OCR Chemistry A Level definitions
Terms in this set (134)
A substance that releases hydrogen ions (H+) in aqueous solution (proton donor).
The minimum amount of kinetic energy that particles need to have in order to react when they collide.
A long-chain molecule made by lots of small alkene molecules adding together.
A substance with the general formula CnH2n+1OH.
A substance with the general formula CnH2nO which has a hydrogen and one alkyl group attached to the carbonyl carbon atom.
An organic compound that contains carbon and hydrogen joined together in a non-aromatic ring.
An organic compound that contains carbon and hydrogen joined together in a straight chain, branched chains or non-aromatic rings.
A base that is soluble in water and releases hydroxide ions (OH-) in aqueous solution.
A hydrocarbon with the general formula CnH2n+2.
A hydrocarbon with the general formula CnH2n and containing at least one carbon-carbon double bond.
A hydrocarbon fragment with the general formula CnH2n+1.
A salt that doesn't contain any water of crystallisation.
An organic compound that contains a benzene ring.
The proportion of reactant atoms that become part of the desired product, expressed as a percentage.
The energy needed to break one mole of covalent bonds in the gas phase (averaged over the different compounds that the bond is found in)
A proton acceptor.
A model for the structure of an atom proposed by Niels Bohr. He suggested that electrons only one exist in fixed orbitals and not anywhere else.
A theoretical model that describes the distribution of kinetic energies of molecules in a gas.
An organic ion containing a positively charge carbon atom.
An organic compound that contains a carbon-oxygen double bond.
A substance which has a COOH group attached to the end of a carbon chain.
A substance that increases the rate of a reaction by providing an alternative reaction pathway with a lower activation energy. The catalyst is chemically unchanged at the end of the reaction.
A molecule that contains the same atoms as another molecule but has a different arrangement of carbon skeleton.
The amount of charge in relation to the size of the ion.
A haloalkane containing fluorine and chlorine and no hydrogen. CFCs contribute to the ozone depletion.
A special type of E/Z isomerism where two of the attached groups to the carbon atoms around the C=C double bond are the same.
The theory that a reaction will not take place between two particles unless they collide in the right direction and with at least a certain minimum amount of energy.
During a substance completely in excess oxygen. Complete combustion of a hydrocarbon will produce carbon dioxide and oxygen only.
Coordinate (dative covalent) bond
A covalent bond formed when one atom provides both of the shared electrons.
The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.
A type of alkane which has one or more non-aromatic carbon rings.
A reaction in which water is eliminated from an organic molecule.
A difference in charge between two atoms caused by an unequal spread of the electron density in a bond.
A redox reaction where a more reactive element gains electrons from a less reactive element in an ionic solution.
A way of representing a molecule that shows how all of the atoms are arranged and all the bonds between them.
When an element is simultaneously oxidised and reduced in a single chemical reaction.
A technique used to separate liquids with different boiling points. A mixture is gently heated so that substances evaporate and can be collected in order of increasing boiling point.
In a reversible reaction, this is reached when the concentrations of reactants and products are constant, and the forward reaction and the backwards reaction are going at the same rate.
A type of stereoisomerism that is caused by the restricted rotation about the carbon-carbon double bond. Each of the carbon atoms must be attached to two different groups.
A subatomic particle with a relative charge of -1 and a relative mass of 1/2000, location in orbitals around the nucleus.
Electron shell repulsion theory
The theory that in a molecule lone pair/lone pair bond angles are the biggest, lone pair/bonding pair bond angles are the second biggest and bonding pair/bonding pair angles are the smallest.
The ability of an atom to attract the bonding electrons in a covalent bond.
An electron-pair acceptor.
A reaction mechanism where a double bond in an alkene opens up and atoms are added to the carbon atoms.
A reaction in which a pair of atoms or groups of atoms are removed from an organic molecule.
A formula giving the simplest whole number ratio of atoms of each element in a compound.
