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LOWER SEC SCIENCE SEC 2

Sec 2 Chemistry
Visual Notes

Pictures first. Formulas boxed. Every exam keyword highlighted.
HOW TO STUDY WITH THIS
Read the 💡 box
the whole topic in 1 line
Study the diagram
cover it, redraw it
Learn the yellow
formulas & keywords
Redo the worked example
without looking
THE CHAPTERS
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CH 1
Particulate Nature of Matter
Particles always move.
⚛️
CH 2
Atoms & Molecules
Formula = which atoms, how many.
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CH 3
Chemical Changes
New substance forms.
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CH 4
Acids & Alkalis
pH < 7 acid, > 7 alkali.
📌 NOTESchools order Lower Sec Science differently — some teach these chapters in Sec 1.
🖨 PRINTCtrl+P → Save as PDF · Scale 100% · Margins None · Background graphics ON
Chemistry · Sec 2 (Lower Sec Science)
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1

Particulate Nature of Matter

states, changes of state, expansion, diffusion
BIG IDEAAll matter is made of tiny particles that are always moving. Heat makes them move faster.
SOLID 🧊 packed · vibrate in place
LIQUID 💧 close, random · slide past
GAS 💨 far apart · move fast, randomly
SOLID LIQUID GAS melting freezing boiling /evaporation condensation
red = takes in heat · blue = gives out heat
Explain with particles
Expansion: heated particles move faster and further apart (particles do NOT get bigger)
Diffusion: particles move from high to low concentration (smell of perfume spreads)
Gas pressure: particles hit the walls
Mass is conserved: no particles are made or destroyed
⚠ TRAPWhen a solid expands, the particles stay the same size — only the spaces between them get bigger.
Chemistry · Sec 2 (Lower Sec Science)
⚛️
2

Atoms & Molecules

structure of atoms, symbols, formulae
BIG IDEAAn atom is the smallest particle of an element. A molecule is 2 or more atoms chemically joined.
nucleus: protons + neutrons · shells: electrons
ParticleChargeWhere
proton+1nucleus
neutron0nucleus
electron−1shells
Molecules
element molecules: O₂, N₂, H₂ (same atoms)
compound molecules: H₂O, CO₂ (different atoms)
Read a formula
H₂SO₄ → 2 H, 1 S, 4 O = 7 atoms
Ca(OH)₂ → 1 Ca, 2 O, 2 H
SymbolElementSymbolElementSymbolElement
HhydrogenNasodiumFeiron
CcarbonMgmagnesiumCucopper
NnitrogenAlaluminiumZnzinc
OoxygenClchlorineAgsilver
SsulfurKpotassiumCacalcium
🧠 HOOKIons: atoms that lose electrons become positive (Na⁺); atoms that gain electrons become negative (Cl⁻).
Chemistry · Sec 2 (Lower Sec Science)
🔥
3

Chemical Changes

word equations, types of reactions
BIG IDEAA chemical change makes a new substance. Atoms are rearranged, never created or destroyed.
Physical changeChemical change
New substance?noyes
Reversible?usually easyusually hard
Examplesmelting ice, dissolving sugarburning, rusting, cooking an egg
👀 Signs of a chemical change
gas bubbles (effervescence) · colour change · temperature change · precipitate forms · light/sound
Word equations
reactants → products
magnesium + oxygen → magnesium oxide
TypeWord equation
🔥 Combustionmethane + oxygen → carbon dioxide + water
🌡 Thermal decompositioncalcium carbonate → calcium oxide + carbon dioxide
🟤 Oxidation (rusting)iron + oxygen + water → rust
⚖️ Neutralisationacid + alkali → salt + water
🫁 Respirationglucose + oxygen → carbon dioxide + water + energy
🌿 Photosynthesiscarbon dioxide + water → glucose + oxygen (light, chlorophyll)
⚠ TRAPTotal mass before = total mass after (conservation of mass). If mass seems to drop, a gas escaped.
Chemistry · Sec 2 (Lower Sec Science)
🍋
4

Acids & Alkalis

pH, indicators, neutralisation
BIG IDEApH below 7 = acid, 7 = neutral, above 7 = alkali. Acid + alkali → salt + water.
01234567891011121314
◀ very ACIDICslightly acidicNEUTRAL 7slightly alkalinevery ALKALINE ▶
AcidAlkali
Taste / feelsourbitter, soapy
Litmusturns redturns blue
Universal Indicatorred / orange / yellowblue / violet
Examplesvinegar, lemon juice, HClsoap, NaOH, ammonia
ReactionProducts
acid + metalsalt + hydrogen
acid + carbonatesalt + water + CO₂
acid + alkalisalt + water
🦷 Everyday neutralisation
antacid tablets for indigestion · toothpaste (alkaline) vs mouth acid · lime for acidic soil · baking soda on bee stings
⚠ TRAPAcids and alkalis are corrosive. Use goggles; add acid to water, not water to acid.
Chemistry · Sec 2 (Lower Sec Science)