metals donate electrons to non-metals, forming ions.
- Covalent bonding is the sharing of electron pairs between non-metals.
- Simple covalent substances have low melting points; giant covalent (e.g. diamond, graphite) have high melting points and unique properties.
The Periodic Table and Groups
- Metals (left) lose electrons; non-metals (right) gain electrons.
- Group number = number of outer electrons (excluding transition metals).
- Group 1: Alkali metals, very reactive, more reactive down the group.
- Group 7: Halogens, less reactive down the group.
- Group 0: Noble gases, very unreactive.
Quantitative Chemistry
- The law of conservation of mass: total mass remains constant in reactions.
- Relative atomic mass (Ar) and relative formula mass (Mr) calculated by summing atomic masses.
- One mole = relative mass in grams.
- Moles = mass (g) / Mr or Ar.
- Stoichiometry shows the ratio of moles for reactants and products.
- Limiting reactant is the substance that runs out first in a reaction.
- Concentration = amount of solute per volume of solution, usually in mol/dm³.
Chemical Changes and Reactivity
- Reactivity series predicts if a metal will displace another from a compound.
- Metals less reactive than carbon can be extracted from oxides by reduction (smelting).
- Oxidation = electron loss; reduction = electron gain (OIL RIG).
- Acids (pH<7) react with alkalis (pH>7) to form salt and water (neutralization).
- Strong acids fully ionize; weak acids partially ionize.
Electrolysis
- Electrolysis uses electricity to split ionic compounds; requires liquid or aqueous state for ion movement.
- Cations move to the cathode (reduced); anions to anode (oxidized).
- In solution, the less reactive ion is discharged at the electrode.
- Electrolysis is used for metal extraction and purification.
Energy Changes
- Exothermic reactions release energy (temperature rises); endothermic reactions absorb energy (temperature falls).
- Activation energy is needed to start a reaction.
- Energy profiles show the change in potential energy during a reaction.
- Bond energies are used to calculate net energy change.
Key Terms & Definitions
- Ion — an atom or molecule with a net electrical charge.
- Isotope — atoms of the same element with different numbers of neutrons.
- Mole — unit for amount of substance, number of atoms/molecules as relative mass in grams.
- Stoichiometry — ratio of reactants and products in a chemical reaction.
- Electrolysis — process of using electricity to split ionic substances.
- Exothermic — reaction that releases energy.
- Endothermic — reaction that absorbs energy.
Action Items / Next Steps
- Review and practice balancing chemical equations.
- Memorize the reactivity series and group properties.
- Practice mole calculations and using the formula moles = mass/Mr.
- For triple students: study titrations and atom economy.
- Complete any assigned textbook readings or problems on these topics.