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Science KS4 Vocab


Dissolve in water to produce solutions with a ph of less than 7

Acid rain

Rain which has been made more acidic by pollutant gases

Activation energy

The energy needed for a chemical reaction to happen

Addition polymer

A very long molecule resulting from polymerisation, e.g. Polythene


Gravel added to cement and sand to make concrete

Alkali metals

The metals in group 1 of the periodic table


Compounds which produce hydroxide ions in water


A family of hydrocarbons with all single carbon-carbon covalent bonds and general formula ctn


A family of hydrocarbons with one double carbon-carbon bond and general formula


Different forms of the same element


A mixture of a metal with one or more other metals or non-metals to change the properties of the metal

Alpha particles

Radioactive particles which are helium nuclei – helium atoms without the electrons (they have a positive charge)


Meter used in an electric circuit for measuring current


Ion with a negative charge; they move to the anode during electrolysis


Electrode in electrolysis with a positive charge


Underground layer of permeable rock or loose materials (gravel or silt) where groundwater is stored


The basic ‘building block’ of an element, the smallest part of an element that can take part in a chemical reaction

Atomic number

The number of protons in the nucleus of an atom

Avogadro’s constant

The number of atoms, molecules or ions in one mole of a given substance, and is 6.02 x 1023 per mole

Balanced symbol equation

Chemical equation written in chemical symbols showing the number of atoms on each side of the equation balance


Reacts with an acid to form a salt


Process that uses bacteria to leach metal compounds from rocks

Biological catalyst

Molecules in cells of living organisms that speed up chemical reactions

Boiling point

Temperature at which the bulk of a liquid turns to vapour


A very stable spherical structure of 60 carbon atoms joined by covalent bonds (an allotrope of carbon)


An element present in all living things and forms a huge range of compounds with other elements


Radioactive isotope of carbon

Carbon dioxide (co2)

A greenhouse gas which is emitted into the atmosphere as a product of combustion

Carbon footprint

The total amount of carbon dioxide and other greenhouse gases emitted over the full life cycle of a product, service or event.


A chemical that speeds up a reaction but is not used up by the reaction


The negative electrode in electrolysis


A property of matter, charge exists in two forms, positive and negative, which attract each other

Chemical properties

The characteristic chemical reactions of substances


Addition of chlorine to water supplies to kill micro-organisms


A method for separating substances, used to identify compounds and check for purity

Close-packed atoms

Structure of many metals

Collision frequency

The number of collisions between particles that happen in one unit of time


Exothermic reaction of a substance with oxygen


Two or more elements which are chemically joined together, e.g. Hp


The amount of chemical dissolved in a certain volume of solution conductors materials which transfer thermal energy easily; electrical conductors allow electricity to flow through them

Conservation of energy

Principle stating that energy cannot be created or destroyed conservation of mass the total mass of reactants equals the total mass of products formed in a chemical reaction

Covalent bonds

Bonds between atoms where a pair of electrons is shared


The process of breaking down large hydrocarbons into smaller molecules

Curved line

Line of changing gradient


To rot or decompose

Delocalised electrons

Electrons which are free to move from atom to atom in a giant structure or a molecule


The density of a substance is its mass divided by its volume

Diesel oil

Fuel for diesel engines, traditionally obtained from crude oil but other forms such as biodiesel have been developed

Direct current

An electric current that flows in one direction only

Displacement reaction

Chemical reaction where an element takes the place of or ‘pushes out’ another element from a compound


The process of evaporation followed by condensation

Displayed formula

A representation of a molecule where every atom is shown by its symbol and the covalent bonds are shown as lines between the atoms

Dot and cross diagram

A diagram representing the number of electrons in the outer shell of atoms or ions

Electrical conductors

Materials that let electricity pass through them


Ions are discharged at the electrodes during electrolysis


The process of passing direct current through a melted ionic compound or a solution of an ionic compound so ions are discharged and the compound is broken down


A liquid or solution that conducts electricity and breaks down during electrolysis

Electronic structure

The arrangement of electrons in the sequence that they occupy the shells or energy levels, e.g. The 11 electrons of sodium are arranged 2,8,1


Small negatively charged particles within an atom that are outside the nucleus

Electrostatic attraction

Attraction between opposite charges, e.g. Between na+ and cl-


Substances made out of only one type of atom with the same number of protons in the nucleus

Empirical formula

Simplest ratio of atoms or ions in a compound

Endothermic reaction

Chemical reaction which takes in thermal energy


The ability to ‘do work’


Biological catalysts that increase the speed of chemical reactions


When the forwards and backwards reactions are occurring at the same rate in a closed system


