All keywords

Acid

A species that releases H+ ions in aqueous solution

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Activation Energy (E_a)

The minimum energy required to start a reaction by the breaking of bonds

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Actual Yield

The amount of product obtained from a reaction

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Addition polymerisation

Formation of very long molecular chain (addition polymer) by repeated addition reactions of many unsaturated alkene molecules (monomers)

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Addition reaction

A reaction in which a reactant is added to an unsaturated molecule to make an unsaturated one

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Adsorption

The process that occurs when a gas, liquid or solute is held to the surface of a solid

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Alicyclic

Containing carbon atoms joined together in a ring that is not aromatic

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Aliphatic

Containing carbon atoms joined together in unbranched (straight) or branched chains

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Alkali

A type of base that dissolves in water to release hydroxide ions [OH-(aq)]

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Alkanes

The hydrocarbon homologous series with the general formula of (C_nH_2n+1)

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Alkenes

The hydrocarbon homologous series with one double carbon to carbon bond and the general formula C_nH_2n

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Alkyl group

A side chain formed by removing a hydrogen atom from the alkane parent. Often shown by the letter R

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Alkynes

The hydrocarbon with one triple carbon to carbon bond and the general formula C_nH_2n-2

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Amount of substance

The quantity whose unit of the mole. Chemists use amount of substance as means of countring atoms

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Anhydrous

Containing no water molecules

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Anion

A negatively charged ion with more electrons than protons

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Aromatic

Containing one or more benzene rings

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Atom economy

Sum of molar masses of desired products divided by the sum of molar mass of all products multiplied by 100

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Atomic number (z)

The number of protons in the nucleus of an atom (also known as proton number)

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Atomic orbital

A region around the nucleus that can hold up to two electrons with opposite spins

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Average bond enthalpy

The average enthalpy change that takes place when breaking by homolytic fission one mole of a given bond in the molecules of a gaseous species

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Avogadro's constant

6.02 x 10^23 mol^-1 (the number of atoms per mole of carbon 12)

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Avogadro's hypothesis

Equal volumes of gases at the same temperature and pressure contain the same number of molecules

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Base

A compound that neutralises an acid to form a salt

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Binary compound

A compound containing two elements only

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Bond angle

The angle between two bonds at an atom

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Bonded pair

A pair of electrons shared between two atoms to make a covalent bond

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Carbocation

An ion that contains a positively charged carbon atom

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Catalyst

A substance that increases the rate of reaction and doesn's get used up in the process. A catalyst provides an alternative route for the reaction with a lower activation energy

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Cation

A positively charged ion with fewer electrons that protons

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Chain reaction

A reaction in which the propagation steps release new radicals that continue the reaction

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Cis-trans isomerism

Special type of E/Z isomerism in which two hydrogen atoms around the C-C double bond. The cis isomer (Z) has hydrogen atoms on each carbon on the same side whilst trans isomer (E) has them on different sides of the double bond

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Closed system

A system isolated from its surroundings

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Collision theory

Two particles reacting musy collide for a reaction to occur, must be in the correct orientation and have sufficient energy to overcome the activation energy of the reaction

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Coordinate bond

A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only. Also referred to as dative covalent bond

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Covalent bonding

The strong electrostatic attraction between a shared pair of electrons and nuclei of the bonded atoms

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Dative covalent bond

A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only. Also referred to as a coordinate bond

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Dehydration

An elimination reaction in which water is removed from a saturated molecule to make an unsaturated one

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Delocalised electron

Electrons that are shared between more than two atoms

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Desorption

Release of an adsorbed substance from a surface

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Dipole

A separation in electrical charge so that one atom of a polar covalent bond or one end of a polar molecule has a small positive charge δ+ and the other a small negative charge δ-

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Dipole-dipole force

An attractive force between permanent dipoles in neighbouring polar molecules

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Displacement reaction

A reaction in which a more reactive element displaces a less reactive element from an aqueous solution of its ions

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Displayed formula

A formula that shows the relative positioning of atoms in a molecule and all the bonds between them

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Disproportionation

A redox reaction in which the element is both reduced and oxidised

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Dynamic equilibrium

The equilibrium that exists in a closed system where the rate of the forward reaction is the same as that of the reverse reaction and the concentrations do not change.

