Definitions for the 'C2: Elements, Compounds and Mixtures' topic of the GCSE OCR Gateway Spec.
Fully detailed, easy to understand & perfect definitions for use in the exams.
Alloys- a metal compound made by combining two or more metals together. This process is
carried out to give greater strength or resistance to corrosion.
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.
Covalent bond- a shared pair of electrons between two non-metals.
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.
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 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.
Evaporation:- a separation technique to separate soluble solids from solutions. The solution
is slowly heated in an evaporating dish so that the solvent evaporates to leave the dry
crystals.
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.
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.
Gas chromatography- a technique used to separate a mixture of volatile liquids. A tube is
packed with a solid or a solid coated in a liquid (stationary phase) and a gas (mobile phase)
is passed through the column under pressure at high temperature. Each component takes a
different time to pass through the tube. This is called the retention time which can be used
to identify the component.
Giant covalent structure- a molecular structure containing many atoms covalently bonded
together. The strong covalent bonds mean that giant covalent structures have high melting
points.
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, forming 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.
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.
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