GCE Chemistry clarification of terms

Molecular ion

Two or more atoms covalently bonded with an overall charge.

Avogadro constant

Number of atoms in 12.000g of carbon-12.

Mole

The amount of substance which contains the Avogadro constant of atoms, molecules or groups of ions.

Molar mass

The mass of one mole of a substance.

Anhydrous (salt)

A salt which contains no water of crystallisation.

Hydrated (salt)

A salt which contains water of crystallisation.

Water of crystallisation

Water chemically bonded within a crystal structure.

Atomic number

The number of protons in (the nucleus of) an atom.

Mass number

The total number of protons and neutrons in (the nucleus of) an atom.

Relative atomic mass (RAM)

The average (weighted mean) mass of an atom of an element relative to one-twelfth of the mass of an atom of carbon-12.

Relative isotopic mass (RIM)

The mass of an atom of an isotope of an element relative to one-twelfth of the mass of an atom of carbon-12.

Isotopes

Atoms which have the same atomic number but a different mass number.

Relative formula mass (RFM)

The average (weighted mean) mass of a formula unit relative to one-twelfth of the mass of an atom of carbon-12.

Relative molecular mass (RMM)

The average (weighted mean) mass of a molecule relative to one-twelfth of the mass of an atom of carbon-12.

First ionisation energy

The energy required to convert one mole of gaseous atoms into gaseous ions with a single positive charge.

Second ionisation energy

The energy required to convert one mole of gaseous ions with a single positive charge into gaseous ions with a double positive charge.

Third ionisation energy

The energy required to convert one mole of gaseous ions with a double positive charge into gaseous ions with a triple positive charge.

Covalent bond

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

Co-ordinate (Dative) bond

A shared pair of electrons between two atoms where one atom provides both electrons.

Octet rule

When reacting, an atom tends to gain, lose or share electrons to achieve eight in its outer shell.

Electronegativity

The extent to which an atom attracts the bonding electrons in a covalent bond.

Polar bond

A covalent bond in which there is unequal sharing of the bonding electrons.

Delocalised electrons

Outer electrons which do not have fixed positions but move freely.

Intermolecular

Between neighbouring molecules.

van der Waals’ forces

The attraction between instantaneous and induced dipoles on neighbouring molecules.

Permanent dipole-dipole attraction

Attraction between the positive end, δ+, of the permanent dipole on a molecule with the negative end, δ-, of the permanent dipole of a neighbouring molecule.

Hydrogen bond

The attraction between a lone pair of electrons on a very electronegative atom (i.e. N,O, F) in one molecule and a hydrogen atom in a neighbouring molecule, in which the hydrogen atom is covalently bonded to a very electronegative atom (N,O,F).

Redox

Oxidation and reduction occur in the same reaction.

Oxidation

Loss of electrons/Increase in oxidation state.

Reduction

Gain of electrons/Decrease in oxidation state.

Oxidising agent

Electron acceptor.

Reducing agent

Electron donor.

Disproportionation

Oxidation and reduction of the same element in the same reaction.

Strong acid/base

Fully dissociates in solution.

Weak acid/base

Partially dissociates in solution.

Molarity

Concentration in mol dm-3 expressed using M.

Concentration

Number of moles or mass present in a stated volume.

Standard solution

A solution for which the concentration is known.

Empirical formula

A formula which shows the simplest whole number ratio of atoms of each element in a compound.

Molecular formula

A formula which shows the actual number of atoms of each element in a molecule.

Molar gas volume

The volume of one mole of gas under specified conditions of temperature and pressure.

Percentage yield

(actual yield/theoretical yield)x100

Atom economy

(mass of desired product/total mass of products)x100

Homologous series

Compounds which have the same general formula and similar chemical properties.

Functional group

Reactive group within a compound.

Structural isomers

Molecules which have the same molecular formula but a different structural formula.

Geometric isomers

Molecules with the same structural formula but different arrangements due to C=C bonds.

Saturated hydrocarbon

Contains no C=C or C≡C bond.

Hydrocarbon

Contains only hydrogen and carbon.

Substitution

Replacing one atom or group with a different atom or group.

