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Chemistry Specification
17 sections · comprehensive exam board content overview
- Nucleus composition: An atom consists of a nucleus (protons + neutrons) surrounded by electrons in energy levels
- Particle properties: Proton: +1 e, mass ≈ 1 u; Neutron: neutral, mass ≈ 1 u; Electron: −1 e, mass ≈ 0 u
- Atomic number (Z): Number of protons
- Mass number (A): Protons + neutrons
- Electron configuration (first 20 elements): Comma-separated shells: H: 1, He: 2, Li: 2,1, Be: 2,2, ... Ca: 2,8,8,2
| Group | Representative Elements | General Property |
|---|---|---|
| 1 (Alkali) | Li, Na, K | Highly reactive metals, +1 oxidation state |
| 2 (Alkaline Earth) | Mg, Ca | Reactive metals, +2 oxidation state |
| 16 (Chalcogens) | O, S | Non-metals, −2 oxidation state |
| 17 (Halogens) | F, Cl, Br, I | Very reactive non-metals, −1 oxidation state |
| 18 (Noble gases) | He, Ne, Ar | Inert gases, full outer shells |
- Period: Horizontal row; Group: Vertical column
- Elements in same group share valence-electron configuration → similar chemistry
- Definition: Reactions rearrange atoms; nuclei remain unchanged
- State symbols: (s) solid, (l) liquid, (g) gas, (aq) aqueous
- Balancing: Ensures conservation of atoms; use ionic and half-equations for redox
| Concept | Formula / Approach |
|---|---|
| Molar mass (Mr) | Sum of atomic masses (g mol⁻¹) |
| Moles ↔ mass | n = m / Mr |
| % composition | (mass of element / total mass) × 100 |
| Empirical formula | Derive simplest whole-number ratio from % composition |
| Limiting reactant | Compare available moles with stoichiometric ratios |
| Gas volume (ideal) | V = 24 dm³ mol⁻¹ (rtp) |
| Concentration | c = n/V (mol dm⁻³) |
| Percentage yield | (actual / theoretical) × 100 |
- Oxidation: Loss of electrons (increase in oxidation state)
- Reduction: Gain of electrons (decrease in oxidation state)
- Redox reaction: Simultaneous oxidation & reduction
- Example: Mg (0) → Mg²⁺ (oxidation); 2H⁺ + 2e⁻ → H₂ (reduction)
- Disproportionation: Single species undergoes both oxidation and reduction
| Type | Key Features |
|---|---|
| Ionic | Transfer of electrons; opposite ions attracted; high melting points, conduct when molten |
| Covalent (Molecular) | Sharing of electrons; low melting points; discrete molecules |
| Covalent (Giant) | Extended network (e.g., diamond, SiO₂); high melting points |
| Metallic | Delocalised electrons; good conductivity, malleable |
- Roman numerals denote oxidation state for transition-metal ions (e.g., Fe(III) = Fe³⁺)
- Alkali metals: Reactivity ↑ down group (Li < Na < K)
- Halogens: Reactivity ↓ down group (F > Cl > Br > I)
- Displacement reaction example: Cl₂ + 2Br⁻ → 2Cl⁻ + Br₂ (Cl displaces Br)
| Technique | Principle |
|---|---|
| Distillation | Boiling-point differences |
| Fractional distillation | Repeated condensation/evaporation for close boiling points |
| Chromatography | Differential affinity; Rf = distance moved by solute / distance moved by solvent |
| Centrifugation | Density differences under rapid rotation |
| Filtration | Solid-liquid separation via porous medium |
- Acids: Donate H⁺; Bases: Accept H⁺ (or produce OH⁻)
- Strong vs. weak: Complete vs. partial ionisation in water
- pH: pH = −log[H⁺]; a change of 1 unit = 10-fold [H⁺] change
| Acid type | Example | H⁺ donors |
|---|---|---|
| Monoprotic | HCl | 1 |
| Diprotic | H₂SO₄ | 2 |
| Polyprotic | H₃PO₄ | 3 |
- Neutralisation: H⁺ + OH⁻ → H₂O (exothermic)
- Factors affecting rate: ↑ concentration, ↑ temperature, ↓ particle size, catalyst present, ↑ pressure (gases)
- Collision theory: Effective collisions → sufficient energy (activation energy Eₐ) and proper orientation
- Energy diagram: Reactants → peak (Eₐ) → products; catalysts lower Eₐ
- Exothermic: ΔH < 0 (heat released)
- Endothermic: ΔH > 0 (heat absorbed)
- Calorimetry: q = mcΔT (heat = mass × specific heat × temperature change)
- Bond energy: Energy absorbed to break bonds minus energy released to form bonds
| Electrode | Process |
|---|---|
| Cathode (−) | Reduction: cations gain electrons |
| Anode (+) | Oxidation: anions lose electrons |
- DC required: For directed ion movement
- Half-equations: Illustrate electron flow; e.g., Cu²⁺ + 2e⁻ → Cu (cathode)
- Alkanes: CₙH₂ₙ₊₂; Alkenes: CₙH₂ₙ (one C=C)
- Isomerism: Same molecular formula, different structural arrangement
- Polymerisation: Monomer (C=C) → polymer (addition) or condensation (loss of small molecule)
- Functional groups: Characteristic reactions (e.g., alcohols + Na → H₂)
| Functional Group | General Formula | Typical Reaction |
|---|---|---|
| Alcohol | R-OH | Reacts with Na → H₂ |
| Carboxylic acid | R-COOH | Forms salts with bases |
| Ester (from acid + alcohol) | R-COO-R' | Fragrance, hydrolysis yields acid + alcohol |
- Reactivity series: Determines displacement ability (e.g., Zn + H₂SO₄ → ZnSO₄ + H₂)
- Transition metals: Variable oxidation states, coloured compounds, catalytic ability
- Solid: Fixed positions, vibrational motion
- Liquid: Close packing, free movement
- Gas: Widely spaced, rapid random motion; PV = nRT (ideal gas law)
| Test | Observation | Substance Identified |
|---|---|---|
| Hydrogen (pop) | Squeaky pop with burning splint | H₂ |
| Oxygen (re-ignite) | Glowing splint relights | O₂ |
| Carbon dioxide (limewater) | Cloudy precipitate | CO₂ |
| Chlorine (bleaching) | Blue litmus → red then white | Cl₂ |
| Silver nitrate (halides) | White (Cl⁻), cream (Br⁻), yellow (I⁻) precipitate | Halide ions |
| Flame test | Colour characteristic (Li-crimson, Na-yellow, K-lilac, Ca-orange-red, Cu-green) | Metal cations |
- Dry air composition: 78% N₂, 21% O₂, 1% Ar, trace gases
- Greenhouse gases: CO₂, CH₄ trap infrared radiation → warming
- Water treatment: Chlorine → disinfection; fluoride → cavity prevention