Chemistry AS terminology

Isotope

atoms of the same element with a different number of neutrons and a different mass

relative atomic mass

weighted mean mass of an atom compared with 1/12th mass of carbon-12

relative isotopic mass

mass of an atom of an isotope compared to 1/12th mass of carbon-12

atomic orbitals

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

empirical formula

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

molecular formula

the number and type of atoms of each element in a molecule

water of crystallisation

water that occurs in crystals but is not covalently bonded to a host molecule or ion

anhydrous

contains no woc

hydrated

contains woc

standard solution

solution of known concentration

acids

release H+ ions in aqueous solutions

ionic bonding

electrostatic attraction between + and - ions

covalent bonding

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

dative covalent bonding

when lone pair is donated to empty space in atom

giant ionic lattice

due to oppositely charged ions strongly attracted in all direction

electronegativity

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

polar molecule

requires polar bonds with dipoles that do not cancel due to their direction

metallic bonding

strong electrostatic attraction between cations and delocalised electrons

disproportionation

when an element is both ox and red in reaction

first ionisation energy

energy required to remove one mole of electrons from one mole of atoms in the gaseous state to form one mole of gaseous 1+ ions

Homologous series

series of org compounds with same functional group differing by a CH₂ each

aromatic

contains benzene ring

alicyclic

compounds/carbons bonded in a ring (not benzene)

aliphatic

compounds branched/unbranched/non aromatic rings

structural isomer

same molecular formula but different structural formula

homolytic fission

each bonding atom receives one electron from the bonding pair, forming 2 radicals

heterolytic fission

one bonding atom receives both electrons from the bonded pair

radical

species with unpaired electron

stereoisomerism

compounds with same structural formula but diff arrangement in space

Sigma bond

Overlap of orbitals directly between bonding atoms, free rotation

Pi bond

Sideways overlap of adjacent p orbitals above and below bonding c atoms

Electrophile

An electron pair accepter

Nucleophile

Electron pair donor

Standard conditions

100KPa and 298K

Standard state

Physical state under standard conditions

Enthalpy change of reaction

Enthalpy change associated with stated equation

Enthalpy change of formation

Formation of 1 mol of a compound form its elements

Enthalpy change of combustion

Complete combustion of 1 mol of a substance

Enthalpy change of neutralisation

Formation of 1 mol of water from neutralisation

Standard [-]

Under standard conditions with all R and P in standard states

Average bond enthalpy

Energy required to break one mol of bonds in gaseous molecules

Exothermic reaction

More energy released forming bonds than is taken to break bonds

Endothermic reaction

Less energy released forming bonds than is taken to break bonds

Activation energy

Minimum amount of energy required for a reaction to occur