Homolytic fission

Bond breaking in which one of the shared electrons goes to each atom.

Heterolytic fission

Bond breaking in which both electrons in the shared pair go to a single atom.

Radical

A particle with an unpaired electron.

Unsaturated hydrocarbon

Contains at least one C=C or C≡C bond.

Sigma bond

A covalent bond formed by the linear overlap of atomic orbitals.

Pi bond

A covalent bond formed by the sideways overlap of p orbitals.

Bond length

The distance between the nuclei of two covalently bonded atoms.

Hydrogenation

Addition of a hydrogen molecule across a C=C.

Electrophile

An ion or molecule that attacks regions of high electron density.

Primary carbocation

A carbocation with one carbon atom directly bonded to the positively charged carbon.

Secondary carbocation

A carbocation with two carbon atoms directly bonded to the positively charged carbon.

Tertiary carbocation

A carbocation with three carbon atoms directly bonded to the positively charged carbon.

Polymerisation

Joining together of many small molecules (monomers) to form a large molecule.

Monomers

Small molecules that join together to form a polymer.

Polymer

A large molecule formed when monomers join together.

Primary halogenoalkane

A halogenoalkane which has one carbon atom directly bonded to the carbon that is bonded to the halogen.

Secondary halogenoalkane

A halogenoalkane with two carbon atoms directly bonded to the carbon that is bonded to the halogen.

Tertiary halogenoalkane

A halogenoalkane with three carbon atoms directly bonded to the carbon that is bonded to the halogen.

Reflux

Repeated boiling and condensing of a (reaction) mixture.

Hydrolysis

Breaking up molecules by reaction with water.

Nucleophile

An ion or molecule with a lone pair of electrons, that attacks regions of low electron density.

Elimination

A reaction in which a small molecule is removed from a larger molecule.

Miscibility

Liquids which mix in all proportions.

Primary alcohol

An alcohol with one carbon atom bonded to the carbon that is bonded to the –OH group.

Secondary alcohol

An alcohol with two carbon atoms bonded to the carbon that is bonded to the –OH group.

Tertiary alcohol

An alcohol with three carbons bonded to the carbon that is bonded to the –OH group.

Ground state (infrared spectroscopy)

A molecular vibration in the lowest possible energy state.

Wavenumber

The reciprocal of the wavelength measured in cm-1.

Endothermic

A reaction where the enthalpy of the products is greater than that of the reactants.

Exothermic

A reaction where the enthalpy of the products is less than that of the reactants.

Standard conditions

298K and 100kPa.

Standard enthalpy change

Change in heat energy at constant pressure, measured at standard conditions.

Standard enthalpy of combustion

The enthalpy change when one mole of a substance is completely burnt in oxygen under standard conditions.

Standard enthalpy of formation

The enthalpy change when one mole of a compound is formed from its elements under standard conditions.

Standard enthalpy of neutralisation

The enthalpy change when one mole of water is produced in a neutralisation reaction under standard conditions.

Conservation of energy

Energy cannot be created or destroyed but can change from one form to another.

Hess’s Law

The enthalpy change for a reaction is independent of the route taken, provided initial and final conditions are the same.

Average bond enthalpy

The energy required to break one mole of a given bond averaged over many compounds.

Reaction rate

The change of concentration of a reactant or product with respect to time.

Catalyst

A substance that increases the rate of a chemical reaction but is not consumed.

Activation energy

The minimum amount of energy required for a reaction to occur.

Reversible

A reaction which goes in both forward and backward directions.

Dynamic (equilibria)

Rate of forward reaction equals the rate of the backward reaction.

Equilibrium

A reversible reaction where the amount of each reactant/product remains constant.

Homogeneous

A reaction where all the reactants and products are in the same physical state.

Heterogeneous (equilibria)

A reaction where not all reactants and products are in the same physical state.

Kc

The equilibrium constant for a reaction in the format aA + bB ⇌ cC + dD.

Heterogeneous (catalyst)

The catalyst is in a different phase from the reactants.

s-block element

An element with the highest energy/outer electron in an s-subshell.

Solubility

The maximum mass of solute that dissolves in 100 g of solvent at a stated temperature.