GCSE AQA Chemistry

Atomic number

The number of protons in an atom's nucleus.

Mass number

The total number of protons and neutrons in an atom's nucleus.

Isotopes

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

Relative atomic mass (Ar)

The weighted average mass of an atom of an element

Ion

An atom or group of atoms that has lost or gained electrons

Cation

A positively charged ion

Anion

A negatively charged ion

Ionic bonding

The electrostatic attraction between oppositely charged ions

Covalent bonding

The sharing of electrons between two non-metal atoms.

Metallic bonding

The electrostatic attraction between positively charged metal ions and a 'sea' of delocalised electrons.

Giant ionic lattice

A regular

Macromolecular structure (Giant covalent structure)

A huge network of atoms held together by strong covalent bonds

Allotropes

Different structural forms of the same element in the same physical state

Mole

The amount of substance that contains $6.02 \times 10^{23}$ particles (Avogadro's constant).

Avogadro's constant

The number of particles ($6.02 \times 10^{23}$) in one mole of any substance.

Molar mass

The mass of one mole of a substance

Empirical formula

The simplest whole number ratio of atoms of each element in a compound.

Molecular formula

The actual number of atoms of each element in a molecule.

Limiting reactant

The reactant that is completely used up in a chemical reaction and therefore limits the amount of product that can be formed.

Atom economy

A measure of the amount of starting materials that are converted into useful products in a chemical reaction. Calculated as (mass of desired product / total mass of reactants) x 100.

Percentage yield

A measure of the efficiency of a chemical reaction. Calculated as (actual yield / theoretical yield) x 100.

Exothermic reaction

A reaction that releases energy to the surroundings

Endothermic reaction

A reaction that absorbs energy from the surroundings

Activation energy

The minimum amount of energy required for reactants to collide effectively and for a reaction to occur.

Catalyst

A substance that increases the rate of a chemical reaction without being used up in the reaction. It does this by providing an alternative reaction pathway with a lower activation energy.

Reversible reaction

A reaction where the products can react to reform the original reactants.

Dynamic equilibrium

In a reversible reaction

Le Chatelier's Principle

States that if a change in conditions is applied to a system at equilibrium

Acid

A substance that produces H+ ions in aqueous solution.

Base

A substance that neutralises an acid

Alkali

A soluble base that produces OH- ions in aqueous solution.

Salt

A compound formed when the hydrogen ion of an acid is replaced by a metal ion or ammonium ion.

Neutralisation reaction

The reaction between an acid and a base (or alkali) to form a salt and water.

pH scale

A scale from 0 to 14 that indicates the acidity or alkalinity of a solution. pH 7 is neutral

Strong acid

An acid that completely ionises in water

Weak acid

An acid that partially ionises in water

Strong base/alkali

A base/alkali that completely dissociates in water

Weak base/alkali

A base/alkali that partially dissociates in water.

Titration

A quantitative chemical analysis method used to determine the concentration of an unknown solution by reacting it with a solution of known concentration.

Oxidation

Loss of electrons

Reduction

Gain of electrons

Redox reaction

A reaction in which both oxidation and reduction occur simultaneously.

Oxidising agent

A substance that causes another substance to be oxidised (and is itself reduced).

Reducing agent

A substance that causes another substance to be reduced (and is itself oxidised).

Electrolysis

The process of using electrical energy to break down an ionic compound

Electrolyte

An ionic compound (molten or in solution) that conducts electricity due to the presence of free-moving ions.

Anode

The positive electrode in an electrolytic cell

Cathode

The negative electrode in an electrolytic cell

Anode in electrolysis of aqueous solutions

If halide ions are present

Cathode in electrolysis of aqueous solutions

If the metal is more reactive than hydrogen

Alloys

Mixtures of a metal with one or more other elements (usually metals) to improve its properties.

Corrosion

The destructive attack of a metal by reaction with substances in its environment

Sacrificial protection

A method of corrosion prevention where a more reactive metal is connected to the metal to be protected

Galvanising

Coating iron or steel with a layer of zinc to prevent rusting. The zinc acts as a barrier and provides sacrificial protection.

Crude oil

A finite mixture of hydrocarbons

Hydrocarbons

Organic compounds containing only hydrogen and carbon atoms.

Alkanes

Saturated hydrocarbons with the general formula $CnH{2n+2}$

Fractional distillation

The process used to separate crude oil into different fractions based on their boiling points.

Fractions of crude oil (from lowest to highest boiling point)

Refinery gases

Cracking

The process of breaking down long-chain hydrocarbon molecules into smaller

Alkenes

Unsaturated hydrocarbons with the general formula $CnH{2n}$

Test for unsaturation (alkenes)

Add bromine water. If an alkene is present

Polymers

Large molecules formed from many small repeating units called monomers.

Addition polymerisation

The process by which unsaturated monomers (alkenes) add together to form a long chain polymer

Thermosetting polymers

Polymers that do not melt when heated because they have strong cross-links between polymer chains.

Thermoplastic polymers

Polymers that soften and melt when heated because they have weak intermolecular forces between polymer chains

Combustion

A chemical process of burning

Complete combustion

Combustion in a plentiful supply of oxygen

Incomplete combustion

Combustion in a limited supply of oxygen

Greenhouse gases

Gases in the atmosphere that absorb and emit infrared radiation

Global warming

The gradual increase in the average temperature of the Earth's atmosphere and oceans.

Carbon footprint

The total amount of greenhouse gases (including carbon dioxide and methane) emitted over the full life cycle of a product

Potable water

Water that is safe to drink.

Hard water

Water containing dissolved mineral ions

Soft water

Water with a low concentration of dissolved mineral ions

Water purification methods

Filtration

Disadvantages of hard water

Forms scum with soap

Advantages of hard water

Contains beneficial minerals (calcium for teeth/bones)

Transition metals

Elements in the d-block of the periodic table

Alkali metals (Group 1)

Highly reactive metals

Alkaline earth metals (Group 2)

Reactive metals

Halogens (Group 7)

Reactive non-metals

Noble gases (Group 0)

Unreactive

Trends down Group 1

Reactivity increases (outer electron further from nucleus

Trends down Group 7

Reactivity decreases (outer shell further from nucleus

Test for hydrogen gas

Burns with a squeaky pop sound when a lighted splint is introduced.

Test for oxygen gas

Relights a glowing splint.

Test for carbon dioxide gas

Turns limewater (calcium hydroxide solution) cloudy.

Test for chlorine gas

Bleaches damp blue litmus paper white.

Test for ammonia gas

Turns damp red litmus paper blue.

Test for sulfate ions

Add dilute HCl

Test for halide ions (chloride

bromide

Bromide: cream precipitate

Iodide: yellow precipitate.

Test for carbonate ions

Add dilute acid. Effervescence (fizzing) observed

Test for ammonium ions

Add sodium hydroxide solution and warm. Ammonia gas is produced

Flame test for lithium ions

Crimson red flame.

Flame test for sodium ions

Strong orange flame.

Flame test for potassium ions

Lilac flame.

Flame test for calcium ions

Orange-red flame.