Chemistry (school) glossary
74 key terms from Chemistry (school), A to Z. Each is explained in one plain sentence and links to its free lesson.
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A
- AcidAcids, bases and salts
- A substance that forms hydrogen ions (H+) when it dissolves in water.
- AlkaliAcids, bases and salts
- A base that dissolves in water and forms hydroxide ions (OH-).
- Alkali metalsThe periodic table
- The soft, reactive metals of group 1: lithium, sodium and potassium.
- AlkaneCarbon chemistry and the Earth
- A hydrocarbon with only single bonds between carbon atoms.
- AlkeneCarbon chemistry and the Earth
- A hydrocarbon with a carbon-carbon double bond.
- AllotropeBonding and structure
- A different form of the same element, with its atoms arranged in a different pattern.
- AlloyBonding and structure
- A mixture of a metal with another element, usually another metal.
- AtomAtoms and matter
- The smallest piece of an element that still counts as that element.
- Atomic numberAtoms and matter
- The number of protons in an atom.
- Avogadro constantMoles and calculations
- The number of particles in one mole of any substance.
B
- Balanced equationChemical reactions
- A symbol equation with the same number of each type of atom on both sides.
C
- CatalystChemical reactions
- A substance that speeds up a reaction without being used up.
- Chemical reactionChemical reactions
- A change where atoms are rearranged to make one or more new substances.
- CombustionCarbon chemistry and the Earth
- Burning a substance in oxygen, which gives out energy.
- CompoundAtoms and matter
- A substance made of two or more different elements joined together by chemical bonds.
- ConcentrationMoles and calculations
- How much of a substance is dissolved in a given volume of solution.
- Conservation of massChemical reactions
- The total mass of the substances after a reaction equals the total mass before.
- Covalent bondBonding and structure
- A bond made when two atoms share a pair of electrons.
- CrackingCarbon chemistry and the Earth
- Breaking large hydrocarbon molecules into smaller, more useful ones, using heat and a catalyst.
- Crude oilCarbon chemistry and the Earth
- A thick dark liquid found underground, made from the remains of ancient sea creatures.
D
- Displacement reactionMetals and electrolysis
- A reaction in which a more reactive element pushes a less reactive element out of its compound.
E
- Earth's atmosphereCarbon chemistry and the Earth
- The layer of gases around Earth.
- ElectrolysisMetals and electrolysis
- Using electricity to split a molten or dissolved ionic compound into its elements.
- ElectrolyteMetals and electrolysis
- The molten or dissolved ionic compound used in electrolysis.
- ElectronAtoms and matter
- A tiny particle with a negative charge that moves around the nucleus.
- Electron shellThe periodic table
- A level around the nucleus that can hold a fixed number of electrons.
- ElementAtoms and matter
- A substance made of only one kind of atom.
- Endothermic reactionChemical reactions
- A reaction that takes in energy from the surroundings, so the temperature drops.
- Exothermic reactionChemical reactions
- A reaction that gives out energy to the surroundings, usually as heat, so the temperature goes up.
- Extraction by carbonMetals and electrolysis
- Metals less reactive than carbon, such as iron, are extracted by heating their oxide with carbon.
F
- Fractional distillationCarbon chemistry and the Earth
- A way to separate crude oil into fractions, groups of hydrocarbons with similar boiling points.
G
- Giant covalent structureBonding and structure
- A huge network of atoms joined by strong covalent bonds.
- Greenhouse effectCarbon chemistry and the Earth
- Gases such as carbon dioxide and methane trap heat in the atmosphere, keeping Earth warm.
- GroupThe periodic table
- A vertical column of the periodic table.
H
- HalogensThe periodic table
- The reactive non-metals of group 7, such as fluorine, chlorine, bromine and iodine.
- HydrocarbonCarbon chemistry and the Earth
- A compound made only of hydrogen and carbon atoms.
I
- IndicatorAcids, bases and salts
- A dye that changes colour depending on whether a solution is acidic or alkaline.
- IonBonding and structure
- An atom or group of atoms that has gained or lost electrons, so it carries an electrical charge.
- Ionic bondBonding and structure
- The strong attraction between a positive ion and a negative ion.
- Ionic latticeBonding and structure
- The regular, repeating 3D pattern of positive and negative ions in an ionic compound.
- IsotopeAtoms and matter
- Atoms of the same element with the same number of protons but different numbers of neutrons.
L
- Limiting reactantMoles and calculations
- The reactant that is used up first, which stops the reaction and limits how much product forms.
M
- Mass numberAtoms and matter
- The total number of protons plus neutrons in the nucleus of an atom.
- MetalThe periodic table
- An element that is usually shiny, hard, strong and a good conductor of heat and electricity.
- Metal and acid reactionAcids, bases and salts
- A reactive metal reacts with an acid to make a salt and hydrogen gas.
- Metallic bondingBonding and structure
- The attraction between positive metal ions and a sea of free electrons that move between them.
- MixtureAtoms and matter
- Two or more substances that are mixed but not chemically joined.
- Molar gas volumeMoles and calculations
- One mole of any gas takes up 24 dm3 at room temperature and pressure.
- MoleMoles and calculations
- The amount of a substance that contains 6.02 x 10^23 particles.
- Moles from massMoles and calculations
- To find the number of moles, divide the mass in grams by the relative formula mass.
N
- NeutralisationAcids, bases and salts
- The reaction between an acid and an alkali (or base) that makes a salt and water.
- NeutronAtoms and matter
- A particle inside the nucleus with no charge.
- Noble gasesThe periodic table
- The unreactive gases of group 0, such as helium, neon and argon.
- Non-metalThe periodic table
- An element that is usually dull, brittle when solid and a poor conductor.
O
P
- Percentage yieldMoles and calculations
- How much product you really made compared with the most you could have made.
- PeriodThe periodic table
- A horizontal row of the periodic table.
- pH scaleAcids, bases and salts
- A scale from 0 to 14 showing how acidic or alkaline a solution is.
- PolymerCarbon chemistry and the Earth
- A very long molecule made of many small repeating units (monomers) joined together.
- ProtonAtoms and matter
- A particle inside the nucleus of an atom with a positive charge.
R
- Rate of reactionChemical reactions
- How fast a reaction happens.
- Reactivity seriesMetals and electrolysis
- A list of metals in order of how readily they react.
- ReductionMetals and electrolysis
- A reaction where a substance loses oxygen or gains electrons.
- Relative atomic massMoles and calculations
- The average mass of an atom of an element compared with carbon-12 (which is 12).
- Relative formula massMoles and calculations
- The sum of the relative atomic masses of all the atoms shown in a formula.
- Reversible reactionChemical reactions
- A reaction that can go forwards and backwards.
- RustingMetals and electrolysis
- Iron reacting with oxygen and water to form hydrated iron oxide, a flaky orange-brown solid.
S
- SaltAcids, bases and salts
- A compound made when the hydrogen of an acid is replaced by a metal.
- Simple moleculeBonding and structure
- A small group of atoms joined by covalent bonds.
- State symbolsChemical reactions
- Small letters in brackets after a formula that show its state: (s) solid, (l) liquid, (g) gas and (aq) dissolved in water.
- Strong and weak acidsAcids, bases and salts
- A strong acid fully splits into ions in water.
T
- TitrationAcids, bases and salts
- A careful method that finds out exactly how much acid is needed to neutralise a measured amount of alkali, using a burette and an indicator.
- Transition metalsThe periodic table
- The block of metals in the middle of the periodic table, including iron, copper and zinc.