Overview
This lecture covers all essential topics for AQA GCSE Chemistry Paper 1, including atoms, bonding, quantitative chemistry, chemical and energy changes, for both Combined and Separate Science students.
Atoms and Elements
- Atoms are the smallest units of matter; elements consist of one type of atom.
- Compounds are substances made from two or more types of atoms chemically bonded.
- Chemical formulas indicate the types and numbers of atoms in a compound (e.g., H₂O).
- Chemical reactions rearrange atoms; the number of atoms on both sides must balance.
- Mixtures combine elements/compounds without chemical bonding and can be separated physically.
Separation and States of Matter
- Filtration, crystallization, distillation, and fractional distillation are physical separation techniques.
- Physical changes (melting, boiling) alter state but not chemical structure.
- State symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous (dissolved).
Atomic Structure and the Periodic Table
- Atoms consist of protons (+), neutrons (0), and electrons (-).
- The atomic number = number of protons; mass number = protons + neutrons.
- Isotopes are atoms with the same number of protons but different neutrons.
- Electron shells fill as 2, 8, 8, 2.
- Position in the periodic table indicates element type (metal/non-metal) and group reflects outer electrons.
Groups, Reactivity, and Ion Formation
- Group 1 (alkali metals): lose 1 electron, increase in reactivity down the group.
- Group 7 (halogens): gain 1 electron, decrease in reactivity down the group.
- Group 0 (noble gases): very unreactive with full outer shells.
- Metals form positive ions (cations), non-metals form negative ions (anions).
Chemical Bonding
- Metallic bonding: lattice of positive ions in a sea of delocalized electrons.
- Ionic bonding: metal donates electrons to non-metal, forming charged ions.
- Covalent bonding: non-metals share electrons to form molecules.
- Simple molecular structures have low boiling points; giant covalent structures (e.g., diamond) have high melting points.
Quantitative Chemistry
- Law of conservation of mass: total mass remains constant in reactions.
- Relative formula mass (RFM) is the sum of atomic masses in a compound.
- One mole = relative atomic/formula mass in grams.
- Moles = mass (g) / RFM; use mole ratios from equations to calculate reactants/products.
- Limiting reactant is used up first in a reaction.
- Concentration = mass or moles / volume (in dm³).
Percentage Yield and Atom Economy (Triple Only)
- Percentage yield = (actual mass / theoretical mass) × 100.
- Atom economy = (mass of desired product / total mass of reactants) × 100.
- At room temp and pressure, 1 mole of any gas occupies 24 dm³.
Chemical Changes and Reactivity
- Reactivity series ranks metals by reactivity; more reactive metals displace less reactive ones.
- Extraction by displacement (e.g., smelting) and reduction/oxidation (OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons).
- Acids react with metals to produce salt and hydrogen.
Acids, Alkalis, and the pH Scale
- Acids: pH < 7, release H+ ions; Alkalis: pH > 7, release OH- ions.
- Strong acids fully dissociate; weak acids partially dissociate.
- pH scale is logarithmic: each change in pH = 10× concentration change.
- Neutralization produces salt and water.
Electrolysis
- Electrolysis uses electricity to break compounds; cations go to cathode (reduced), anions to anode (oxidized).
- More reactive ions stay in solution; less reactive ones are discharged.
Energy Changes in Reactions
- Exothermic: releases energy, temperature increases (combustion).
- Endothermic: absorbs energy, temperature decreases.
- Activation energy is the minimum energy needed to start a reaction.
- Bond energies can be used to calculate overall energy change.
Cells and Batteries (Triple Only)
- Batteries produce voltage from two metals in an electrolyte.
- Non-rechargeable: reactants used up; rechargeable: reversed by supplied current.
- Hydrogen fuel cells produce electricity from hydrogen and oxygen.
Key Terms & Definitions
- Ion — an atom or molecule with a charge due to loss/gain of electrons.
- Isotope — atoms of the same element with different numbers of neutrons.
- Cation/Anion — positively/negatively charged ions, respectively.
- Relative Formula Mass (RFM) — sum of atomic masses in a compound.
- Mole — standard unit for amount of substance (6.02×10²³ particles).
- Concentration — amount of solute per unit volume of solution.
- OIL RIG — Oxidation Is Loss, Reduction Is Gain (of electrons).
- Electrolysis — process using electricity to decompose ionic substances.
Action Items / Next Steps
- Practice balancing chemical equations and calculating moles.
- Memorize the reactivity series and periodic table groups.
- Review types of bonding and properties of compounds.
- Complete all assigned textbook questions and practice papers.