Year 9 Chemistry Key Terms Summer 2026

Comprehensive vocabulary flashcards covering introductory chemistry concepts, states of matter, separation techniques, atomic structure, chemical bonding, and rates of reaction based on the Year 9 curriculum transcript.

Element

Made up of one type of atom (e.g., copper). These have a fixed melting and boiling point.

Compound

Made of two or more different atoms chemically bonded (e.g., water). These have a fixed melting and boiling point.

Mixture

Two or more different elements or compounds put together but not chemically bonded (e.g., air). Will melt/boil over a range of temperatures.

Atom

Tiny particles that make up everything, smallest particle of an element.

Molecule

Smallest particle that can have separate, individual existence. Metals and noble gases do not have molecules.

Metals

Conduct electricity; majority of the Periodic Table.

Non-metals

Do not conduct electricity; small section on the right-hand side of the Periodic Table (after the staircase).

Water

$$H_2O$$

Ammonia

$$NH_3$$

Methane

$$CH_4$$

Hydrochloric acid

$$HCl$$

Sulphuric acid

$$H_2SO_4$$

Nitric acid

$$HNO_3$$

(s) / (l) / (g) / (aq)

Solid / Liquid / Gas / Aqueous (solutions).

Chemical test for water

White anhydrous copper sulphate turns blue.

Physical test for water

Boils at $100${}^\circ\text{C}, melts at $0${}^\circ\text{C}.

Test for Oxygen

Relights a glowing splint.

Test for Hydrogen

Burns with a squeaky pop.

Test for Carbon dioxide

Bubble through limewater, which turns cloudy.

Test for Chlorine

Damp blue litmus paper turns red then bleaches.

Test for Ammonia (gas)

Damp red litmus paper turns blue.

Solid

Particles very close together (very strong forces), regular arrangement, particles have very little energy (only vibrate). Cannot be compressed.

Liquid

Particles very close together (forces between particles), random arrangement, particles have more energy and move around each other. Cannot be compressed.

Gas

Particles very far apart (no forces), random arrangement, particles have lots of energy and move very fast. Can be compressed.

Melting / Boiling

Particles gain energy. Phase changes: Solid to liquid / Liquid to gas.

Condensing / Freezing

Particles lose energy. Phase changes: Gas to liquid / Liquid to solid.

Sublimation

Solid straight to a gas, missing out the liquid state (e.g., carbon dioxide, iodine).

Diffusion

The spreading out of particles in a gas or liquid from an area of high concentration to low concentration.

$NH_3(g) + HCl(g) \rightarrow NH_4Cl(s)$ experiment

Forms a white cloud of ammonium chloride, appearing closer to the $HCl$ as it has a higher RFM and moves slower.

Simple distillation

Separates two liquids or a liquid from a dissolved solid when you want to keep the liquid; works due to different boiling points.

Fractional distillation

Separates out a mixture of liquids based on their different boiling points.

Filtration

Separates out insoluble solid from liquid/solution.

Crystallisation

Separates a dissolved solid from a liquid by evaporating off the liquid.

Rf value

$$\text{Rf} = \frac{\text{distance moved by the compound}}{\text{distance moved by the solvent}}$$

Saturated solution

Solution can take no more solute to dissolve (represented on the solubility curve).

Subatomic particle

Particles found within an atom.

Electron

Found in shells around the nucleus; Mass = $\frac{1}{1840}$; Charge = $-1$. Shell capacities: $2, 8, 8, 18$, etc.

Proton

Found in the nucleus; Mass = $1$; Charge = $+1$.

Neutron

Found in the nucleus; Mass = $1$; Charge = $0$.

Atomic number

The smaller number for each element; tells you the number of protons (and electrons in a neutral atom).

Mass number

The larger number for each element; tells you the number of protons plus neutrons.

Isotope

Atoms of the same element, with the same number of protons but different number of neutrons.

Relative atomic mass (RAM)

The weighted average mass of all isotopes of the element, measured on a scale where a carbon-12 atom has a mass of exactly $12$ units.

Groups and Periods

Groups (columns) indicate number of electrons in the outer shell; Periods (rows) indicate the number of shells with electrons.

Noble Gases

All have a full outer shell, meaning they are inert (not very reactive).

RFM (Mr)

The sum of all the RAMs of each element within the formula.

Moles Formula

$$\text{Moles} = \frac{\text{Mass (g)}}{\text{RAM or RFM}}$$

Ionic bonding

Strong electrostatic attraction between oppositely charged ions.

Covalent bonding

Strong electrostatic attraction between positive nuclei of each atom and the shared pair of electrons; occurs between non-metal atoms.

Diatomic molecule

Two of the same atom bonded together; e.g., $O_2, N_2, Cl_2, H_2$.

Rate of reaction

Change in concentration of reactant or product over a period of time; calculated as $\frac{\text{Change in concentration}}{\text{time}}$.

Activation energy

Minimum amount of energy required for a reaction to take place.

Catalyst

Increases the rate of reaction without being changed themselves by lowering the activation energy via an alternative pathway.