Overview
This lecture covers all essential content for AQA GCSE Chemistry Paper 1, including atoms, bonding, quantitative chemistry, chemical changes, and energy changes, for both double and triple science students.
Atomic Structure and the Periodic Table
- Atoms are the smallest units of elements, represented by symbols on the periodic table.
- Compounds contain two or more different atoms chemically bonded.
- Mixtures are physical combinations of elements or compounds not chemically bonded.
- Physical separation methods include filtration, crystallization, distillation, and fractional distillation.
- Solids, liquids, and gases differ by particle arrangement and energy.
- Chemical changes produce new substances; physical changes do not.
- Key atomic models: plum pudding (Thomson), nuclear (Rutherford), shell model (Bohr), discovery of neutrons (Chadwick).
- Atomic number = protons; mass number = protons + neutrons.
- Isotopes are atoms of the same element with different neutron numbers.
- Relative atomic mass is the weighted average of isotopes.
- Electron configuration fills shells as 2, 8, 8, 2.
- Group number indicates outer shell electrons; metals (left) lose electrons, non-metals (right) gain electrons.
Bonding and Structure
- Group 1 metals get more reactive down the group; Group 7 halogens get less reactive.
- Ions form by atoms gaining or losing electrons; metals form positive ions, non-metals form negative.
- Ionic bonding: transfer of electrons from metals to non-metals; compounds have high melting points and conduct electricity when molten or dissolved.
- Covalent bonding: sharing electrons between non-metals; forms molecules.
- Simple covalent compounds have low boiling points and do not conduct electricity.
- Giant covalent structures (e.g., diamond, graphite) have high melting points; graphite conducts electricity.
- Alloys are stronger than pure metals due to different atom sizes disrupting the lattice.
Quantitative Chemistry
- Conservation of mass: total mass remains constant during a reaction.
- Relative atomic/formula mass (RAM/Mr): sum of atomic masses.
- One mole = relative mass in grams.
- Moles = mass (g) / RAM or Mr.
- Limiting reactant controls the amount of product formed.
- Concentration = mass or moles per decimeter cubed (dm³).
- Percentage yield = (actual mass / theoretical mass) x 100; atom economy = (Mr of desired product / total Mr of reactants) x 100.
- One mole of gas occupies 24 dm³ at room temperature and pressure.
Chemical Changes
- Reactivity series ranks metals by reactivity; more reactive metals displace less reactive ones.
- Metals below carbon can be extracted by reduction; metals above require electrolysis.
- Oxidation = loss of electrons; reduction = gain of electrons (OIL RIG).
- Acids react with alkalis to make salt and water; neutralization occurs at pH 7.
- Strong acids fully dissociate; weak acids partially dissociate.
- pH scale is logarithmic.
Electrolysis
- Electrolysis splits ionic compounds using electricity; requires mobile ions (molten or in solution).
- Positive ions (cations) go to the negative cathode (reduced); negative ions (anions) go to the positive anode (oxidized).
- In solution, the least reactive cation is discharged at the cathode; halides discharge at the anode if present.
Energy Changes
- Breaking bonds needs energy; making bonds releases energy.
- Exothermic reactions release heat (products have less potential energy than reactants).
- Endothermic reactions absorb heat (products have more potential energy than reactants).
- Activation energy is needed to start a reaction.
- Bond energy calculations: energy in = bonds broken; energy out = bonds made; net energy = difference.
- Batteries and fuel cells generate voltage through chemical reactions.
Key Terms & Definitions
- Atom — Smallest particle of an element.
- Compound — Two or more different atoms chemically bonded.
- Isotope — Atom of the same element with different neutron counts.
- Ion — Atom with a charge due to gained or lost electrons.
- Ionic Bonding — Electron transfer between metals and non-metals.
- Covalent Bonding — Electron sharing between non-metals.
- Mole — Unit for amount of substance; Avogadro’s number.
- Relative Atomic Mass (RAM) — Average mass of atoms of an element.
- Reactivity Series — List of metals ordered by reactivity.
- Electrolysis — Splitting compounds using electric current.
- Exothermic — Reaction releases heat.
- Endothermic — Reaction absorbs heat.
Action Items / Next Steps
- Practice balancing chemical equations.
- Memorize group trends and key reactivity series.
- Revise calculation methods for moles, yield, and atom economy.
- Review example bond energy calculations.
- Complete chemistry practice questions on the topics above.