Chemistry Edexcel Terms

Anion

A negatively charged ion. Formed when an atom gains at least one electron.

Atom

The smallest part of an element that can exist. All substances are made up of atoms.

Atomic nucleus

Positively charged object composed of protons and neutrons at the centre of every atom with one or more electrons orbiting it.

Atomic number

The number of protons in the nucleus.

Avogadro’s constant

The number of atoms, molecules or ions in a mole of a given substance. 6.02 × 10²³

Cation

A positively charged ion. Formed when an atom loses at least one electron.

Compound

A substance made up of two or more types of atoms chemically combined together.

Concentration

The amount of substance (e.g. the mass) in a certain volume of a solution.

Conductor

A material that contains charged particles which are free to move to carry electrical or thermal energy.

Conservation of mass

A law which states that no atoms are lost or made during a chemical reaction so the mass of the products equals the mass of the reactants.

Covalent bond

A shared pair of electrons between two non-metals.

Dalton model

Dalton described atoms as solid spheres, stating that different spheres made up the different elements.

Diamond

A giant covalent structure which is made up of carbon atoms each of which form four covalent bonds with four other carbon atoms.

Electron

Negatively charged subatomic particle which orbit the nucleus at various energy levels. Mass of 0.005

Electron shell

Different energy levels in atoms occupied by electrons.

Electrostatic forces

The strong forces of attraction between oppositely charged ions.

Element

A substance made up of only one type of atom.

Empirical formula

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

Fullerenes

Molecules of carbon atoms with hollow shapes. The structures are based on hexagonal rings of carbon atoms but they may also contain rings with five or seven carbon atoms. Examples include graphene and C60.

Giant covalent molecule

Molecules containing many atoms covalently bonded together.

Graphene

A single layer of graphite with properties that make it useful in electronics and composites.

Graphite

A giant covalent structure which is made up of carbon atoms each of which form three covalent bonds with three other carbon atoms. The atoms form layers of hexagonal rings which have no covalent bonds between them. There is one delocalised electron per carbon atom which is free to move to carry charge.

Group (periodic table)

A column of the periodic table. Elements in the same group have similar chemical properties.

Intermolecular forces

The forces which exist between molecules. The strength of the intermolecular forces impact physical properties like boiling/melting point.

Ion

An atom or molecule with an electric charge due to the loss or gain of electrons.

Ionic bond

The bond formed between the oppositely charged ions when a metal atom loses electron(s) to form a positively charged ion and a non-metal gains these electron(s) to form a negatively charged ion.

Ionic compound

Chemical compound formed of oppositely charged ions, held together by strong electrostatic forces.

Isotope

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

Lattice

A repeating regular arrangement of atoms/ions/molecules. This arrangement occurs in crystal structures.

Limiting reactant

The reactant that is completely used up since it limits the amount of products formed.

Mass number

The total number of protons and neutrons in the nucleus.

Metallic bond

The bonds present in metals between the positive metal ions and negatively charged electrons.

Metals

Elements that react to form positive ions. Found to the left and towards the bottom of the periodic table.

Mole

The unit for amount of substance. The symbol for the unit mole is mol.

Molecular formula

The actual ratio of atoms of each element present in a compound.

Molecule

A group of at least two atoms held together by covalent bonds.

Neutron

Neutral subatomic particle present in the nucleus of the atom. Relative mass of 1.

Non-metals

Elements that react to form negative ions. Found towards the right and top of the periodic table.

Period (periodic table)

A row of the periodic table. Elements in the same period have the same number of electron shells.

Periodic table

Table of elements arranged in order of increasing atomic number and such that elements with similar properties are in the same column (group).

Polymers

Large long-chain molecules made up of lots of small monomers joined together by covalent bonds.

Proton

Positively charged subatomic particle present in the nucleus of the atom. Relative mass of 1.

Relative atomic mass

An average value that takes into account the abundances of the isotopes of the element.

Relative formula mass

The sum of the relative atomic masses of the atoms in the numbers shown in the formula. It is numerically equal to the mass of one mole of a substance in grams.

Simple molecules

Molecules containing a fixed number of atoms covalently bonded together.

Subatomic particles

Particles smaller than an atom. Protons, neutrons and electrons are the three most common subatomic particles.

Chlorination

A process used in water treatment where chlorine gas is injected into the water to kill any microbes.

Chromatography

A process used to separate substances in a mixture. Separation of the substance depends on distribution between a mobile phase and a stationary phase.

Crystallisation

A separation technique to obtain soluble solids from solutions. The process involves heating the solution until crystals start to form, leaving the solution to cool and then filtering the formed crystals from the solution.

Filtration

A separation technique used to separate an insoluble solid from a solution.

Fractional distillation

A process used to separate a mixture of liquids. The liquids have different boiling points so can be separated into different fractions within a fractionating column.

Gas

The state of matter where the particles have the most energy. The particles in a gas are relatively spread out and move randomly in all directions.

Ground water

Water which collects in rocks that then trap the water underground.

Liquid

The state of matter where the particles are arranged randomly and close together. The particles are able to move past each other.

Melting point data

Data which can be used to evaluate the purity of a substance. A pure substance should have a sharp melting point.

Mixture

Contains at least two different elements or compounds which are not chemically bonded together.

Mobile phase

The fluid (gas or liquid) which moves through the chromatography system, carrying the mixture which is to be separated.

