Overview
This lecture covers all the essential content for AQA GCSE Chemistry Paper 1, focusing on atoms, bonding, quantitative chemistry, chemical and energy changes, with notes on differences for triple and higher-tier content.
Atoms and Elements
- Atoms are basic units of matter; elements are types of atoms, each represented by a symbol on the periodic table.
- Compounds are substances made of two or more different atoms chemically bonded.
- Chemical reactions rearrange atoms but conserve the total number of each kind; equations must be balanced.
Mixtures and Separation
- Mixtures are combinations of substances not chemically bonded (e.g., air, salt water).
- Filtration separates insoluble solids from liquids; crystallization and distillation separate solutes or liquids based on their boiling points.
- State changes (solid, liquid, gas) are physical, not chemical, changes.
Atomic Structure and Isotopes
- Atoms have a nucleus (protons and neutrons) and electrons in shells.
- Protons: +1 charge, mass 1; Neutrons: charge 0, mass 1; Electrons: -1 charge, negligible mass.
- Atomic number = protons; mass number = protons + neutrons.
- Isotopes are atoms of the same element with different numbers of neutrons.
Electronic Configuration and Periodic Table
- Electron shells fill 2, 8, 8, 2 up to calcium.
- Groups indicate number of outer electrons; metals (left) lose electrons, non-metals (right) gain.
- Reactivity trends: Group 1 metals get more reactive down the group; Group 7 halogens get less reactive.
Ions and Bonding
- Metals lose electrons to form positive ions (cations); non-metals gain electrons to form negative ions (anions).
- Ionic bonding: transfer of electrons from metals to non-metals; total charge in compounds must be zero.
- Covalent bonding: non-metals share electrons to form molecules; number of shared pairs = number of bonds needed.
Structure and Properties
- Ionic compounds: high melting/boiling points, conduct electricity when molten/dissolved.
- Simple molecular substances: low boiling points, do not conduct electricity.
- Giant covalent structures: high melting points (e.g., diamond, graphite).
- Metallic bonding: lattice of positive ions in a sea of delocalized electrons; good conductors.
Quantitative Chemistry
- Mass is conserved in reactions; equations must balance atoms.
- Relative atomic mass (Ar) and relative formula mass (Mr) calculated by adding atomic masses.
- Mole = amount of substance; moles = mass (g) / Ar or Mr.
- Limiting reactant: the reactant that is used up first in a reaction.
- Concentration: often measured in g/dm³ or mol/dm³.
Chemical and Energy Changes
- Reactivity series helps predict reactions and metal extractions.
- Displacement: more reactive metals displace less reactive metals from compounds.
- Oxidation = loss, reduction = gain of electrons (OIL RIG).
- Acids react with alkalis to form salts and water (neutralization); pH < 7 is acidic, > 7 is alkaline.
- Strong acids fully dissociate; weak acids partially dissociate.
- Electrolysis: passing electricity through ionic substances to decompose them; cations reduced at the cathode, anions oxidized at the anode.
Energy Changes
- Exothermic reactions release energy (temperature rises); endothermic absorb energy (temperature drops).
- Energy diagrams show potential energy of reactants/products; activation energy is the initial energy input needed.
- Bond energies determine the heat change; total energy in vs. out = net enthalpy change.
Key Terms & Definitions
- Atom — Basic unit of matter, makes up elements.
- Compound — Substance formed from two or more elements chemically bonded.
- Ion — Atom or molecule with a net charge due to loss/gain of electrons.
- Isotope — Atoms of the same element with different numbers of neutrons.
- Mole — Unit for amount of substance, linked to Ar/Mr.
- Cation — Positively charged ion (lost electrons).
- Anion — Negatively charged ion (gained electrons).
- Ionic Bonding — Electrostatic attraction between oppositely charged ions.
- Covalent Bonding — Sharing of electrons between non-metal atoms.
- Exothermic — Reaction that releases energy.
- Endothermic — Reaction that absorbs energy.
Action Items / Next Steps
- Practice balancing chemical equations.
- Memorize the reactivity series and common ions.
- Complete assigned exercises on moles, calculations, and energy profiles.
- Review differences between structure types (giant covalent, metallic, simple molecular).
- For triple students: Study titration methods and fuel cells.