Chemistry Definitions

The minimum energy that a particle needs in order to react; the energy (enthalpy) difference between the reactants and the transition state.

An organic compound with the general formula

O

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R-C-H (RCHO)

The metals in group 2 of the periodic table.

a hydrocarbon with C-C and C-H single bonds only, with the general formula CnH2n+2

a hydrocarbon with C=C, C-C and C-H, with the general formula CnH2n

pure elements which can exist in different physical forms in which their atoms are arranged differently. e.g. diamond, graphite, buckmisterfullerene are allotropes of carbon

% atom economy = mass of desired product / total mass of reactants x 100

a region of space around an atomic nucleus where there is a high probability of finding an electron

the number of particles in a mole of substance

6.022x1023

the enthalpy change required to break a covalent bond with all species in the gaseous state

an instrument for measuring the heat changes that accompany chemical reactions

a substance that alters the rate of a chemical reaction but is not used up in the reaction

the breaking, with the aid of a catalyst, of long chain alkane molecules, into shorter chain hydrocarbons

an organic ion in which one of the carbon atoms has a positive charge

a processes, in which as much carbon dioxide is absorbed from the air as it is given out

the starting materials in an industrial chemical process

covalent bonding in which both electrons in the bond come from one atom in the bond

describes a chemical bond in a pair of electrons are shared between the two atoms

covalent bonding in which both electrons in the bond come from one atom in the bond.

describes electrons that are spread over several atoms and help to bond them together

an intermolecular force that the results from the attraction between molecules with permanent dipoles

a chemical reaction in which one atom or group of atoms replaces another in a compound e.g. Zn + CuO →ZnO + Cu

the formula of a compound drawn out so that each atom and each bond is shown

H H H

/ / /

H-C-C-C-H

/ / /

H H H

describes a redox reaction in which the oxidation number of some atoms of a particular element increase and that of other atoms of the same element decreases

a situation in which the composition of a constant concentration reaction mixture does not change because both forward and backward reactions are proceeding at the same rate

the probability of electrons being found in a particular volume of space

a theory which explains the shapes of simple molecules by assuming that pairs of electrons around a central atom repel each other and thus take up positions as far away as possible from each other in space

the power of an atom to attract the electrons in a covalent bond

an electron-deficient atom, ion or molecule that takes part in an organic reaction by attacking areas of high electron density in another reactant

a reaction in which a carbon-carbon double bond is saturated, by the carbon-carbon double bond attacking an electrophile

the forces of attraction and repulsion between electrically charged particles

a reaction in which an atom or group of atoms is removed from a reactant

the simplest whole number ratio of atoms of each element in a compound

describes a reaction in which heat is taken in as reactants change to products; the temperature thus drops

a measure of heat energy given out or taken in when a chemical or physical change occurs at constant pressure

diagrams in which the enthalpies of the recants and products of a chemical reaction are plotted on a vertical scale to show their relative levels

the mixtures of reactants and products formed when a reversible reaction is allowed to proceed in a closed container until no further change occurs. the forward and backward reactions are still proceeding but at the same rate

describes a reaction in which heat is given out as the reactants change to products; the temperature thus rises

the area of an infra-red spectrum below about 1500cm-1. It is caused by complex vibration of the whole molecule and is characteristics of a particle molecule

a mixture of hydrocarbons collected over a particular range of boiling points during the fractional distillation of crude oil

a chemical species with an unpaired electron - usually highly reactive

an atom or group if atoms in an organic molecules which is responsible for the characteristics reactions of that molecule

a vertical column of elements in the periodic table. the element have similar properties because they have the same outer electron arrangement

an equation for a redox reaction which considers just one of the species involved and shows explicitly the electron transferred to or from it

a set or organic compounds with the same functional group. the compounds differ in the length if their hydrocarbon chains

a type of intermolecular force in which a hydrogen atom (Hδ+) interacts with a more electronegative atom with a δ- charge

a combustion reaction in which there is insufficient oxygen for all the carbon in the fuel to burn to carbon dioxide. carbon monoxide and/or carbon (soot) are formed

describes a chemical bond in which an electron or electrons are transferred from one atom to another, resulting in the formation of oppositely charged ions with electrostatic forces of attraction between them.

