OCR GCSE Chemistry A: Properties of materials (J248) – Revision Notes

These revision notes condense sub-topic C2.3 Properties of materials of OCR GCSE (9-1) Chemistry A (Gateway Science), following OCR’s Version 4.0 J248 specification (August 2026). Statements C2.3a to C2.3j, mathematical outcomes CM2.3i to CM2.3vi and the dissolving tablets practical suggestion (PAG C8) are all here. Both tiers can be tested on every C2.3 statement, since none is Higher Tier only; the content sits on Paper 1 for Foundation candidates and Paper 3 for Higher. C2.3g to C2.3j and CM2.3ii to CM2.3vi are separate-chemistry content, in this course but not in combined science.

The study guide explains each idea at length; once these notes feel secure, move on to the practice questions. Also useful: the OCR GCSE Chemistry hub, a J248 checklist to print and our diagnostics, each about 10 minutes and free.

C2.3a and C2.3b: why carbon is special

• Carbon has four outer electrons and forms four covalent bonds.
• Carbon bonds strongly to other carbon atoms, so it forms chains (straight or branched), rings and families of similar compounds where each member differs by CH₂.
• Result: a vast number of natural compounds (in living things) and synthetic compounds (plastics, medicines, fuels).

Answer pattern for “explain why there are so many carbon compounds”: four bonds per carbon + bonds to other carbons + chains and rings of different lengths + families of similar compounds.

C2.3c: forms of carbon

	Diamond	Graphite	Graphene	Fullerenes
Bonds per C	4	3	3	3
Structure	Giant 3D tetrahedral network	Giant; stacked hexagonal sheets	A lone graphite sheet	Molecules: hollow spheres (C₆₀) or tubes
Conducts?	No	Yes, along layers	Yes	Nanotubes yes
Hardness	Very hard	Soft, slippery	Very strong, flexible	C₆₀ soft; nanotubes strong
Key reason	No delocalised electrons; every bond strong	Weak forces between layers; one delocalised electron per C	Strong bonds across sheet; delocalised electrons	C₆₀: weak forces between molecules

CM2.3i reminder. In a flat drawing of diamond, a carbon with four lines is a tetrahedron in 3D. In graphite, the space between sheets in a drawing is a region of weak forces, not empty “nothing”. To identify a structure from a model, count bonds on one carbon and check whether it continues (giant) or closes into a cage (molecule).

C2.3d: changes of state

Method in steps for “explain why X has a higher boiling point than Y”:

1. Name the structure of each substance.
2. Say what must be overcome: intermolecular forces (simple molecules) or strong bonds (giant structures).
3. Compare strength: stronger forces or bonds need more energy.
4. Conclude: more energy needed, so a higher temperature.

Must-know facts:

• During melting or boiling, the temperature stays constant while energy overcomes forces.
• Boiling a simple molecular liquid does not break covalent bonds inside its molecules.
• Bigger simple molecules: stronger intermolecular forces, higher boiling point.
• Freezing and condensing transfer energy out to the surroundings.

C2.3e: predicting states

Temperature compared with data	State
Below mp	Solid
Between mp and bp	Liquid
Above bp	Gas

Small reminder. Use these values: mp 80 °C, bp 218 °C. At 150 °C the substance is above its mp but below its bp, so it is a liquid. Range over which it is liquid: 218 − 80 = 138 °C.

Watch negative numbers. −50 °C is higher than −120 °C. A substance with bp −35 °C is a gas at −20 °C.

C2.3f: bulk properties from bonding

Structure	What holds it together	Melting point	Conducts?	Other
Ionic	Strong electrostatic attraction between ions in a giant lattice	High	Only molten or in solution	Brittle
Simple molecular	Weak intermolecular forces between molecules	Low	No	Often gas or liquid at room temperature
Giant covalent	Strong covalent bonds throughout	Very high	No (except graphite, graphene)	Hard (diamond)
Polymer	Covalent bonds in long chains; forces between chains	Usually solid at room temperature	No	Longer chains, stronger forces between chains
Metal	Metal cations with delocalised electrons around them	High	Yes, solid or liquid	Malleable

Must-know distinction: atoms do not have bulk properties. A single atom of a metal does not conduct or bend; one carbon atom is neither hard nor soft. Properties come from many atoms bonded and arranged together.

C2.3g: nano dimensions

Object	Typical size
Atom	radius about 0.1 nm (1 × 10⁻¹⁰ m)
C₆₀ molecule	about 1 nm across
Nanoparticle	1 nm to 100 nm
Unit conversion	1 nm = 1 × 10⁻⁹ m; 1 µm = 1000 nm

Method in steps for a size comparison:

1. Convert both sizes to the same unit (often metres in standard form).
2. Divide the larger by the smaller.
3. State “about … times larger”, with the number to a sensible precision.