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E/Z isomerism

A type of stereoisomerism in which different groups attached to each carbon of a C-C double bond may be arranged differently in space because of the restricted rotation around the double bond

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Electron configuration

A shorthand method for showing how electrons occupy sub shells in an atom

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Electronegativity

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

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Electrophile

An atom or group of atoms that are attracted to an electron rich region where they accept a pair of electrons

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Electrophilic addition

An addition reaction in which the first step is attack by an eletrophile on a region of high electron density

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Elimination reaction

The removal of a molecule from a saturated molecule to make an unsaturated one

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Empirical formula

A formula that shows the simplest whole number ratio of atoms of each element present in a compound

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End point

The point in a titration where the indicator changes colour suggesting that the reaction is complete

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Endothermic reaction

A reaction in which the enthalpy of the products is greater than that of the reactants resulting in heat being taken in from the surroundings (ΔH is positive)

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Enthalpy

The heat content that is stored in a chemical system

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Enthalpy change (ΔH)

Difference in enthalpy between reactants and products in a reaction

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Enthalpy cycle

A diagram showing alternative routes between reactants and products which allows the indirect determination of an enthalpy change from other known enthalpy changes using Hess's law

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Equilibrium constant K_c

A measure of the position of the equilibrium. the magnitude of the equilibrium constant indicates whether there are more reactants or more products in an equilibrium system

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Exothermic reaction

A reaction in which the enthalpy of the products is smaller than the enthalpy of the reactants resulting in heat loss to the surroundings (ΔH is negative)

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Fingerprint region

An area of infrared spectrum below 1500cm^-1 that gives a characteristic pattern for different compounds

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First ionisation energy

The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions

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Fractional distillation

The separation of components in a liquid mixture by their different boiling points into fractions with different compositions

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Fragment ions

Ions formed from the break down of the molecular ion in a mass spectrometer

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Fragmentation

The process in mass spectrometry that causes a positive ion to split into smaller pieces one of which is a positive fragment ion

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Functional group

The part of the organic molecule responsible for its chemical reactions

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General formula

The simplest algebraic formula of a member of a homologous series. For example the general formula of alkanes is C_nH_2n+2

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Giant covalent lattice

A three dimensional structure of atoms bonded together by strong covalent bonds

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Giant ionic lattice

A three dimensional structure of oppositely charged ions bonded together by strong ionic bonds

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Giant metallic lattice

A three dimensional structure of positive ions and delocalised electrons bonded together by strong metallic bonds

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Group

Vertical column in the periodic table. Elements in a group have similar chemical properties and their atoms have the same number of outer shell electrons

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Hess' Law

If a reaction can take place by more than one route and the initial and final conditions are the same, the total enthalpy change is the same for each route

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Heterogeneous catalysis

A reaction in which the catalyst has a different physical state from the reactants; frequently reactants are gases while the catalyst is a solid

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Heterolytic fission

The breaking of covalent bond with both of the bonded electrons going to one atom forming a cation and anion

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Homogeneous catalysis

A reaction in which the catalyst and the reactants are in the same physical state, which is most frequently the aqueous or gaseous state

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Homologous series

A series of organic compounds with the same functional group but with each successive member differing by CH_2

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Homolytic fission

The breaking of a covalent bond with one of the bonded electrons going to each atom, forming two radicals

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Hydrated

A crystalline compound containing water molecules

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Hydrocarbon

A compound containing carbon and hydrogen only

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Hydrogen bond

A strong dipole-dipole attraction between an electron defficient hydrogen atom of -NH, -OH or HF on one molecule and a lone pair of electrons on a highly electronegative atom containing N, O or F on a different molecule

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Hydrolysis

A reaction with water that breaks a chemical compound into two compounds, the H and OH in a water molecule becomes incorporated into the two compounds

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Induced dipole-dipole interaction

Attractive forces between induced dipoles in different molecules; also called London forces

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Initiation

The first stage in a radical reaction in which radicals start when a covalent bond is broken by homolytic fission of a covalent bond

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Intermediate

A species formed during a reaction that reacts further and is not present in the final products

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Intermolecular forces

An attractive force between molecules. Intermolecular forces can be London forces, permanent dipole dipole interaction and hydrogen bonding

