Overview
This lecture reviews core topics for GCSE Chemistry Paper 1, including atoms, bonding, chemical and energy changes, and crucial calculations.
Atoms and Elements
- An atom is the smallest unit that cannot be chemically broken down further.
- A compound contains two or more different atoms chemically bonded.
- A mixture contains different substances not chemically bonded.
- Separation methods include chromatography, filtration, and distillation.
Structure of the Atom and Periodic Table
- Atoms have a nucleus (protons and neutrons) and electrons in shells.
- Protons are +1, electrons are -1, neutrons are neutral; atoms are neutral when protons = electrons.
- The atomic number = protons; mass number = protons + neutrons.
- Electrons fill shells in the order 2, 8, 8, 2 (for first 20 elements).
- Periodic table groups show electrons in the outer shell; periods show the number of shells.
Bonding
- Metals tend to lose electrons (form positive ions); non-metals gain electrons (form negative ions).
- Ionic bonding: electrons transferred from metals to non-metals, forming charged ions.
- Covalent bonding: non-metals share electrons to fill their outer shells; can be simple molecules or giant covalent structures (diamond, graphite, graphene, fullerenes).
- Metallic bonding: metal atoms share a "sea" of delocalized electrons.
- Polymers are long chains of monomers joined together.
Chemical Changes
- Metal + oxygen → metal oxide (oxidation).
- Metal oxide + water → metal hydroxide + hydrogen.
- Acid + metal hydroxide → salt + water (neutralization).
- Thermal decomposition breaks compounds using heat.
- Displacement reactions occur when a more reactive metal replaces a less reactive one.
- Rust is iron oxide; other metals form other oxides.
- Blast furnace extracts iron from ore.
Quantitative Chemistry
- Law of conservation: atoms are not created or destroyed in reactions; equations must be balanced.
- Relative atomic mass (RAM) and moles: 1 mole = 6.02 × 10²³ particles.
- Moles = mass (g) / RAM.
- Solution concentration = mass or moles / volume (dm³).
- Percentage yield = actual mass / theoretical mass × 100.
- Atom economy = mass of desired product / total reactants × 100.
- 1 mole of any gas occupies 24 dm³.
- Titration measures the concentration of acids/bases using a burette, indicator, and conical flask.
Acids, Bases, and Electrolysis
- pH scale: 1 (acidic) to 14 (alkaline), 7 is neutral.
- Strong acids fully dissociate in water; weak acids do not.
- Electrolysis splits compounds using electric current; positive ions go to cathode (reduction), negative ions to anode (oxidation).
- Oxidation is loss of electrons; reduction is gain (OILRIG).
- Electrolysis can purify metals.
Energy Changes
- Exothermic reactions release energy (get hot); endothermic absorb energy (get cold).
- Activation energy is required to start a reaction.
- Energy change = bonds broken - bonds formed.
- Use specific heat capacity (SHC) equation to calculate energy in experiments.
Cells and Fuel Cells (Triple Science)
- Electrochemical cells generate voltage from two metals in ion solutions, connected by a salt bridge.
- Hydrogen fuel cells react hydrogen and oxygen to produce water and electricity with no CO₂ emissions.
Key Terms & Definitions
- Atom — Smallest unit of matter, cannot be chemically broken down.
- Ion — Atom or molecule with a net electric charge.
- Mole — 6.02 × 10²³ particles of a substance.
- Ionic bond — Chemical bond formed by electron transfer.
- Covalent bond — Chemical bond where atoms share electrons.
- Electrolysis — Splitting compounds with electricity.
- Exothermic — Reaction that releases energy.
- Endothermic — Reaction that absorbs energy.
- Oxidation — Loss of electrons.
- Reduction — Gain of electrons.
Action Items / Next Steps
- Practice balancing chemical equations.
- Complete sample calculations for moles, percentages, and concentrations.
- Review drawing dot and cross diagrams for bonding.
- Attempt practice questions, especially those involving math and practical methods.