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Chemistry
A2 Chemistry
| Term | Definition |
|---|---|
| Acid dissociation constant, K(a) | The acid dissociation constant of an acid HA is defined at K(a)=[H+(aq)][A-(aq)]/[HA(aq)]. |
| Activation energy | The minimum energy required to start a reaction by breaking bonds in the reactants. |
| Addition polymer | A very long molecular chain formed by repeated addition reactions of many unsaturated alkene molecules (monomers). |
| Addition reaction | A reaction in which a reactant is added to an unsaturated molecule to make a saturated molecule. |
| Aliphatic hydrocarbon | A hydrocarbon where carbon atoms are joined together in straight or branched chains. |
| Alkali | A base that dissolves in water forming OH-(aq) ions. |
| Alkanes | The homologous series with the general formula C(n)H(2n+2). |
| Alkylammonium salt | A compound where the hydrogen(s) on an ammonium ion have been substituted by alkyl chains. |
| Alkylation | Addition of hydrocarbon chains to an organic compound. |
| Alkyl group | An alkane with a hydrogen atom removed, e.g. CH3, C2H5; often shown as 'R' |
| Amide | A class of compound with a functional group made of an acyl group, which is directly attached to an amine. |
| Amount of substance | The quantity whose unit is the mole. Chemists use "amount of substance" as a means of counting atoms. |
| Amphoteric chemicals | Chemicals that can react with both acids and bases. |
| Anion | A negatively charged ion. |
| Anhydrous | A substance that contains no water molecules. |
| Arrhenius plot | A graph of In k =In A - Ea/R x 1/T where In K is plotted against 1/T |
| Atomic orbital | A region of space where it is likely that you will find electrons. Each orbital can hold up to two electrons, with opposite spins. |
| Atomic (proton) number | The number of protons in the nucleus of an atom. |
| Average bond enthalpy | The mean energy needed for 1 mole of a given type of gaseous bonds to undergo homolytic fission. |
| Avogadro constant | The number of atoms per mole of the carbon-12 isotope (6.02 x 10(23) mol(-1). |
| Base | A chemical that will react with an acid. |
| Benzene | A naturally occurring aromatic compound, which is a very stable planar ring structure with delocalised electrons. |
| Benzene derivative | A benzene ring that has undergone a substitution reaction. |
| Boltzmann distribution | The distribution of energies of molecules at a particular temperature, often shown as a graph. |
| Bronsted-Lowry acid | A proton, H+, donor. |
| Bronsted-Lowry base | A proton, H+, acceptor. |
| Buffer solution | A mixture that minimises pH changes on addition of small amounts of acid or base. The word "minimises" is essential to this definition. |
| Carbocation | An organic ion in which a carbon atom has a positive charge. |
| Catalyst | A substance that increases the rate of a reaction without being used up in the process. |
| Cation | A positively charged ion. |
| Chemical shift | The scale that compares the frequency of NMR absorption with the frequency of the reference peak of TMS. |
| Chiral carbon | A chiral carbon has four different groups attached to it. |
| Chromatogram | A visible record showing the result of separation of the components of a mixture by chromatography. |
| Cis-trans isomerism | A type of E/Z isomerism where each carbon of the C=C double bond caries the same atom or group. |
| Complex ion | A transition metal ion bonded to one or more ligands by coordination bonds (dative covalent bonds). |
| Condensation polymerisation | The chemical reaction to form a long-chain molecule by elimination of a small molecule, such as water. |
| Conjugate acid-base pair | Two species that transform into each other by gain or loss of a proton. |
| Coordination number | The total number of coordinate bonds formed between a central metal ion and its ligands. |
| Covalent bond | A bond formed by a shared pair of electrons between nuclei. |
| Curly arrow | A symbol used in reaction mechanisms to show the movement of an electron pair. |
| Dative covalent bond | A bond formed by a shared pair of electrons that has been provided by one of the bonding atoms only. Also known as a coordinate bond. |
| Degradable polymer | A polymer that breaks down into smaller fragments when exposed to light, heat or moisture. |
| Delocalised electrons | Electrons that are shared between more than two atoms. |
| Deuterium | An isotope of hydrogen and does not produce a signal in the proton NMR spectrum. |
| Directing effect | How a functional group attached directly to an aromatic ring affects which atoms are more likely to undergo substitution. |
| Displayed formula | A formula which shows the relative positions of atoms and the bonds between them. |
| Disproportionation | The oxidation and reduction of the same element in a redox reaction. |
| Distillation | A technique used to separate miscible liquids or solutions. |
| Dynamic equilibrium | The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and all the chemicals have their concentrations maintained. |
| Electron structure or configuration | The arrangement of electrons in an atom or ion. |
| Electrophile | An electron-pair acceptor. |
| Electrophilic substitution | A substitution reaction where an electrophile is attracted to an electron-rich atom or part on a molecule and a new covalent bond is formed by the electrophile accepting an electron pair. |
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Lauren31158
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