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AQA A-level Chemistry Overview

Jun 15, 2025

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Overview

This lecture provides a comprehensive overview of AQA A-level Chemistry, covering foundational concepts, key definitions, calculations, bonding, organic chemistry, analytical techniques, and exam strategies.

Atomic Structure and Periodic Table

  • Atoms consist of protons (+1, mass 1), neutrons (0, mass 1), and electrons (-1, negligible mass).
  • Atomic number (Z) = number of protons; Mass number (A) = protons + neutrons.
  • Isotopes have same atomic number but different mass numbers due to varying neutrons.
  • Electron configuration is written as shells, subshells, and orbitals (e.g., 1s² 2s² 2p⁶).

Mass Spectrometry and Calculations

  • Mass spectrometry separates ions by mass/charge and helps identify relative atomic mass.
  • Relative atomic mass = (sum of (isotope abundance × mass))/100.
  • Key equations: moles = mass/Mr, PV = nRT (ideal gas law), and concentration = mass/volume.
  • Balancing equations requires accounting for atoms and state symbols.

Bonding and Structure

  • Ionic bonding: transfer of electrons between metals and nonmetals, forming charged ions.
  • Covalent bonding: sharing of electrons between nonmetals; includes dative and double/triple bonds.
  • Metallic bonding: delocalized electrons between positive metal ions.
  • Know properties of giant ionic, metallic, covalent, and simple molecular structures.

Chemical Calculations

  • Empirical formula: simplest whole number ratio of elements.
  • Molecular formula: actual number of atoms in a molecule.
  • Percent yield = (actual yield/theoretical yield) × 100.
  • Atom economy = (mass of useful products/total mass of reactants) × 100.

Periodicity and Groups

  • Periodic table organized by atomic number.
  • Group 2: Reactivity increases down the group, solubility trends in hydroxides and sulfates.
  • Group 7 (halogens): Reactivity decreases down group, displacement, and testing for halides.

Organic Chemistry Fundamentals

  • Definitions for empirical, molecular, structural, displayed, and skeletal formulae.
  • Nomenclature rules: find longest carbon chain, number to give lowest priority, use prefixes/suffixes.
  • Isomerism: chain, position, functional group, and E/Z (geometric) isomerism.
  • Reaction mechanisms: nucleophilic substitution, elimination, free radical substitution.

Analytical Techniques

  • Mass spectrometry: identifies molecular formula and fragments.
  • Infrared spectroscopy: identifies functional groups by characteristic absorption.
  • NMR (proton and carbon): chemical shift, integration, and splitting patterns to deduce structure.
  • Chromatography (TLC, column, gas): used to separate and identify compounds; Rf value = distance spot/distance solvent.

Acid-Base Equilibria and Electrochemistry

  • Acid: proton donor; Base: proton acceptor; pH = -log[H+].
  • Buffer solutions resist changes in pH with small additions of acid/base.
  • Standard electrode potentials and electrochemical cells explained; E°cell = E°(RHS) - E°(LHS).
  • Fuel cells, rechargeable batteries, and redox titration calculations.

Transition Metals

  • Exhibit variable oxidation states, form colored complex ions, and act as catalysts.
  • Complex ion structure: central metal ion with ligands; coordinate numbers dictate geometry.
  • Isomerism (cis/trans, optical) and ligand substitution can occur in complexes.
  • Catalysis: homogeneous and heterogeneous.

Key Terms & Definitions

  • Isotope — Atoms of same element with different neutrons.
  • Mole — Amount containing Avogadro's number (6.02 × 10²³) of particles.
  • Ionization Energy — Energy to remove one electron from each atom in a mole of gaseous atoms.
  • Electronegativity — Atom's ability to attract electrons in a bond.
  • Entropy (ΔS) — Measure of disorder.
  • ΔH — Enthalpy change; exothermic (-), endothermic (+).
  • Empirical Formula — Simplest ratio of elements in compound.
  • Buffer — Solution resisting pH change.
  • E/Z Isomerism — Geometric (cis/trans) isomerism due to restricted rotation around double bond.

Action Items / Next Steps

  • Review and practice key calculations (moles, yields, pH).
  • Memorize essential definitions and reaction mechanisms.
  • Complete exercises on spectroscopy and chromatography data interpretation.
  • Use provided revision guide, MCQs, and attend revision workshops as linked.

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