Overview
This lecture covers all core topics for AQA GCSE Chemistry Paper 1—including atoms, bonding, the periodic table, quantitative chemistry, chemical changes, energy changes, and some triple/ higher tier content.
Atoms, Elements, and Compounds
- Atoms are the basic units of matter; elements contain one type of atom, shown by symbols in the periodic table.
- Compounds are substances of two or more different atoms chemically bonded (e.g. Hâ‚‚O).
- Chemical reactions rearrange atoms; equations must be balanced as atoms are conserved.
- Mixtures consist of substances not chemically bonded and can be separated physically (e.g., filtration, crystallization, distillation).
Structure of the Atom & The Periodic Table
- Atoms have a nucleus of protons and neutrons, with electrons in shells outside.
- Protons (+1 charge), neutrons (0), electrons (-1); atomic number = protons, mass number = protons + neutrons.
- Isotopes are atoms of the same element with different numbers of neutrons.
- Early periodic tables used atomic weight; Mendeleev organized by properties and predicted undiscovered elements.
- Electron shells fill 2, 8, 8, 2 (up to calcium, then transition metals).
Groups, Periods, and Reactivity
- Metals (left) lose electrons to form positive ions; non-metals (right) gain electrons to form negative ions.
- Group number = electrons in outer shell; group 1 (alkali metals) are most reactive down the group, group 7 (halogens) less reactive down, group 0 (noble gases) unreactive.
- Transition metals can form multiple ions, are harder, and make colored compounds.
Types of Bonding and Structures
- Metallic bonding: lattice of ions with delocalized electrons; good conductors.
- Ionic bonding: metals transfer electrons to non-metals, forming crystal lattices with high melting points and electrical conductivity (liquid/solution).
- Covalent bonding: non-metals share electrons; simple molecules have low boiling points and don’t conduct electricity.
- Giant covalent structures (e.g., diamond, graphite) are very strong; graphite conducts electricity.
- Alloys are mixtures of metals, disrupting layers and making them stronger.
Quantitative Chemistry
- Relative atomic mass (RAM): average mass of isotopes.
- Relative formula mass: sum of RAMs in a compound.
- One mole = RAM in grams; moles = mass ÷ RAM.
- Limiting reactant is the first to run out in a reaction.
- Concentration: amount in g/dm³ or mol/dm³.
- (Triple) Percentage yield = (actual mass ÷ theoretical mass) × 100.
- (Triple) Atom economy = (desired product RAM ÷ total reactant RAM) × 100.
- One mole of gas at RTP = 24 dm³.
Chemical Changes
- Reactivity series shows how easily metals lose electrons; more reactive metals displace less reactive metals.
- Metals below carbon can be extracted by reduction with carbon; above need electrolysis.
- Oxidation = loss of electrons; reduction = gain (OIL RIG).
- Acids (pH<7) react with bases or alkalis (pH>7) to produce salts and water.
- pH scale is logarithmic; strong acids fully ionize, weak acids partially ionize.
Electrolysis
- Electrolysis splits ionic compounds using electricity; cations go to the cathode (reduced), anions to the anode (oxidized).
- In solution, less reactive ions are discharged.
- Aluminium extracted using electrolysis with cryolite to lower melting point.
Energy Changes
- Breaking bonds requires energy; making bonds releases energy.
- Exothermic reactions release net energy (temperature rises); endothermic reactions absorb net energy (temperature falls).
- Energy profiles show energy changes; activation energy is the initial energy input.
- (Triple) Cells and batteries generate voltage using chemical reactions; fuel cells generate electricity from hydrogen and oxygen.
Key Terms & Definitions
- Atom — smallest unit of an element.
- Isotope — same element, different neutrons.
- Ion — atom with a charge due to electron loss/gain.
- Mole — quantity containing Avogadro’s number of particles.
- Electrolysis — splitting compounds with electric current.
- Exothermic — releases heat energy.
- Endothermic — absorbs heat energy.
Action Items / Next Steps
- Memorize key equations for moles, atom economy, and energy change calculations.
- Practice balancing chemical equations and using state symbols.
- Review the reactivity series and methods of metal extraction.
- (Triple) Prepare examples for percentage yield and use of titration in concentration calculations.