IGCSE - Chemistry

Diffusion

the spreading of one substance through another from a region of high concentration to a region of low concentration due to the continuous random motion of particles.

Atom

the smallest part of an element that can exist as a stable entity

Ion

a species with a positive or negative charge

Element

a substance that cannot be split up by chemical means

Compound

a pure substance, which contains two or more different elements chemically bonded together

Molecule

the smallest part of an element or compound, which can exist alone under ordinary conditions.

Mixture

two or more substances that can be separated by physical means

Proton (atomic) number

the number of protons in the nucleus of an atom

Mass (nucleon) number

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

Isotopes

atoms of the same element with the same number of protons but different number of neutrons

Ionic bond

a strong electrostatic attraction between oppositely charged ions

Ionic lattice

a giant structure of ionic compounds with a regular arrangement of alternating positive and negative ions.

Covalent bond

formed when a pair of electrons is share between atoms leading to noble gas configurations.

Macromolecule

consists of a large number of atoms bonded together to form one molecule with a very high relative molecular mass

Allotropes

different crystalline forms of the same element with the same chemical properties but different physical properties.

Metallic bonding

an electrostatic attraction between positive ions in a giant metallic lattice and a sea of delocalised electrons.

Molecular formula

the number and type of different atoms in one molecule

Empirical formula

the simplest whole number ratio of the different elements or ions in a compound

Relative molecular mass, Mr

the sum of relative atomic masses

Mole

the unit of amount of a substance.

Avogadro’s constant

6.02 x 10^23

Electrolysis

the breakdown of an ionic compound when in molten or aqueous state, using an electric current

Anode

the positive electrode

Cathode

the negative electrode

Electrolyte

a molten or aqueous substance that undergoes electrolysis

Hydrogen-oxygen fuel cells

use hydrogen and oxygen to produce electricity with water as the only chemical product.

Exothermic reaction

transfers thermal energy to the surroundings leading to an increase in temperature of the surroundings

Endothermic reaction

takes in thermal energy from the surroundings leading to a decrease in temperature of the surroundings

Enthalphy change, ΔH

the transfer of thermal energy during a reaction

Activation Energy, Ea

the minimum energy that colliding particles muct have to react.

Catalyst

a substance that increases the rate of a reaction by decreasing the activation energy and is unchanged at the end of the reaction.

Redox reaction

a reaction involving simultaneous oxidation and reduction

Oxidation

the loss of electrons or an increase in oxidation number

Reduction

the gain of electrons or decrease in oxidation number

Oxidising agents (oxidant)

a substance that oxidises another substance and is itself reduced

Reducing agent (reductant)

a substance that reduces another substance and is itself oxidised

Acid

a proton donor

Strong acid

an acid that completely dissociates/ionises in aqueous solution

Weak acid

an acid that partly dissociates/ionises in aqueous solution

Base

a proton acceptor

Alkali

soluble bases

Amphoteric oxides

oxides that react with acids and with bases to produce a salt and water

Hydrated substance

a substance that is chemically combined with water

Anhydrous substance

a substance containing no water

Water of crystallisation

the water molecules present in hydrated crystals

Alloy

a mixture of a metal with other elements

Functional group

the atom, or group of atoms, that determine the chemical properties of a homologous series

Structural formula

an unambiguous description of the way the atoms in a molecules are arranged

Homologous series

a family of similar compounds with similar chemical properties due to the presence of the same functional group

Structural isomers

compounds with the same molecular formula, but different structural formula.

Saturated compounds

molecules in which all C-C bonds are single bonds

Unsaturated compounds

molecules in which one or more of the carbon-carbon bonds are not single bonds.

Hydrocarbons

compounds made from hydrogen and carbon only

Petroleum

a mixture of hydrocarbons

Solvent

a substance that dissolves a solute

Solute

a substance that is dissolved in a solvent

Solution

a mixture of one or more solutes dissolved in a solvent

Saturated solution

a solution containing the maximum concentration of a solute dissolved in a solvent at a specific temperature

Residue

a substance that remains after evaporation, distillation, filtration or any similar process

Filtrate

a liquid or solution that has passes through a filter

Precipitate

forms when two solutions are mixed/reacted together

Rf Value

distance travelled by sample/ distance travelled by solvent front