A reaction that absorbs energy in the form of heat (∆H is positive).
The heat energy transferred in a reaction at a constant pressure (∆H).
Enthalpy profile diagram
A graph showing how enthalpy changes during a chemical reaction.
Equilibrium constant, Kc
A ratio worked out from the concentration of the products and reactants once a reversible reaction has reached equilibrium.
A reaction that gives out energy in the form of heat (∆H is negative).
First ionisation energy
The energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms of an element.
The group of atoms that is responsible for the characteristic reactions of a molecule (e.g. -OH for alcohols, -COOH for carboxylic acids, C=C for alkenes).
Functional group isomer
A molecule that has the same molecular formula as another molecule, but with the atoms arranged into different functional groups.
An algebraic formula that can describe any member of a homologous series of compounds.
Giant covalent lattice
A structure consisting of a huge network of covalently bonded atoms. Also called a macromolecular structure.
Giant ionic lattice
A regular repeated structure made up of oppositely charged ions strongly attracted to each other in all directions.
Giant metallic lattice.
A regular structure consisting of closely packed positive metal ions surrounded by a sea of delocalised electrons.
A negative ion of a halogen.
An alkane with at east one halogen atom in place of a hydrogen atom.
The total enthalpy change of a reaction is independent of the route via which the reaction proceeds.
A catalyst which is in a different physical state from the reactants of the reaction it is catalysing.
When a covalent bond breaks unevenly, with one of the bonding atoms receiving both of the electrons from the bonded pair, resulting in the formation of positively charged cation and a negatively charged anion.
A catalyst which is in the same physical state as the reactants of the reaction it is catalysing.
A family of organic compounds that have the same general formula and similar chemical properties.
When a covalent bond breaks evenly, with each of the bonding atoms receiving one electron from the bonded pair, resulting in the formation of two electrically uncharged radicals.
A salt that contains water of crystallisation.
A molecule that only contains carbon and hydrogen atoms.
The strongest intermolecular force. It occurs when polarised covalent bonds contain hydrogen atoms to form weak bond with lone pairs of electrons on the fluorine, nitrogen and oxygen atoms of other molecules.
A reaction where molecules are split apart by water molecules. The water molecules are also split into hydrogen ions (H+) and hydroxide ions (OH-).
Burning a substance in a poor supply of oxygen. Incomplete combustion of a hydrocarbon produces carbon monoxide, water and sometimes carbon and carbon dioxide.
A substance that changes colour at a certain pH.
Induced dipole-dipole interactions
A type of intermolecular force caused by temporary dipoles, which causes all atoms and molecules to be attracted to each other. Also called London (dispersion) forces.
Infrared (IR) spectroscopy
An analytical technique used to identify the functional group present in a molecule, by measuring the infrared absorption frequencies of its bonds.
An electrostatic attraction between oppositely charged ions.
One of two or more forms of an element with the same number of protons but different numbers of neutrons.
A substance with the general formula CnH2nO which has two alkyl groups attached to the carbonyl carbon atom.
A regular structure made up of atoms or ions.
Le Chatelier's principle
If there's a change in concentration, pressure or temperature, the equilibrium will shift to help counteract the change.
An analytical technique used to find the structure of molecule by measuring the masses of the ions it produces when it's bombarded with electrons.
A number (6 x 10^23 = Avogadro constant) used to quantify amounts of particles.
A way of representing molecules that shows the actual number of atoms of each element in a molecule.
A small molecule which is used to make a polymer.
A reaction between an acid and a base to produce a salt and water.
An electron-pair donor.
Nucleophilic substitution reaction
A reaction where a nucleophile attacks a polar molecule (at the more electropositive position) and replaces a functional group in that molecule.
A region of a sub-shell that can contain a maximum of 2 electrons with opposite spins.
Loss of electrons/gain of oxygen/loss of hydrogen.
The formal charge on an atom in a species if it were ionic. Can also be described as the number of electrons of that atom involved in bonding.
