# Mass number and relative atomic mass?

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#1
I know mass numbers and relative atomic numbers are different: the mass number is the number of protons and neutrons in an atom and the RAM is the average weighted mass of the isotopes of that element when compared with carbon-12. What I don't understand is why on the Periodic Table they're the same number? Could you therefore say when referencing to the Perioidc table that the mass number/ram are the same number? Is this always the case? (I'm doing GCSE Chemistry)
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5 years ago
#2
Relative atomic mass is the weighted mean mass of all atoms of an element compared with 1 12th the mass of an atom of carbon 12. Atomic mass is the amount of protons and neutrons and this can vary for isotopes of an element so as a result atomic mass can change and so dont always equal relative atomic mass,however in a periodic table they treat the atomic mass as the average of all the different isotope atomic mass of an element. The relative atomic mass is as a result the same in this scenario as the atomic mass.
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5 years ago
#3
(Original post by Squigysqump)
I know mass numbers and relative atomic numbers are different: the mass number is the number of protons and neutrons in an atom and the RAM is the average weighted mass of the isotopes of that element when compared with carbon-12. What I don't understand is why on the Periodic Table they're the same number? Could you therefore say when referencing to the Perioidc table that the mass number/ram are the same number? Is this always the case? (I'm doing GCSE Chemistry)
They aren't actually the same but probably will be at 2dp or whatever the sf is on your periodic table.
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5 years ago
#4
On a GCSE periodic table, check out chlorine's and copper's masses.

Also remember that mass number (of one isotope) can NEVER be anything but a whole number (since it is the proton and neutron count).

Bromine is another fun one, its two stable isotopes have masses of 79 and 81. What is the RAM? What do you notice? How could that have happened?
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