Relative Atomic Mass
The relative atomic mass is the (weighted) mean mass of an atom of an element, compared to 1/12th the mass of an atom of Carbon-12.
Relative Isotopic Mass
The relative isotopic mass is the mass of an isotope of an element relative to 1/12th the mass of an atom of Carbon-12.
First Ionisation Energy
First ionisation energy is the energy needed to remove 1 electron from each atom in 1 mole of gaseous atoms, to form 1 mole of gaseous 1+ ions.
Electronegativity is a measure of how strongly an atom can attract the bonded pair of electrons.
Isotopes are atoms of the same element/same number of protons, with a different number of neutrons/different mass number.
Molar Mass is the mass per mole of a substance.
The Empirical Formula is the simplest whole number ratio of atoms in each element present in a compound.
The Molecular Fomula is the actual number of atoms of each element in a molecule.