CHEMISTRY Definitions (IEB South Africa) :)

Molar Mass

The mass in grams of one mole of that substance.

A Solution

A homogenous mixture of solute and solvent.

The Solute

The substance that is dissolved in the solution.

The Solvent

The substance in which another substance is dissolved, forming a solution.

Molar Concentration

The amount of solute per unit volume of solution.

IntRAmolecular Bond

A bond between atoms within molecules.

Electronegativity

A measure of the tendency of an atom to attract a bonding pair of electrons.

Covalent Bond

A sharing of at least one pair of electrons by two atoms.

Ionic Bonding

A transfer of electrons to form cations and anions which are electrostatically attracted in an ionic crystal lattice.

Metallic Bonding

The attraction between positive kernels and a sea of delocalised electrons.

IntERmolecular Force

A force of attraction between molecules or between atoms of noble gases.

Heat of Reaction (\Delta H)

The net change of chemical potential energy of the system.

Exothermic Reactions

Reactions which transform chemical potential energy into thermal energy.

Endothermic Reactions

Reactions which transform thermal energy into chemical potential energy.

Activation Energy

The minimum energy required to start a chemical reaction./The energy required to form the activated complex.

Activated Complex

A high energy, unstable transition state between the reactants and the products.

Reaction Rate

The change in amount or concentration per unit time of either a reactant or product.

Catalyst

A substance that increases the rate of the reaction but remains unchanged at the end of the reaction.

Organic Molecules

Molecules containing carbon atoms, with the exception of carbon dioxide, carbon monoxide, diamond, graphite, carbonates (or bicarbonates), carbides (e.g. CaC2) and cyanides (e.g. KCN).

Hydrocarbon

A compound containing only carbon and hydrogen atoms.

Saturated Compound

A compound in which all of the bonds between carbon atoms are single bonds.

Unsaturated Compound

A compound in which there is at least one double and/or triple bond between carbon atoms.

Functional Group

An atom or group of atoms that form the centre of chemical activity in the molecule.

Homologous Series

A serious of similar compounds which have the same functional group and have the same general formula, in which each member differs from the previous one by a single CH2 unit.

Structural Isomers

Compounds having the same molecular formula but different structural formulae.

Substitution Reactions

Reactions when one atom or molecular fragment is replaced in a molecule by another.

Elimination Reactions

A reaction where atoms or molecular fragments are removed from adjacent carbon atoms on a molecule leaving a double bond with nothing else having been added.

Addition Reactions

A reaction where a double bond opens and new molecular fragments are added to the molecule at both ends of the double bond without anything being removed.