Calculate approximately the value of something


When a liquid changes to a gas, it evaporates

Exhaust gases

Gases discharged into the atmosphere from an engine as a result of combustion of fuels

Exothermic reaction

Chemical reaction in which thermal energy is given out


A sudden, loud, violent release of energy by a chemical reaction


Making an estimate by continuing a trend or graph line beyond the range of results


How easy it is to light something on fire


A mixture that has been designed as a useful product

Fractional distillation

Crude oil is separated into fractions using this process of distillation where a mixture of liquids is vaporised and compounds with different boiling points condense at different temperatures


A push or pull which is able to change the velocity or shape of a body

Fossil fuels

Fuels which are the fossilised remains of plants or animals, such as coal, oil and gas


Cage-like carbon molecules containing many carbon atoms, e.g. Buckyballs

General formula of alkane


Giant covalent structure

A large regular arrangement of atoms all joined together by covalent bonds

Giant ionic lattice

The regular three-dimensional arrangement of ions in an ionic compound, also called a giant ionic structure


Rate of change of two quantities on a graph; change in y divided by change in x


A type of carbon made of layers of atoms

Greenhouse gas

Any of the gases whose absorption of solar radiation is responsible for the greenhouse effect, e.g. Carbon dioxide, methane


Within the periodic table the vertical columns are called groups. Group 1 the elements in group 1 of the periodic table, the alkali metals. Group 7 the elements in group 7 of the periodic table, the halogens

Half equation

A redox reaction is made up of two half equations, one in which electrons are lost and one in which electrons are gained.


Reactive non-metals in group 7 of the periodic table, e.g. Chlorine


Resistance of a solid material to cutting, indentation or scratching

Homologous series

A series of organic compounds that have the same general formula, i.e. The general formula of alkanes is cnh,,


Compounds containing only hydrogen and carbon

Incomplete combustion

Takes place when there is not enough oxygen present for complete combustion


Used to show ph of a solution or when the end point of a titration is reached

Insoluble salt

Salt which is not soluble in water intermolecular force force between molecules

Intermolecular forces

The attraction between two molecules


Making an estimate of a value from values on either side of the point

Ionic bond

The chemical bond between ions of opposite charges

Ionic equation

An equation showing changes to the ions involved in a reaction


Adds or removes electrons from an atom leaving it charged


Charged particles (can be positive or negative)


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


Unit of work done and energy

Kilogram (kg)

Unit of mass

Kinetic energy

The energy that moving objects have

Le chatelier’s principle

If a system is at equilibrium and a change is made to any of the conditions, then the system responds to counteract the change

Life cycle assessments

(lcas) are carried out to assess the environmental impact of products in each of the stages involved in their manufacture, use and disposal


A solution of calcium hydroxide in water – the colourless solution turns milky in the presence of carbon dioxide

Limiting reactant

Chemical used up in a reaction that limits the amount of product formed

Line spectrum

A spectrum produced by gaseous atoms showing individual lines at particular wavelengths that is unique for each element




To split apart


Size of something


The amount of matter in something; it is measured in kilograms (kg)

Mass number

The sum of the number of protons and neutrons in a nucleus

Melting point

The temperature at which a solid turns into a liquid

Metal halide

A compound of a halogen and a metal, e.g. Potassium bromide

Metallic bonding

The bonding between atoms in a metal due to delocalised electrons

Metallic properties

The physical and chemical properties specific to a metal, such as lustre, electrical conductivity and the ability to form positive ions


Elements with properties of both metals and non-metals; in the periodic table they are between the metals and non-metals


Elements that are usually solid, lustrous, conduct electricity and form ions by losing electrons


Natural solid materials with a fixed chemical composition and structure, rocks are made of collections of minerals

Mobile phase

In chromatography this is the phase that moves


A unit for a standard amount of a substance. One mole of any substance contains the same number of particles, atoms, molecules or ions as one mole of any other substance

Molecular formula

The formula of a chemical using chemical symbols, e.g. Methane has the molecular formula ch4


Two or more atoms covalently bonded to form the smallest unit of an element or compound, e.g. O2, h2o


A substance in its liquid state, often referring to a substance which is solid at ordinary temperatures, such as rock, ores, metals or salts, when heated to temperatures above its melting point

Negative ion

An ion with a negative charge, such as when atoms gain electrons


A neutral solution has a ph of 7


The reaction that takes place when an acid and base react to produce a salt and water


Particle which does not have a charge found in the nucleus of an atom


Elements that are solids, liquids or gases that do not conduct electricity and bond covalently or form negative ions by their atoms gaining electrons


