atomic weight?

[angelronnie]

Dear People,
Please help me if i have theright definition of atomic weight...(i am rather new in science)
a.The atomic weight is approximately the sum of the number of protons and neutrons found in the nucleus of an atom;
b.Atomic weight is the relative mass of an atom of the given element compared to the mass of carbon-12;
c.The average mass of the atoms of an element.
are all these three definitions right? :cry:
please help

[liuboy]

strictly speaking, the referance of the atomic mass is 1/12 of carbon-12, so approximately, the atomic mass is the sum of the protons and nuetrons in nuclei. What's more, every element has one or more isotopes in nature, so we have to calculate the contribution of each isotope, that is to say, the average mass of all the isotopes of the same element gives the final atomic mass of one element.
Is my answer understandable?

[angelronnie]

thank you so much. i understand