chem paper 1 definitions

define isotopes

atoms of the same element with a different number of neutrons

define relative atomic mass

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

define relative isotopic mass

the average mass of one atom of an isotope relative to 1/12th of the mass of one atom of carbon-12

define alkali

a substance that releases hydroxide ions in aqueous solution

define acid

a substance that releases protons in aqueous solution

define strong acid

an acid that fully dissociates in water

define weak acids

an acid that partially dissociates in water

define orbitals

a region that can hold up to two electrons

define ionic bond

the electrostatic attraction between positive and negative ions

define metallic bond

the attraction between positive ions and delocalised electrons

define covalent bond

a shared pair of electrons

define electronegativity

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

define periodicity

a repeating pattern of properties which is shown across different periods

define first ionisation energy

the energy needed to remove one electron from each atom in one mole of gaseous atoms

define disproportionation

where the same element is both oxidised and reduced

define activation energy

the minimum amount of energy required for a reaction to take place

define enthalpy change of formation

the enthalpy change when one mole of a substance is formed from its constituent elements in their standard states under standard conditions

define enthalpy change of combustion

the enthalpy change when one mole of a substance is completely burned in excess oxygen under standard conditions and all reactions and products in their standard states

define enthalpy change of neutralisation

the enthalpy change when an acid is neutralised by an alkali to form one mole of water under standard conditions and all reactants and products in their standard states

define average bond enthalpy

the energy required to break one mole of bonds in gaseous molecules

define catalyst

a substance that increases the rate of a chemical reaction by finding an alternative reaction pathway with a lower activation energy without being used itself

define homogenous catalyst

a catalyst in the same state as the reactants

define heterogeneous catalyst

a catalyst in a different state to the reactants

define bronsted-lowry acid

proton donor

define bronsted-lowry base

proton acceptor

define buffer

a solution which resists changes in pH when small amount of acid and alkali are added to it

define lattice enthalpy

the enthalpy change when one mole of an ionic compound is formed from its gaseous ions

define enthalpy change of solution

the enthalpy change when one mole of a substance is dissolved in water

define enthalpy change of hydration

the enthalpy change when one mole of aqueous ions is formed from one mole of gaseous ions

define oxidation

increase in oxidation number or loss of electrons

define oxidising agent

a substance which gains electrons and is itself reduced

define reduction

decrease in oxidation number or gain of electrons

define reducing agent

a substance which loses electrons and is itself oxidised

define transition element

an element which forms at least one ion with a partly filled d subshell

define complex ions

consist of a metal ion which is bonded to a number of ligands by dative covalent bonds

define bidendate ligans

a species which donates two electron pairs to a metal ion to form two dative covalent bonds