An atom is the smallest particle of an element which can take part in a chemical reaction
A molecule is the smallest particle of a substance that can normally exist alone and still retain the chemical properties of that substance, Be it an element or a compound.
Isotopic mass is the mass of an isotope of an element
Atomic mass is the mass of an atom.The relative atomic mass,A of an element is the number of times the average mass of one atom of that element is heavier than one-twelfth the mass of one atom of carbon-12
Molecular mass is the mass of a given molecule. The relative molecular mass,M, of an element or a compound is the number of times the average mass of one molecule of it is heavier than one-twelfth the mass of one atom of carbon-12
One mole of a substance is the amount containing as many elementary entities as the number of atoms in exactly 12 grams of Carbon-12 .
The molar mass of any substance is the mass of one mole of that substance expressed in grams
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