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Ion

A positively or negatively charged atom or a (covalently bonded) group of atoms (a polyatomic ion) where the number of electrons is different from the number of protons

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Ionic bonding

The electrostatic attraction between two oppositely charged ions

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Isotope

Atoms of the same element with different numbers of neutrons and different masses

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Le Chatelier's principle

When a system in dynamic equilibrium is subjected to external change, the system readjusts itself to minimise the effect of the change and to restore equilibrium

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Limiting reagent

The reactant that is not in excess, which will be used up first and stop the reaction

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London forces

Attractive forces between induced dipoles in different molecules; also known as induced dipole dipole interactions

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Lone pair

An outer shell pair of electrons that is not involved in chemical bonding

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Mass number (a)

The sum of the number of protons and neutrons in the nucleus; also known as nucleon

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Metallic bonding

The electrostatic attraction between positive metal ions and delocalised electrons

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Concentration

The amount of solute in moles dissolved in one dm^3 (1000cm^3) of solution

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Molar gas volume (V_m)

The volume per mole of gas molecules at a stated temperature and pressure

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Molar mass (M)

The mass per mole of a substance in units of gmol^-1

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Mole

The amount of any substance containing as many elementary particles as there are carbon atoms in exactly 12g of the carbon-12 isotope, i.e. 6.02 x 10^23 particles

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Molecular formula

A formula that shows the number and type of atoms of each element present in a molecule

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Molecular ion

The positive ion formed in mass spectrometry when a molecule loses and electron

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Molecule

The smallest part of a covalent compound that can exist while retaining its chemical identity consisting of two or more atoms covalently bonded together

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Monomer

A small molecule that combines with many other monomers to form a polymer

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Neutralisation

The reaction between an acid and a base to produce a salt

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Nomenclature

A system of naming compounds

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Non polar

With no charge separation across a bond or in a molecule

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Nucleon number

The number of protons and neutrons in an atom (also known as mass number)

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Nucleophile

An atom or group of atoms that are attracted to an electron defficient carbon atom where it donates a pair of electrons to form a new covalent bond

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Nucleophillic substitution

A reaction in which a nucleophile is attracted to an electron defficient carbon atom and replaces an atom or group of atoms on it.

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Oxidation

Loss of electrons or an increase in oxidation number

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Oxidation number

A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived form a set of rules

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Oxidation state

The oxidation number

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Oxidising agent

A reagent that oxidises (takes electrons from) another species

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π (pi) bond

A bond formed by the sideways overlap of two p orbitals, containing two electrons and with the electron density concentrated above and below the line joining the nuclei of the bonding atoms

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Partial dissociation

The splitting of some of species in solution into aqueous ions

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Pauling electronegativity value

A value assigned as a measure of the relative attraction of a bonded atom for the pair of electrons in a covalent bond

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Percentage yield

Actual yield of products divided by theoretical yield of products x 100

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Periodicity

A repeating trend in properties of the elements across each period of the periodic table

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Periods

A horizontal row of elements in the periodic table. Elements show trends in properties across a period

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Permanent dipole

A small charge difference that does not change across a bond with positive and negative partial changes on the bonded atoms: the result of the bonded atoms having different electronegativities

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Permanent dipole-dipole interactions

Attractive forces between the permanent dipoles in different molecules

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Polar molecule

A molecule with an overall dipole having taken into account any dipoles across bonds and the shape of the molecule

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Polar covalent bond

A bond with a permanent dipole having positive and negative partial charges on the bonded atoms

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Polyatomic ion

An ion containing more than one atom

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Polymer

A large molecule formed from many thousands of repeat units of smaller molecules known as monomers

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Position of equilibrium

The relative quantities of reactants and products indicating the extent of a reversible reaction at equilibrium

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Primary

On a carbon atom at the end of a chain

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Primary alcohol

An alcohol in which the OH group is attached to a carbon atom that is attached to two or three hydrogen atoms

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Principle quantum number (n)

A number representing the relative overall energy of each orbital, which increases with distance from the nucleus. The set of orbitals with the same n-value are referred to as electron shells or energy levels

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Propagation

The steps that continue a free radical reaction, in which a radical reacts with a reactant molecule to form a new molecule and another radical causing a chain reaction.

