Chemistry Paper 1 glossary (AQA Trilogy)

alkali metal

A metal in Group 1 of the periodic table.

alpha particle scattering experiment

The experiment that suggested that the mass of an atom was concentrated in the centre (nucleus) and that the nucleus was charged. The experiment led to the nuclear model of the atom, which replaced the plum pudding model.

atom

The smallest part of an element that can exist.

atomic model

A model to represent the structure of the atom. This model has been revised over time as new evidence has become available.

atomic number

The number of protons in an atom of an element.

balanced equation

A representation of a chemical reaction using the formulae of the reactants and products. It shows the number of atoms of each element involved in the reaction.

ball and stick model

A model of a molecule that uses spheres to represent atoms and sticks to represent bonds.

charge

A property of a particle that causes it to experience a force in an electric field.

chemical change

A change in which one or more new substances are produced.

chemical formula

A series of chemical symbols showing the number of atoms of each element in a compound.

chemical reaction

A process that involves rearrangement of atoms to produce new substances.

chemical symbol

A letter or series of letters used to represent an element, e.g. C for carbon, Na for sodium.

chromatography

A technique used to separate substances based on their solubility in a particular solvent.

compound

A substance made up of two or more different elements chemically bonded together, e.g. water is a compound of hydrogen and oxygen.

crystallisation

A separation technique used to obtain a sample of pure salt from a salt solution.

dissolve

To mix a solute with a solvent to form a solution.

distillation

A technique to separate and collect a solvent from a solution.

electron

A particle with a relative charge of -1 and a very small relative mass. It orbits the nucleus of an atom or ion in energy levels (shells).

electronic structure

The number of electrons in each energy level (shell) of an atom, e.g. a sodium atom has an electronic structure of 2, 8, 1.

element

A substance made of only one type of atom.

energy level

The distance from the nucleus of an atom where electrons orbit. Also called a shell.

evaporation

A change of state from liquid to gas.

evidence

The available information or facts that either support or counter a scientific theory or hypothesis.

filtration

A technique used to separate substances that are insoluble in a particular solvent from those that are soluble in the solvent.

freezing

A change of state from liquid to solid.

gas

The state of matter in which a substance can flow and completely fill a container. It has no fixed shape or volume and can be compressed. The particles are far apart and move quickly in all directions. Shown as (g) in chemical equations.

groups

A column of the periodic table that contains elements with similar chemical properties.

halogen

An element in Group 7 of the periodic table.

inert

A substance that does not take part in chemical reactions.

insoluble

A substance that does not dissolve in a given solvent.

ion

A charged particle formed when an atom or molecule loses or gains one or more electrons.

isotopes

Atoms of the same element with different numbers of neutrons.

James Chadwick

The scientist who provided experimental evidence to show the existence of neutrons within the nucleus of an atom.

liquid

The state of matter in which a substance can flow and take the shape of a container. It has a fixed volume and cannot be compressed. The particles can move around each other. Shown as (l) in chemical equations.

mass number

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

melting

A change of state from solid to liquid.

melting point

The temperature at which a substance changes from solid to liquid (melts). It is also the temperature at which a substance changes from liquid to solid (freezes).

Mendeleev

The scientist who developed the periodic table. He left gaps for elements he predicted had not yet been discovered.

metal

An element that forms positive ions.

mixture

A substance consisting of two or more substances not chemically combined together, e.g. air is a mixture of nitrogen, oxygen, carbon dioxide and small amounts of other gases.

molecule

A substance made of more than one atom held together by covalent bonds.

nanometre

A unit of length equal to 10⁻⁹ metres.

neutron

A particle with no charge found in the nucleus of the atom. It has the same mass as a proton.