Something which is used up at a faster rate than it can be replaced e.g. Fossil fuels


Central part of an atom that contains protons and neutrons

Optimum conditions

The conditions, such as temperature and pressure, that give the products of a chemical process at the lowest cost

Order of magnitude

Values that differ by one order of magnitude are 10 times larger or smaller than each other


When a reactant gains oxygen or loses electrons


Small particles in the air often caused by burning fuels


A row in the periodic table

Periodic table

A table of all the chemical elements in order of their atomic numbers


Volatile mixture of mainly hydrocarbons used as a fuel


Medical drugs

Physical property

Property that can be measured without changing the chemical composition of a substance, e.g. Hardness


Process that uses plants to extract metals


Substances that can cause damage to the environment


Put unwanted or harmful substances into the environment


Contamination of the environment as a result of human activities


Very large molecule formed from many similar smaller molecules (monomers) linked together

Positive ion

An ion with a positive charge, such as when atoms lose electrons

Potable water

Water that is safe to drink and has low levels of dissolved solids and microbes


Solid formed in a solution by a chemical reaction

Precipitation reaction

Chemical reaction in which a solid is formed when two solutions are mixed, e.g. In chemical tests for ions


Substance produced by a chemical reaction (shown on the right-hand side of the chemical equation)


Positively charged particles found in the nucleus of an atom


A pure substance is a single element or compound that is not mixed with any other substance


Having no regular pattern

Rate of reaction

The speed with which a chemical reaction takes place, measured by the amount of a reactant used or amount of product formed in a given time


Chemicals that react together in a chemical reaction (shown on the left-hand side of the chemical equation)


Battery or cell being charged with a flow of electric current


When a reactant loses oxygen or gains electrons


The refining process turns crude oil into usable forms such as petrol

Relative atomic mass

The mass of an atom compared to 1/12 of the mass of a carbon-12 atom

Relative formula mass

The sum of the relative atomic masses in a compound

Renewable energy

Energy from a resource that is rapidly replaced

Renewable resource

Any resource that can be replenished at the same rate that it is used, e.g. Biofuels


A water resource where large volumes of water are held

Reversible reaction

A chemical reaction where the reactants form products that, in turn, react together to give the reactants back


In chromatography is the distance a substance moved divided by the distance the solvent moved

Saturated hydrocarbon

A hydrocarbon containing the maximum number of hydrogen atoms and only single carbon-carbon bonds; alkanes are saturated hydrocarbons

Sea water

Water from the sea that contains high levels of dissolved salts making it undrinkable


A process during water purification where small solid particles are allowed to settle

Single covalent bond

Chemical bond between atoms where each atom shares one pair of electrons

Solar energy

Energy from the sun


A soluble substance can dissolve in a liquid, e.g. Sugar is soluble in water


When a solute dissolves in a solvent, a solution forms


The liquid used to dissolve a solute

Stable electronic structure

The electronic structure of a noble gas, with two electrons in the first shell and eight electrons in every other outer shell, e.g. He 2; ne 2,8; ar 2,8,8; kr 2,8,18,8

Standard form

A way of writing a large number with one number before the decimal point, multiplied by a power of 10, e.g. 1 200 = 1.2 x 103

Stationary phase

The phase in chromatography that does not move; in paper chromatography it is the paper

Straight line

Line of constant gradient

Strength (of an acid)

Strong acids ionise completely in water; weak acids partially ionise

Sub-atomic particles

Particles that make up an atom, e.g. Protons, neutrons and electrons


Change of state of a substance from a solid directly to a gas; e.g. Iodine

Thermal decomposition

The breaking down of a compound into two or more products on heating

Thermal energy

Energy that can be transferred as heat


A toxic substance is one which is poisonous and causes harm to living organisms

Transition element

An element in the middle section of the periodic table, between the block containing groups 1 and 2 and the block containing group 3 to group 0

Unsaturated hydrocarbon

A hydrocarbon containing fewer than the maximum number of hydrogen atoms possible, and so at least one double bond.


Space containing no particles of matter


The thickness of a liquid

Voltage (also called the potential difference)

The difference in electrical potential between two points or objects


Instrument used to measure voltage (potential difference)

Volt (v)

Unit used to measure voltage

Water conservation

Reducing water consumption through planned choice, e.g. Hosepipe bans and water metering

Water resources

Places from where water is extracted or where it is stored, e.g. Aquifers, reservoirs or lakes


Distance between two wave peaks or the distance between identical points in adjacent cycles of a wave

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