Paper chromatography

A type of chromatography which uses paper as the stationary phase and a solvent as the mobile phase. The solvent carries the mixture up the paper where the substances in the mixture then separate, depending on how soluble they are in the mobile phase.

Particle theory

The theory which models the three states of matter by representing the particles as small solid spheres. Particle theory can help to explain melting, boiling, freezing and condensing.

Potable water

Water that is safe for humans to drink.

Pure substance

The chemistry definition of a pure substance is a substance which contains only one compound or element. The everyday definition of a pure substance is a substance which has nothing added to it, e.g. pure milk.

Rf value

A value used in chromatography which is calculated as the distance travelled by the dissolved substance divided by the distance travelled by the solvent. It can be used to identify substances within a mixture.

Sedimentation

A process used in water treatment to remove solids from the water. Suspended solids will fall to the bottom of the container and form a sediment, allowing them to be easily removed.

Simple distillation

A separation technique used to separate a liquid from a solution. The solution is heated so that only the liquid with the lowest boiling point evaporates. This gas is then condensed in a condenser before being collected as a liquid.

Solid

The state of matter where the particles hold a regular arrangement and have the least amount of energy.

State symbols

The symbols used in chemical equations to denote the states of the chemicals reacting

Stationary phase

The nonmoving phase which the mobile phase passes over during chromatography.

Waste water

Water from industrial, domestic, agricultural and commercial activity. It requires treatment before it is potable.

Acid

Produces hydrogen ions (H+) in aqueous solutions with a pH range between 0 and 7.

Alkali

Produces hydroxide ions (OH-) in aqueous solutions with a pH range between 7 and 14.

Anode

The positive electrode. It is where negatively charged ions lose electrons in oxidation reactions. It is the electrode where oxygen is produced unless the solution contains halide ions - then the halogen is produced.

Base

A substance which reacts with an acid in a neutralisation reaction to form a salt and water only.

Cathode

The negative electrode. It is where positively charged ions gain electrons in reduction reactions. It is the electrode where hydrogen is produced if the metal in the electrolyte is more reactive than hydrogen.

Electrode

A solid conductive material through which electricity can flow. They are used in electrolysis to conduct electricity.

Electrolysis

The splitting up of an ionic compound using electricity. The electric current is passed through a substance causing chemical reactions at the electrodes which lead to the decomposition of the materials.

Electrolyte

A solution containing free ions from the molten or aqueous ionic substance. The ions are free to move to carry charge.

Indicators

A chemical used in a titration reaction to identify the end point of the reaction by a clear colour change. Examples include phenolphthalein and methyl orange.

Neutralisation

The reaction in which an acid and a base react to form a salt and water.

Oxidation

A reaction involving the gain of oxygen. Oxidation is the loss of electrons.

pH scale

A measure of the acidity or alkalinity of a solution. The scale ranges from 0-14 and can be measured using universal indicator or a pH probe.

Reduction

A reaction involving the loss of oxygen. Reduction is the gain of electrons.

Strong acid

An acid which is completely ionised in an aqueous solution so that nearly all the H + ions are released. Examples of strong acids include hydrochloric, nitric and sulfuric acids.

Titration

A technique used where a solution of known concentration is used to determine the concentration of an unknown solution.

Universal indicator

A mixture of dyes that changes colour gradually over a range of pH and is used in testing for acids and alkalis.

Weak acid

An acid which is only partially ionised in an aqueous solution. This means only a small number of the H + ions are released. Examples of weak acids include ethanoic, citric and carbonic acids.

Bacterial extraction

A method of metal extraction which uses bacteria to extract metals from their ores. The bacteria breaks down low-grade ores to produce an acidic solution containing metal ions.

Cation

A positively charged ion. Metals tend to form cations. Formed when an atom loses at least one electron.

Displacement

A chemical reaction in which a more reactive element displaces a less reactive element from its compound.

Dynamic equilibrium

A reversible reaction will reach dynamic equilibrium when the rate of the forward reaction is equal to the rate of the backward reaction. At dynamic equilibrium, the concentration of reactants and products remains constant.

Electrolysis

The splitting up of an ionic compound using electricity. The electric current is passed through a substance causing chemical reactions at the electrodes which leads to the decomposition of the materials. Electrolysis is used for metal extraction if the metal is more reactive than carbon.

Haber process

An industrial process which produces ammonia from the reaction between nitrogen and hydrogen. The reaction conditions are 450oC and 200 atm and it requires an iron catalyst.

Life-cycle assessment

The analysis of the impact a product has on the environment. It considers the raw materials, manufacturing, packaging, transportation, product use and disposal.

Ore

A type of rock which contains metal compounds. The metals or metal compounds are present in sufficient amounts to make it worth extracting them.

Oxidation

A reaction involving the gain of oxygen. Oxidation is the loss of electrons.

Phytoextraction

A method of metal extraction which uses plants to absorb the metal compounds through their roots. The plants are then burned so that the metal compound can be removed from the ash.

Reactivity series

A series in which metals are arranged in order of their reactivity. This can be used to predict products from reactions.

Redox reaction

A reaction in which both oxidation and reduction occur simultaneously.

Reduction

A reaction involving the loss of oxygen. Reduction is the gain of electrons.

Reduction with carbon

Process used to extract metals from their oxides when the metal is less reactive than carbon. The metal oxide is heated with carbon so that carbon reduces the metal oxide to the metallic element.

Reversible reaction

A reaction in which the products can react together to reform the reactants. Reversible reactions are denoted by the symbol ⇌.