Overview
This lecture summarizes all key topics for GCSE Chemistry Paper 1, covering atoms, bonding, the periodic table, chemical changes, quantitative chemistry, and energy changes.
Atomic Structure and the Periodic Table
- An atom is the smallest unit that can't be broken down by chemical means.
- A compound consists of two or more types of atoms chemically bonded together.
- A mixture contains different atoms or compounds not chemically bonded.
- Chromatography separates mixtures by capillary action on filter paper.
- Filtration separates insoluble substances; distillation separates dissolved solids from solvents.
- Atoms have a nucleus (protons + neutrons) and electrons in shells; number of protons = number of electrons in a neutral atom.
- Atomic number = protons; mass number = protons + neutrons.
- Electron shells fill as 2, 8, 8, 2 for the first 20 elements.
- Group number = outer electrons; period number = number of shells.
- Metals (left of the staircase) lose electrons; non-metals (right) gain electrons.
Bonding Types
- Ionic bonding: Metal donates electrons to non-metal, forming positive and negative ions.
- Ionic compounds form lattices, are soluble, have high melting points, and conduct electricity when molten or dissolved.
- Covalent bonding: Non-metals share electrons to get full outer shells; number of bonds = electrons needed.
- Simple covalent molecules (e.g., CH₄); giant covalent structures (e.g., diamond, graphite).
- Graphite conducts electricity due to delocalized electrons; graphene is a single layer.
- Metallic bonding: Lattice of ions with delocalized electrons leads to conductivity and malleability.
- Polymers are long chains of monomers joined, requiring pressure and a catalyst.
Chemical Changes and Reactivity
- Metal + oxygen → metal oxide (oxidation); metal + water → metal hydroxide + hydrogen.
- Acid + metal hydroxide → salt + water (neutralization).
- Thermal decomposition breaks down compounds with heat.
- Displacement reactions: more reactive metals replace less reactive ones in compounds.
- Rust is iron oxide formed from iron, oxygen, and water; other metals form different oxides.
- Blast furnace extracts iron from iron ore using carbon.
Quantitative Chemistry
- Law of conservation of mass: atoms are not created or destroyed in reactions; equations must be balanced.
- Relative atomic mass (RAM) and relative formula mass (RFM) from atomic mass numbers.
- A mole = 6.02 × 10²³ particles; moles = mass (g) / RAM or RFM.
- One mole of any gas occupies 24 dm³ at room temperature.
- Limiting reactant: reactant that runs out first, stopping the reaction.
- Solution concentration = amount of solute in grams or moles / volume in dm³.
- Percentage yield = (actual mass / theoretical mass) × 100%; atom economy = (mass of desired products / total mass of reactants) × 100%.
Analytical Chemistry
- Titration measures solution concentrations using a burette, indicator, and known volume of base.
- pH scale: 1 = strongly acidic, 7 = neutral, 14 = strongly alkaline.
- Strong acids fully dissociate in water; weak acids partially dissociate.
- Each decrease of 1 pH equals tenfold increase in [H⁺] ion concentration.
Electrolysis
- Electrolysis uses electricity to split compounds; anode = positive, cathode = negative.
- In brine, Cl⁻ goes to anode (forms Cl₂ gas), H⁺ to cathode (forms H₂ gas).
- Cations (positive ions) move to cathode; anions (negative ions) move to anode.
- Oxidation = loss of electrons; reduction = gain (OIL RIG); oxidation at anode, reduction at cathode.
- Electrolysis can purify metals like copper by transferring Cu²⁺ ions from anode to cathode.
Energy Changes in Reactions
- Exothermic reactions release more energy in bond making than consumed in bond breaking (temperature rises).
- Endothermic reactions absorb more energy to break bonds than released (temperature falls).
- Activation energy is needed to start reactions.
- Energy change = mass × specific heat capacity × temperature change.
- Bond energies can be used to calculate net energy change in reactions.
Redox and Electrochemical Cells
- Batteries use electrode potentials; connect two metals in electrolytes via a salt bridge to generate voltage.
- Fuel cells generate voltage by slowly reacting hydrogen and oxygen, producing water.
Key Terms & Definitions
- Atom — Smallest unit of an element, indivisible by chemical means.
- Compound — Substance of chemically bonded atoms of different elements.
- Ion — Atom or molecule with a net electric charge due to electron loss/gain.
- Mole — Amount containing 6.02 × 10²³ particles.
- Electrolysis — Process using electricity to decompose compounds.
- Oxidation — Loss of electrons.
- Reduction — Gain of electrons.
- Exothermic — Releases heat energy.
- Endothermic — Absorbs heat energy.
- Limiting Reactant — Reactant that is used up first, stopping the reaction.
Action Items / Next Steps
- Practice balancing chemical equations.
- Memorize group/period trends for reactivity.
- Complete example titration and calculation questions.
- Review definitions and bond energies for exam.