AS Chemistry F321 Key Definitions:

Module 1- Atoms and reactions:

Isotopes-are atoms of the same element, with same number of protons and different numbers of neutrons.
Atomic (proton) Number- is the number of protons in the nucleus of an atom.
Mass (Nucleon) Number- is the number of particles (protons and neutrons) in the nucleus of an atom.
An Ion- is a positively charged or negatively charged atom or (covalently bonded) groups of atoms (a molecular ion).
Relative Isotopic mass- is the weighted mean mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12.
Relative atomic mass-Ar is the weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of carbon-12.
Relative molecular mass, Mr, is the weighted mean mass of a molecule compared with one twelfth of the mass of an atom of carbon-12.
Relative formulae mass- if the weighted mean mass of a formula unit compared with one twelfth of the mass of an atom of carbon-12.
Amount of Substance- is the quantity whose unit is the mole. Chemists use amount of substance as a means of counting atoms.
The Avogadro’s Constant, Na, is the number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol -1)
A Mole-is the amount of any substance containing as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope.
Molar mass, Mr is the mass per mole of a substance. The units of molar mass are g mol -1.
The Empirical formulae- is the simplest whole number ratio of atoms of each element present in a compound.
A Molecule -is a small group of atoms held together by covalent bonds.
The Molecular formula- is the actual number of atoms of each element in a molecule.
Molar Volume- is the volume per mole of a gas. The units of molar volume are dm-3 mol -1. At room temperature and pressure (RTP), the molar volume is approximately 24.0 dm-3 mol -1.
The concentration- of a solution is the amount of solute, in mol, dissolves per 1 dm3 (1000cm3) of solution.
A Standard solution- is a solution of known concentration. Standard solutions are normally used in titrations to determine unknown information about another substance.
A species -is any type of particle that takes part in a chemical reaction.
Stoichiometry -is the molar relationship between the relative quantities of substances taking part in a