Chemistry AS definition

relative atomic mass

the weighted mean mass of an atom of an element compared with 1/12th of the mass of C-12

Lattice dissociation enthalpy

The enthalpy change when one mole of ionic compound is completely dissociated into its gaseous constituent ions under standard condition.

Relative isotopic mass

The mass of an atom of an isotope compared with 1/12th of the mass of C-12

Le Chatelier’s principle 

If a change is made to a system in dynamic equilibrium, the position of the equilibrium moves to counteract this change

Avogadro constant

6.02 × 10²³ (particles per mole)

Empirical formula

The 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

Weak acid

Partially dissociated, proton donor

Enthalpy change of formation

The enthalpy change when 1 mole of compound is formed form its elements in their standard states under standard conditions

Enthalpy change of combustion

The energy required when one mole of substance is completely burnt in oxygen

Enthalpy change of neutralisation

The energy released for one mole of water form from neutralisation reaction

Average bond enthalpy

The energy required to break one mole of a given bond in gaseous molecules, averaged over many compounds

Enthalpy change of solution

The energy required when one mole of solute dissolves in solvent

Enthalpy change of hydration

The energy released when one mole of gaseous ions is dissolved in water

Lattice enthalpy

The energy released when one mole of an ionic compound is formed from its gaseous ions under standard conditions

Oxidizing agent

Electron acceptor/ is reduced

Reducing agent

An electron donor/ is oxidized

Hess Law

If 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.

First ionization energy

The energy required to remove one mole of electrons form 1 mole of gaseous atoms, forming one mole of gaseous +1 ions

Homologous series

A series of organic compounds with the same functional group but with each successive member differing by CH2

Functional group

A group of atoms responsible for the characteristic reactions of a compound

Aliphatic

A compound containing carbon and hydrogen joined together in straight chains, branched chains or non-aromatic rings.

Alicyclic

An aliphatic compound arranged in non-aromatic rings with or without side chains.

Aromatic

A compound containing a benzene ring

General formula

The simplest algebraic formula of a member of a homologous series

Structural formula

The minimal detail that shows the arrangement of atoms in a molecule

Displayed formula

The relative positioning of atoms and bonds between them

Skeletal formula

The simplified formula that removed hydrogen and form the chain, leaving carbon skeleton and related functional group.

Homolytic fission

When a covalent bond breaks, each bonding atom receives one electron each from the bonded pair, forming 2 free radicals.

Heterolytic fission

When a covalent bond breaks, one of the bonding atom receives both electrons from the bonded pair

Radical

A species with an unpaired electron

E/Z isomerism

The restricted rotation about a double bond, each carbon atom of the C=C has 2 different group to be attach to each.

Cis-trans isomerism

A special type of E/Z isomerism which 2 of the groups attached to each carbon atom off the C=C double bond are the same

Electrophile

An electron pair acceptor

Nucleophile

An electron pair donor

Electronegativity

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

Conjugate pair

A pair of substance that differ by one proton

buffer

Solution that minimises pH changes when small amount of acid or base is added.

Giant metallic lattice

A strong electrostatic attraction between metal cations and delocalised electron

Ionic bonding

The electrostatic attraction between positive and negative ions.

Simple molecular (covalent bond)

Strong electrostatic force attraction between a shared pair of electrons and their positive nuclei

Sigma bond (different from pi bond)

Has direct overlap, is between atoms, higher bond enthalpy than Pi bond.

Pi bond (different from Sigma bond)

Is below and above bonding atom, have sideway overlap orbitals, lower bond enthalpy than Sigma bond