Overview
This lecture provides a rapid review of all key topics for AQA GCSE Chemistry Paper 1, covering atomic structure, bonding, quantitative chemistry, chemical and energy changes, with notes on differences for triple and higher tier content.
Atomic Structure and the Periodic Table
- Atoms are basic units of elements; each element has a unique symbol on the periodic table.
- Compounds contain two or more different atoms chemically bonded; mixtures are not chemically bonded.
- Chemical equations must be balanced to conserve mass; use coefficients to balance atoms.
- Atoms have protons (+), neutrons (0), and electrons (-); protons and electrons have equal but opposite charges.
- Atomic number = number of protons; mass number = protons + neutrons.
- Isotopes are atoms of the same element with different neutron numbers.
- Electron shells fill in order: 2, 8, 8, 2 (up to calcium).
- Groups on the periodic table indicate number of outer electrons; metals on the left, non-metals on the right.
- Group 1 (alkali metals) get more reactive down the group; Group 7 (halogens) get less reactive down the group; Group 0 (noble gases) are unreactive.
Chemical Bonding
- Metallic bonding: lattice of positive ions and delocalized electrons (good conductors).
- Ionic bonding: metal donates electrons to non-metal, forming ions (positive cations, negative anions), forming high-melting-point crystals.
- Covalent bonding: non-metals share electrons to form molecules; double/triple bonds possible.
- Simple molecular structures have low melting points; giant covalent (e.g. diamond, graphite) have high melting points.
- Allotropes of carbon: diamond, graphite, graphene, fullerenes, nanotubes.
Quantitative Chemistry
- Conservation of mass: total mass stays the same in reactions.
- Relative atomic mass (RAM): weighted average; relative formula mass (RFM): sum of RAMs in compound.
- Moles (mol): amount of substance; moles = mass / RAM or RFM.
- Limiting reactant: substance that runs out first.
- Concentration: g/dm³ or mol/dm³; 1 dm³ = 1000 cm³.
- (Triple) Percentage yield = actual yield / theoretical yield x 100.
- (Triple) Atom economy = mass of desired product / total mass of reactants x 100.
- 1 mole of gas occupies 24 dm³ at room temperature and pressure (RTP).
Chemical Changes and Reactivity
- Reactivity series: more reactive metals displace less reactive ones from compounds.
- Displacement reactions predict which metals can be extracted by carbon or hydrogen.
- Oxidation = loss of electrons; reduction = gain of electrons (OIL RIG).
- Acids react with metals to form salts and hydrogen.
- Neutralization: acids (pH < 7) react with alkalis (pH > 7) to form salt + water.
- pH scale is logarithmic; strong acids fully dissociate, weak acids partially dissociate.
- (Triple) Titrations determine unknown concentrations using indicators and burettes.
Electrolysis
- Electrolysis splits ionic compounds using electricity; ions migrate to electrodes.
- Cations (positive) reduced at cathode; anions (negative) oxidized at anode.
- In solution, less reactive ion is discharged at electrode.
- Extraction of aluminum uses electrolysis with cryolite to lower melting point.
Energy Changes in Reactions
- Energy needed to break bonds (endothermic); energy released making bonds (exothermic).
- Exothermic: more energy released than absorbed (temperature rises).
- Endothermic: more energy absorbed than released (temperature falls).
- Energy profiles show changes in potential energy; activation energy is energy needed to start reaction.
- (Triple) Batteries and fuel cells generate voltage from chemical reactions; rechargeable batteries allow reverse reactions.
Key Terms & Definitions
- Atom — Smallest unit of an element.
- Isotope — Same element, different neutrons.
- Ion — Charged atom due to loss/gain of electrons.
- Mole (mol) — 6.02 × 10²³ particles of a substance.
- Limiting reactant — Substance that is used up first in a reaction.
- Electrolysis — Splitting substances using electricity.
- Exothermic — Releases energy to surroundings.
- Endothermic — Absorbs energy from surroundings.
- Neutralization — Acid + alkali → salt + water.
Action Items / Next Steps
- Practice balancing equations and calculating moles.
- Review the reactivity series and methods of extraction.
- Memorize key definitions and formulas.
- (Triple) Complete titration and energy profile calculation exercises.
- Prepare for practical questions on separation techniques and electrolysis.