IB Chem SL Definitions

Relative atomic mass (Ar)

The relative atomic mass of an element is the weighted average of the masses of the isotopes relative to 1/12 of the mass of a carbon 12 atom.

Relative molecular mass (Mr)

The relative molecular mass of a substance is the mass of one molecule of that substance relative to 1/12 of the mass of carbon–12 atom.

Mass Number

The sum of the protons and neutrons in the nucleus of the atom or ion.

Atomic Number

Is equal to the number of protons in the nucleus of an atom.

Isotope

are atoms of the same element with different numbers of neutrons.

1st Ionisation Energy

The minimum energy required to remove one mole of electrons from an atom in its gaseous state.

Electronegativity

Electronegativity is a measure of the tendency of an atom in a molecule to attract a bonding pair of electrons towards itself.

Exothermic Reaction

An exothermic reaction is one that releases heat to the surroundings. (As a result of forming products with stronger bonds than the reactants. Exothermic reactions have negative ∆H values.)

Endothermic Reaction

An endothermic reaction is one that absorbs heat from its surroundings.$(As a result of forming products with weaker bonds than the reactants. Endothermic reactions have positive ∆H values.)

Standard state

The standard state of an element or compound is its most stable state under the specified conditions.

Standard enthalpy change of a reaction

The standard enthalpy change (ΔH θ) is the heat energy transferred under standard conditions (pressure 101.3 kPa, temperature 298 K) for a reaction.

Average Bond Enthalpy

This is the energy required to break one mole of the same type of bond in the gaseous state averaged over a variety of similar compounds.

Rate of Reaction

The increase in concentration of products or the decrease in concentration of reactants per unit time.

Activation Energy

The minimum energy needed (by reactants) to start/initiate a reaction.

Bronsted Lowry Acid

An acid is a proton (hydrogen ion) donor.

Bronsted Lowry Base

A base is a proton (hydrogen ion) acceptor.

Oxidation

The loss of electrons from a species during a chemical reaction.

Reduction

The gain of electrons by a species during a chemical reaction.

Oxidising Agent

A species that brings about oxidation by removing electrons from another reactant. During the reaction the oxidizing agent gains electrons and so is reduced.

Reducing Agent

A species that brings about reduction by giving electrons to another reactant. During the reaction the reducing agent loses electrons and so is oxidized.