Same number of protons & electrons, different number of neutrons.
Relative Atomic Mass
The average mass of all isotopes compared to the mass of an atom of carbon-12.
Atomic & Proton Number
Atomic number: protons + neutrons
Proton number: protons (same as electrons)
A mole of a substance is defined by the amount of substance that contains as many particles as atoms in 12g of carbon-12 (Avogadro's constant).
The number of atoms in 12g of carbon-12: 6.02 x 10^23
Number of moles = mass in grams / molar mass in g/mol
mol = g / ram
Relative Molecular Mass
Sum of all the relative atomic masses of the atoms in one molecule.
The mass of ONE MOLE of a substance (g/mol) - Relative atomic mass.
Mol & gases
1 mole of any gas occupies 24 dm^3 at 25ºC and 1 atm (298K).