Chem Definitions

Relative Isotopic Mass

Mass of 1 atom of the isotope relative to 1/12 the mass of one carbon-12 atom

Relative atomic mass

The average mass of one atom of an element relative to 1/12 the mass of one carbon-12 atom

Relative formula mass

The average mass of 1 formula unit of the substance relative to 1/12 of one atom of carbon-12

Relative molecular mass

The average mass of one molecule relative to 1/12 the mass of one carbon-12 atom

Isotopes

Elements with same atomic number but different mass number

Empirical formula

Simplest whole number ratio of the elements present in 1 molecule or formula unit of a compound

Molecular formula

The actual number of each of the different atoms present in a molecule

Isoelectronic

Different species with the same number of electrons

Metallic bonding

The electrostatic attraction between a lattice of positive ions and a sea of delocalised electrons

Ionic bonding

Electrostatic forces of attraction between oppositely charged ions

Covalent bonding

Electrostatic forces of attraction between a pair of shared electrons and the positively charged nuclei

Hybridisation

The process of mixing valence atomic orbitals of an atom to form hybrid orbitals

Bond length

The distance between the nuclei of two bonded atoms in a covalent bond

Bond energy

The energy required to break 1 mole of covalent bond between two atoms in gaseous states

Electronegativity

The ability for an atom to attract bonded electrons to itself

Enthalpy change of reaction

The enthalpy change required when molar quantities of reactants in a chemical equation react to form products at standard conditions of 298K and 1 bar

Enthalpy change of atomisation (Element)

The enthalpy change required to form one mole of gaseous atoms from its elements at standard states in standard conditions of 298K and 1 bar.

Enthalpy change of atomisation (Compounds)

The enthalpy change required to form gaseous atoms from one mole of substance at standard conditions of 298K and 1 bar.

Enthalpy change of combustion

The enthalpy change required to burn one mole of substance completed in excess oxygen at standard conditions of 298K and 1 bar

Standard enthalpy change of formation

The enthalpy change required to form one mole of substance from its constituent elements in their standard states at standard conditions of 298K and 1 bar

Enthalpy change of Neutralisation

The enthalpy change when an acid reacts with a base to form one mole of water in dilute aqueous solution at standard conditions of 298K and 1 bar

Lattice energy

The energy evolved when one mole of solid ionic compound is formed from its constituent gaseous ions

Ionisation Energy

The energy required to remove one mole of electrons from one mole of gaseous atom to form one mole of gaseous singly charged cation

Electron affinity

The energy required when one mole of gaseous atoms gains one mole of electrons to form one mole of gaseous singly charged anions

Enthalpy change of hydration

Enthalpy change when one mole of gaseous ions is dissolved in a large amount of water to form one mole of aqueous ions at 298K and 1 bar.

Enthalpy change of solution

Enthalpy change when one mole of substance is completely dissolved in a large excess of solvent to form an infinitely dilute solution at 298K and 1 bar

Entropy

The measure of the degree of disorder of a system

Gibbs free energy change of reaction (G)

Maximum amount of energy that is available to do work under standard conditions of 298K and 1 bar

Rate of reaction

Change in concentration of reactants consumed or products formed per unit time

Rate equation

A mathematical expression that related to rate of reaction to the concentration of reactants raised to an appropriate power

Rate constant

The proportionality constant in a rate equation given its temperature

Order of reaction

The power to which concentration of reactants in a rate equation are raised to

Overall order of reaction

The sum of the powers of the concentration terms in the rate equation

Half life

Time taken for the concentration of reactants to fall to half of its initial concentration

Activation energy

The minimum amount of energy reactant particles need to possess for a reaction to occur

Catalyst

A substance that increases the rate of a chemical reaction without chemically changing itself at the end of the reaction

Dynamic equilibrium

When a reversible reaction has reached dynamic equilibrium, the forward rate of reaction is equal and non zero to the backward rate of reaction given no net change of concentration of reactants and products

Le Chatlier’s Principle

If a system at dynamic equilibrium is subjected to a change, the system will react to reduce the effect of the change, re-establishing equilibrium

Empirical formula

Simplest ratio of the number of atoms of elements present in one molecule

Molecular formula

Actual number of atoms of elements present in one molecule

Structural formula

Shows how the constituent atoms of a molecule are joined together without any ambiguity

Full structural/ Displayed formula

Shows the detailed structure of the molecule showing the relative placing of atoms and the number of bonds between them

Skeletal formula

Shows the simplified representation of the structural formula by removing hydrogen atoms and its associated bonds with carbon atoms from alkyl chains, leaving just the carbon - carbon bond in the carbon skeletal and their associated functional groups

Stereochemical structure

Shows the spatial arrangement of bonds, atoms and groups in a molecule in 3D

Functional groups

Atoms or groups of atoms in an organic compound that determines its chemical properties

Free radical

An atom or groups of atoms containing an unpaired electron formed from the homolytic fission of a covalent bond

Carbocation

An ion with a positively charged carbon atom

Electrophile

An electron pair acceptor

Nucleophile

An electron pair donor

Homolytic fission

The breaking of covalent bonds such that one electron goes to each of the atoms, forming free radicals

Heterolytic fission

The breaking of covalent bonds such that both electrons goes to the same atom, usually involving ions

Constitutional isomer

Compounds with the same molecular formula but different structural formula

Stereoisomers

Compounds with the same molecular and structural formula but different arrangements of atoms or groups of atoms in space

Enantiomers

Compounds with the same molecular and structural formula but they are non-super imposable mirror images of each other

Arrhenius acid

A substance that produced H+ ions in aqueous solution

Arrhenius base

A substance that produces OH- ions in aqueous solution

Bronsted Lowry Acid

A proton donor

Bronsted Lowry Base

A proton acceptor

Lewis Acids

An electron acceptor

Lewis Base

An electron donor

Buffer solution

A solution whose pH remains almost unchanged when a small amount of H+ or OH- is added to it

Polymers

Polymers are macromolecules built up from monomers, with average molar mass of at least 1000 or at least 100 repeat units

Standard cell potential

The potential of a cell measured when both half cells are under standard conditions

Standard electrode potential

The potential difference measured at 298K between a standard hydrogen electrode and a half cell in which the concentration of any reacting species is 1 moldm-3 and any gaseous species is at 1 bar

Solubility

Solubility of a sparingly soluble salt is the maximum amount of solute that can dissolve in 1dm3 solution

Transition element

Transition element is a d-block element whose atom has an incomplete d subshell, or which can give rise to cations with an incomplete d subshell

Complex

A complex contains a central metal atom or ion dative bonded to one or more surrounding molecules or anions called ligands

Ligand

A ligand is an ion or molecule which contains at least one atom bearing a long pair of electrons which can be donated into a low lying vacant orbital of a central metal atom or ion to form a dative covalent bond, forming a complex

Ligand exchange

Ligand exchange occurs when one ligand displaces another ligand from the metal complex