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Proton number

The number of protons in the nucleus of an atom; also known as the atomic number

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Radical

A species with an unpaired electron

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Rates of reaction

The change in concentration of a reactant or a product in a given time

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Reaction mechanism

The sequence of bond breaking and bond forming steps that show the path taken by electrons during a reaction

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Redox reaction

A reaction involving reduction and oxidiation

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Reducing agent

A reagent that reduces (adds electrons to) another species

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Reduction

Gain of electrons or a decrease of oxidation number

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Reflux

The continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the contents of the flask boiling dry

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Relative atomic mass (A_r)

The weighted mean mass of an atom of an element compared to 1/12th of the mass of an atom of carbon-12

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Relative formula mass

The weighted mean mass of the formula units of a compound compared with 1/12th of the mass of an atom of carbon-12

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Relative isotopic mass

The mass of an isotope comapred with 1/12th of the mass of an atom of carbon-12

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Relative molecular mass (M_r)

The weighted mean mass of a molecule of a compound compared with 1/12th of the mass of an atom of carbon-12

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Reversible reaction

A reaction that takes place in both forward and reverse direction

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σ (sigma) bond

A bond formed by the overlap of one orbital from each bonding atom consisting of two electrons and with the electron density centred around a line directly between the nuclei of two atoms

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Salt

The product of a reaction in which the H+ ions from the acid are replaced by metal or ammonium ions

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Saturated

Containing single bonds only

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Second ionisation energy

The amount of energy required to remove one electron from each ion in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions

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Secondary

On a carbon atom to which two carbon chains are attached

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Secondary alcohol

An alcohol in which -OH group is attached to a carbon atom that is attached to two carbon chains and one hydrogen atom

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Shell (electron shell)

A group of atomic orbitals with the same principle quantum number (n) also known as a main energy level

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Shielding effect

The repulsion between electrons in different inner shells. Shielding reduces the net attractive force between the positive nucleus on the outer shell electrons

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Simple molecular lattice

A three dimensional structure of molecules bonded together by weak intermolecular forces

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Skeletal formula

A simplified organic formula with hydrogen atoms removed from alkyl chains leaving just carbon skeleton and associated functional groups

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Specific heat capacity (c)

The energy required to raise the temperature of one gram of a substance by 1K

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Standard enthalpy change of combustion ΔcHθ

The enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions with all reactants and products in their standard states

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Standard enthalpy change of formation ΔfHθ

The enthalpy change that takes place when one mole of compound is formed from its elements under standard condition with all reactants and products in their standard states

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Standard enthalpy change of neutralisation ΔneutHθ

The enthalpy change that accompanies the reaction of an acid by a base to form one mole of H_2O (l) with all reactants and products in their standard states

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Standard enthalpy change of reaction ΔrHθ

The enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard conditions with all reactants and products in their standard states

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Standard solution

A solution of known concentration

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Standard state

The physical state of substance under standard conditions of 100kPa and a stated temperature (usually 298K)

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Stereoisomer

Compounds with the same structural formula but with different arrangement of atoms in space

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Stochiometry

The ratio of the amount in moles of each substance in a chemical reaction

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Strong acid

An acid that dissociates completely in solution

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Structural formula

A formula showing the minimal detail for the arrangement of atoms in molecules

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Structural isomers

Compounds with the same molecular formula but different structural formulae

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Sub shell

A group of orbitals of the same type within a shell

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Substitution reaction

A reaction in which one atom or group of atoms is replaced by another atom or group of atoms

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Surroundings

Everything that is not the chemical system

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System

Everything - the atoms, molecules or ions - making up the chemical compounds being studied

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Termination

The step at the end of a radical substituion when two radicals combine to form a molecule

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Tertiary

On a carbon atom to which three carbon chains are attached

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Tertiary Alcohol

An alcohol in which the -OH group is attached to a carbon atom that is attached to no hydrogen atoms

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Theoretical Yield

The yield resulting from complete conversion of reactants into products

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Unsaturated

Containing multiple carbon-carbon bond

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Water of crystalisation

Water molecules that are bonded into a crystalline structure of a compound

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Weak acid

An acid that dissociates only partially in solution

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