AS level chemestry

chapter 3

unified atomic mass unit

one twelfth of an unbound neutral atom of the

carbon-12 isotope in its ground state.

The relative atomic mass

the ratio of the average mass of the atoms of an element to the unified atomic mass unit.

relative isotopic mass

the mass of a particular isotope of an element which has the Avogadro number of atoms (6.02 × 1023).

Stoichiometry

The calculation of reactant and product amounts in chemical reactions using balanced equations and mole ratios.

Balanced chemical equation

An equation in which the number of atoms of each element is the same on both sides, reflecting conservation of mass.

Mole (n)

The amount of substance containing Avogadro’s number of particles (6.022 × 10^23).

Avogadro constant (NA)

The number of particles in one mole of a substance (approximately 6.022 × 10^23).

The relative molecular mass Mr

the ratio of the weighted average mass of a molecule of a molecular compound to the unified atomic mass unit.

Relative formula mass (Mr)

The sum of the relative atomic masses of all atoms in a formula unit; used for ionic compounds.

Molar mass

a general term used for the mass in grams of 1 mole of a compound

Percentage composition by mass

the percentage by mass of a particular element in a compound

hydrated compound

A compound containing water of crystallisation

anhydrous compound

A compound which does not contain water of crystallisation

relative isotopic abundance

how much of each isotope is present

Empirical formula

The simplest whole-number ratio of atoms in a compound.

Molecular formula

The actual number of each type of atom in a molecule; may be a multiple of the empirical formula.

Theoretical yield

The maximum amount of product that could be formed from given reactants (based on stoichiometry).

Percentage yield

(Actual yield / Theoretical yield) × 100% — measures reaction efficiency.

compound ions

Ions that contain more than one type of atom

Limiting reagent

The reactant that is completely consumed first, limiting the amount of product formed.

Excess reagent

The reactant(s) remaining after the reaction has reached completion.

Atom economy

A measure of how efficiently a reaction uses all atoms of the reactants to form desired product.

Gas molar volume

The volume of a gas (24 dm^3 at room temperature and pressure, varies with conditions) per mole.