Small reminder. A particle 16.8 nm across, atoms 0.28 nm across: 16.8 ÷ 0.28 = 60 atoms across.

C2.3h: surface area to volume

Quantity for a cube of side x	Formula
Surface area	6x²
Volume	x³
Surface area : volume	6 ÷ x

• Smaller particles: larger surface area to volume ratio.
• Side 10 times smaller: ratio 10 times larger.
• More surface exposed means faster reactions and dissolving, so nanoparticles can make better catalysts.

Small reminder. Cube of side 4 nm: area = 6 × 16 = 96 nm², volume = 64 nm³, ratio = 96 ÷ 64 = 1.5 nm⁻¹.

Dissolving tablets (PAG C8): independent variable is particle size (whole, broken, powdered); dependent variable is time to dissolve; control mass of tablet, volume of water and temperature. Repeat and take a mean, leaving out anomalies. Powdered tablets dissolve fastest.

C2.3i and C2.3j: uses and risks

Nanoparticle	Property	Use
Silver	Antibacterial	Wound dressings, socks
Titanium dioxide, zinc oxide	Block UV; no visible white layer	Sunscreens
Carbon nanotubes	Strong, light, conduct	Sports equipment, electronics
Many catalysts	High surface area to volume	Faster reactions with less material
Fullerene cages	Can hold other molecules	Drug delivery (in development)

Risks to quote, each linked to a property:

• Very small, so may be inhaled or pass through skin into cells.
• Large surface area, so may be more reactive or toxic than the bulk material.
• New materials, so long-term effects are not fully known.
• May reach the environment (for example in waste water) and harm organisms.

Quick self-test

1. How many covalent bonds does a carbon atom form?
2. Give two features of carbon compounds that explain why there are so many.
3. Why does graphite conduct electricity?
4. Why is C₆₀ softer than diamond?
5. Use these values: mp −39 °C, bp 357 °C. State the substance’s state at 0 °C.
6. When water boils, what is overcome?
7. Write 8 nm in metres, in standard form.
8. Is a particle 3.0 × 10⁻⁷ m across a nanoparticle? Show why.
9. A cube has edges of 8 nm. Find its surface area to volume ratio.
10. How many times larger is the surface area to volume ratio of a 3 nm cube than that of a 75 nm cube?
11. Why does a single metal atom not conduct electricity?
12. Give one property-linked risk of nanoparticles in sunscreen.

Answers

1. Four.
2. Any two: carbon bonds to other carbon atoms; forms chains; forms rings; forms families of similar compounds.
3. Each carbon bonds to three others, leaving one delocalised electron per carbon that can move along the layers.
4. C₆₀ is made of separate molecules held by weak intermolecular forces; diamond is a giant network of strong covalent bonds.
5. Liquid (0 °C is between −39 °C and 357 °C).
6. The intermolecular forces between water molecules, not the covalent bonds inside them.
7. 8 × 10⁻⁹ m.
8. 3.0 × 10⁻⁷ m = 300 nm, which is more than 100 nm, so no.
9. 384 nm² ÷ 512 nm³ = 0.75 nm⁻¹.
10. Ratios are 6 ÷ 3 = 2 and 6 ÷ 75 = 0.08; 2 ÷ 0.08 = 25 times.
11. Conduction is a bulk property: it needs a lattice of many metal ions with delocalised electrons moving through it. One atom has no such structure.
12. The particles are small enough to pass through skin or be inhaled, and their effects in the body are not fully known.

Where marks are usually lost

• Writing “bonds break” for boiling a simple molecular substance, instead of “intermolecular forces are overcome”.
• Saying graphite has “free ions” or “free atoms” instead of delocalised electrons.
• Describing C₆₀ as giant covalent; it is molecular.
• Giving only the property in a “use” question without linking it to why it suits the use.
• Writing “nanoparticles are dangerous” without naming a property (size, surface area) that causes the risk.
• Reading negative temperatures the wrong way round when predicting states.
• Mixing nm and m, or forgetting that 1 nm is 10⁻⁹ m, not 10⁻⁶ m.
• Stating that a smaller particle has a bigger surface area. It is the ratio (or the total area of many small pieces) that is bigger.
• Saying ionic compounds conduct when solid.

Official syllabus

OCR specification J248, Chemistry A (Gateway Science), Cambridge OCR Level 1/Level 2 GCSE (9-1): Version 4.0, August 2026; first assessment 2018. This page draws on sub-topic C2.3 Properties of materials.