Something that accepts electrons and gets reduced.
The amount of product that is actually obtained during a reaction expressed as a percentage of the amount of product that should form.
The trends in physical and chemical properties of elements as you go across the periodic table.
Permanent dipole-dipole interactions
Intermolecular forces that exist because the difference in electronegativities in a polar bond causes weak electrostatic forces of attraction between molecules.
Pi (π-) bond
A type of bond formed when two p orbitals overlap sideways.
A covalent bond where a difference in electronegativity has caused an unequalspread of the electron density in the bond.
A molecule containing polar bonds that are arranged so the dipoles don't cancel each other out, causing an overall dipole to be formed.
A long molecule formed from lots of smaller molecules joined together.
A molecule with the same molecular formula as another molecule but with the functional group in a different position.
A particle with an unpaired electron, written like this Cl•.
The change in the amount of reactants or products per unit time.
A reaction where reduction and oxidation happen simultaneously.
Something that donates electrons and gets oxidised.
Gain of electrons/loss of oxygen/gain of hydrogen.
Heating a reaction mixture in such a way that you boil it without losing volatile solvents, reactants or products. Any vaporised compounds cool, condense and drip back into the reaction mixture.
Relative atomic mass
The average mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12.
Relative isotopic mass
The mass of an atom of an isotope of an element compared to 1/12 of the mass of an atom of carbon-12.
A compound formed when the hydrogen in an acid molecule is replaced by a metal ion or ammonium ion.
Where all the carbon-carbon bonds in a hydrocarbon are single bonds.
Sigma (σ-) bond
A type of bond formed when two orbitals overlap directly between the bonded atoms.
A simplified organic formula which only shows the carbon skeleton and its associated functional groups.
100kPa (about 1 atm) pressure, a temperature of 298K and 1 mol/dm3 solutions.
Standard enthalpy change of combustion
The enthalpy change when 1 mole of a substance is completely burned in oxygen under standard conditions with all reactants and products in their standard states (∆cHØ).
Standard enthalpy change of formation
The enthalpy change when 1 mole of a compound is formed from its elements in their standard states under standard conditions (∆fHØ).
Standard enthalpy change of neutralisation
The enthalpy change when an acid and an alkali react together to form 1 mole of water, under standard conditions (∆neutHØ).
A molecule that has the same structural formula as another molecule but the atoms are arranged differently in space.
An acid/base that completely ionises in an aqueous solution.
A way of representing molecules that shows the atoms carbon by carbon, with the attached hydrogens and functional groups.
A molecule with the same molecular formula as another molecule, but with the atoms connected in a different way.
A sub-division of an energy level - s, p, d or f.
A reaction where some atoms from one reactant are swapped with atoms from another reactant.
Successive ionisation energy
The energy needed to remove 1 mole of each subsequent electron from each ion in 1 mole of positively charged gaseous ions.
Where a hydrocarbon has one or more multiple carbon-carbon bonds.
A substance's tendency to evaporate (turn into a gas).
Water of crystallisation
The water contained in an ionic lattice.
An acid/base that only partially ionises in an aqueous solution.
A system that minimises pH changes on the addition of small amounts of an acid or base.
conjugate acid/base pair
Two species that interconverted by loss/gain of a proton (H+ ion).
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard conditions.
A molecule or ion that can donate a pair of electrons to the transition metal ion.
standard enthalpy change of hydration
The enthalpy change that accompanies the dissolving of gaseous ions in water to form one mole of aqueous ions.
standard enthalpy of solution
The enthalpy change involved when one mole of a solid ionic lattice is dissolved in water.
The point in a titration at which the volume of one solution has reacted exactly with the volume of the second solution, e.g. neutralisation point.
The point in a titration when the indicator change colour.
standard electrode potential
The e.m.f of a half cell compared with a standard hydrogen half cell, measured at 298K, 100kPa pressure and solution concentrations of 1 mol/dm3.