the energy required to remove a mole of electrons from a mole of isolated gaseous atoms or ions

one or two (or more) compounds with the same molecular formula but different arrangement of atoms in space.

an organic compound with the general formula R2CO in which there us a C=O double bond

O

//

R - C - R

a regular three-dimensional arrangement of atoms, ions or molecules

in an organic substitution reaction, the leaving group is an atom or group of atoms that is ejected from the starting material, normally taking with it an electron pair and forming a negative ion

a pair of electrons in the outer shell of an atom that is not involved in bonding

the distribution of energies (and therefore speeds) of the molecules in a gas or liquid

the average value of the bond dissociation enthalpy for a given type of bond taken from a range of different compounds

describes a chemical bond in which outer electrons are delocalised within the lattice of metal ions

a quantity of a substance that contains 6.022 x 10-23 of particles

a formula that tells us the actual numbers of atoms of each different element that make up a molecule of a compound

in mass spectrometry this is a molecule of the sample which has been ionized but which has not broken up during its flight through the instrument

a small molecular that combines with many other monomers to form a polymer

protons and neutrons - the sub-atomic particles found in a nuclei of atoms

an ion or group of atoms with a negative charge or partially negatively charged area that takes part in an organic reaction by attacking an electron-deficient area in anther reactant

an organic reaction in which a molecule with a partially positively charged carbon atom is attacked by a reagent with a negative charge or partially negatively charged are (a nucleophile), it results in the replacement of one if the groups or atoms on the original molecules by the nucleophile

the tiny, positively charged center of at atom compound of protons and neutrons

a reaction in which an atom or group of atoms loses electrons

the number of electrons lost or gained by an atom in a compound compared to the uncombined atom. it forms the basis of a way of keeping track of redox (electron transfer) reactions. also called oxidation number

a reagent that oxidises (removes electrons from) another species

in a chemical reaction this is the actual amount of product produced divided by the theoretical amount, expressed as a percentage

a horizontal row of elements in the periodic table. there are trends in the properties of the elements as we cross a period

the regular recurrence of the properties of elements when they are arranged in the atomic number order as in the periodic table

describes a molecule in which the charge in not symmetrically distributed so that one area is slightly positively charged and another slightly negative charged

describes the tendency of some atoms to release electrons via a covalent

the number of protons in the nucleus of an atom; the same as the atomic number

short for the reduction-oxidation reaction, it describes reactions in which electrons are transferred from one species to another

a reagent that reduces another species

a reaction in which an atom or group of atoms gain electrons

average mass of an atom divided by 1/12 mass of 1 carbon 12 atom

average mass of an entity divided by 1/12 mass of 1 carbon 12 atom

average mass of an molecule divided by 1/12 mass of 1 carbon 12 atom

a compound containing only hydrogen and carbon with only C-C and C-H single bonds, i.e. one to which no more hydrogen can be added

the amount of heat needed to raise the temperature of 1g of substance by 1k

ions that are unchanged during a chemical reaction, that is, they take no part in the reaction

the enthalpy change when 1 mole of a substance is completely burned in oxygen with all reactants and products in their standard states (298k and 100kPa)

the enthalpy change when 1 mole of a substance is formed from its elements with all reactants and products in their standard states (298k and 100kPa)

isomers with the same molecular formula and the same structure, but a different position of atoms in space

describes the simple whole number ratios in which chemical species react

the force that holds the protons and neutrons together within the nucleus of the atom

a way of writing the formula of an organic compound in which bonds are not shown but each carbon atom is written separately with the atom or groups of atoms attached to it

a sequence of chemical reactions (with their enthalpy changes) that convert a reactant into a product, the total enthalpy change of the sequence of reactions will be the conversion of the reactant to the product directly (or by any other route)

a type of inter-molecular force of attraction that is caused by instantaneous dipoles and acts between all atoms and molecules