Niels Bohr

The scientist who adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances.

noble gas

An unreactive gas found in Group 0 of the periodic table.

non-metal

An element that forms negative ions.

nuclear model

The model of the atom suggested by Rutherford. In this model, the mass of the atom is concentrated at the nucleus, which is positively charged.

nucleus (plural: nuclei)

The centre of the atom, consisting of protons and neutrons. It is positively charged.

outer shell

The energy level of an atom furthest from the nucleus.

particle model

A model that describes the arrangement and movement of particles in a substance.

periodic table

A table of all the known the elements arranged in order of atomic number so that elements with similar properties are in columns, known as groups.

plum pudding model

Thomson's model of the atom that suggested that the atom is a ball of positive charge with negative electrons embedded in it.

product

A substance that is formed in a chemical reaction.

proton

A particle with a charge of +1 found in the nucleus of the atom. It has the same mass as a neutron.

radius

The distance from the centre to the circumference of a circle or sphere.

reactant

A substance that takes part in a chemical reaction.

relative atomic mass (Ar)

The average mass of an atom of an element that takes into account the abundance of the isotopes of the element.

relative formula mass (Mr)

The sum of the relative atomic masses of the atoms in a compound in the numbers shown in the formula.

Rf value

In chromatography, the ratio of the distance moved by a compound to the distance moved by the solvent.

shell

The distance from the nucleus of an atom where electrons orbit. Also called an energy level.

simple distillation

A technique used to separate a solvent from a solution.

solid

The state of matter in which a substance has a fixed shape and cannot flow or be compressed. The particles are close together in a regular arrangement. Shown as (s) in chemical equations.

solubility

A measure of the amount of substance that will dissolve in a certain volume of solvent.

soluble

A substance that will dissolve in a given solvent.

solute

The substance that dissolves in a solvent to make a solution. In salt water, this substance is the salt.

solution

A homogenous mixture of two or more substances, formed when a solute dissolves in a solvent. Salt water is an example.

solvent

The substance in which a solute dissolves. In salt water, this substance is the water.

state symbol

An abbreviation used in a symbol equation to show if a reactant or product is a solid (s), liquid (l), gas (g) or dissolved in water (aq).

state of matter

The classification of a substance as solid, liquid or gas.

symbol equation

An equation that uses the chemical formulae of the reactants and products to model a chemical reaction.

theory

A general explanation that applies to a wide range of situations and examples.

unreactive

A substance which does not react chemically.

volume

The amount of space that a substance or object occupies.

word equation

An equation that uses only the names of the reactants and products to model a chemical reaction.

alloy

A mixture of two or more elements, at least one of which is a metal. Examples include bronze and brass.

aqueous

A substance dissolved in water. Shown as (aq) in chemical equations.

aqueous solution

The mixture made by adding a soluble substance to water.

boiling

The process that happens at the boiling point of a substance when the rate of evaporation is at its maximum.

boiling point

The temperature at which a substance changes from liquid to gas (evaporates). It is also the temperature at which a substance changes from gas to liquid (condenses).

bond

An attraction between atoms, ions or molecules that enables the formation of chemical compounds. Such attractions could be ionic, covalent or metallic.

brittle

A material that breaks when stressed, rather than deforming.

Buckminsterfullerene

The first fullerene to be discovered. It has the chemical formula C₆₀ and a spherical shape.

carbon nanotube

A cylindrical fullerene with a very high length to diameter ratio.

change of state

A physical change from one state of matter to another.

condensation

A change of state from gas to liquid.

conduction

The transfer of heat or electricity through a material.

covalent bond

The attraction between two atoms that share one or more pairs of electrons.

delocalised electron

A bonding electron that is no longer associated with any particular atom and therefore free to move through the structure.

diamond

A giant covalent structure in which each carbon atom forms covalent bonds with four other carbon atoms.

dot and cross diagram

A diagram showing the arrangement of the outer shell electrons of the atoms or ions in a substance.

double bond

A type of bond where two pairs of electrons are shared between atoms.

electrostatic force

The attractive or repulsive force between two charged objects.

fullerene

A molecule of carbon atoms with a hollow shape. It has a cage-like structure based on hexagonal rings of carbon atoms.

giant covalent structure

A huge 3D structure made up of many atoms held together by covalent bonds.

giant ionic lattice

A huge 3D structure in which there are strong electrostatic forces of attraction in all directions between oppositely charged ions.

graphene

A single layer of graphite.

graphite

A giant covalent structure in which each carbon atom forms covalent bonds with three other carbon atoms, forming layers of hexagonal rings with no covalent bonds between the layers. One electron from each carbon atom is delocalised.

intermolecular forces

The attraction between individual molecules in a covalently bonded substance.

ionic bond

The electrostatic force of attraction between positively and negatively charged ions.

lattice

A closely-packed regular arrangement of atoms, ions or molecules.