OCR F322 Chemistry definitions
· Alkanes – saturated hydrocarbons that contain only C-C single bonds.
· Hydrocarbons – molecules containing ONLY carbon and hydrogen.
· Systematic nomenclature – the naming of an organic molecule.
· Molecular formula – actual no. of each atom in a molecule.
· Empirical formula – simplest ratio of a formula.
· Structural isomers – molecules with same molecular formula but different structural formula.
· Homologous series – group of molecules with the same general formula but have a molecular formula that differs by CH₂.
· Sigma-bonds – bonds that exist between C-C single bonds that can rotate. It is formed by the overlap of s-orbitals.
· Tetrahedral – the shape of an alkane with a 109.5° bond angle.
· VDW forces – the intermolecular forces that exist between alkane molecules. The larger the alkane molecule, the more electrons so the greater the VDW forces and the higher the boiling point. Branched isomers have a lower boiling point because of a lower surface contact between molecules so lower VDW forces.
· Fractional distillation – the separation of hydrocarbons into fractions based on their boiling point.
· Cracking – the process of heating longer alkanes with a catalyst to break them into smaller molecules, usually of which are an alkane and an alkene.
· Reforming – the process of converting a straight chain alkane into a cyclic alkane or arene and releasing hydrogen.
· Isomerisation – the process of changing a straight chained alkane into a branched structural isomer.
· Substitution reaction – a reaction where an atom of one molecule is swapped for an atom of another molecule.
· Photochemical reaction – a reaction requiring light.
· Mechanism – a sequence of steps which show how the reactants become the products.
· Photo-dissociation – the breaking of a bond due to light.
· Free radical – a species with an unpaired electron.
· Homolytic fission – the breaking of a bond to give 2 free radicals.
· Alkenes – unsaturated hydrocarbons with C=C bond.
· Pi-bond – the weaker bond of the C=C double bond relative to the sigma bond. It is formed by the overlap of p-orbitals.
· C=C bond – a double bond that has a pi bond and a sigma bond. It is an area of high e- density so is very reactive. It cannot rotate.
· Functional groups – the atom or group of atoms in a molecule responsible for its chemical properties.
· Stereoisomers – molecules with the same molecular and structural formula but a different arrangement in space. For example, E/Z or cis/trans isomerism.
· E/Z – a type of isomerism that occurs when a molecule has a C=C bond and each carbon on the C=C bond has two different groups.