proton number/atomic number
the number of protons in the nucleus of an atom and indicates the elements position in the periodic table
nucleon number/mass number
the number of protons and neutrons found in the nucleus of an atom of an element
orbital
the volume of space in which there is a 95% chance of finding an electron
isotopes
atoms of the same element with the same number of protons, but different number of neutrons
the first ionisation energy
the enthalpy change required to move one mole of electrons from one mole of gaseous atoms to form one mole of gaseous unipositive cations.
the second ionisation energy
enthalpy change required to remove one mole of electrons from one mole of gaseous univalent cations to form one mole of unipositive cations.