Relative Atomic Mass

[hElPsEeKeR15]

I do know how to determine it and also know what it is. But according to the definition, "Relative atomic mass is the ratio of the average atomic mass of an element to 1/12th of carbon 12 atom", Carbon 12 has been chosen as the reference. My question is that when we are to find out Ar of an element we don't use Carbon 12 in any step of calculations(so far i know). So, then what is the role of Carbon 12? I mean how we use it in calculations or in finding out Ar?
Please someone satisfy my query......

 

[intelnehalem]

Carbon-12 is known to have an EXACT atomic mass of 12. All the other atomic masses are based on this.
ex: Hydrogen(Ar=1) has a Atomic mass 12 times less than Carbon-12
Its not necessary to use in calculations since Ar is given in the periodic table Its rather used to explain how Ar for the different elements are obtained

 

[hElPsEeKeR15]

Can you please specify how are atomic masses based on it?
Also there are some elements whose Ar are more than Hydrogen's. How would you explain this then???

 

[intelnehalem]

Its like this:
Hydrogen has a Ar 12 times less than Carbon
Calcium has an Ar 40 time MORE THAN HYDROGEN
So the other elements are based on this

 

[PrInCeSs AshLeY]

I’ll try to explain.
We have different units for measuring masses, like gram, kilogram etc. But an atom is too light and these units are not suitable.
So a carbon atom was taken and was divided into twelve pieces and the mass of each piece was taken as one unit. These means, that total mass of carbon is twelve.
You must be aware of this word “isotopes”. So isotopic abundance of Carbon-12 atom (This means Carbon atom with a relative atomic mass of 12) is present in a very high percentage than other carbon isotopes. This is why it was chosen as the standard atom.
So now, if someone wants to find mass of... say oxygen, then he'll divide oxygen into pieces (each piece must be equal to that of 1 piece of carbon-12 atom) and then count the number of pieces. As he'll get 16 pieces, this means that the AR of oxygen atom is 16.
I hope you are getting me, or do you want me to use more simple language?

 

[hElPsEeKeR15]

Wow what an explanation!
I got the point. Thanks Ashley.

 

[PrInCeSs AshLeY]

You are always welcome. Anything else about which you are confused?

 

[hElPsEeKeR15]

I have posted a new topic please visit it.

 

[PrInCeSs AshLeY]

Yep I have answered.

 

[intelnehalem]

I’ll try to explain.
We have different units for measuring masses, like gram, kilogram etc. But an atom is too light and these units are not suitable.
So a carbon atom was taken and was divided into twelve pieces and the mass of each piece was taken as one unit. These means, that total mass of carbon is twelve.
You must be aware of this word “isotopes”. So isotopic abundance of Carbon-12 atom (This means Carbon atom with a relative atomic mass of 12) is present in a very high percentage than other carbon isotopes. This is why it was chosen as the standard atom.
So now, if someone wants to find mass of... say oxygen, then he'll divide oxygen into pieces (each piece must be equal to that of 1 piece of carbon-12 atom) and then count the number of pieces. As he'll get 16 pieces, this means that the AR of oxygen atom is 16.
I hope you are getting me, or do you want me to use more simple language?

^To add to the above, Carbon-12 has an exact atomic mass unit(amu) of 12

 

[PrInCeSs AshLeY]

@ intelnehalem, guess this is obvious because if you are diving that atom into twelve equal pieces and then considering the mass of one piece as one standard unit, and then adding up the masses of all those pieces, you are going to get "12" as your answer.

 

[intelnehalem]

@ intelnehalem, guess this is obvious because if you are diving that atom into twelve equal pieces and then considering the mass of one piece as one standard unit, and then adding up the masses of all those pieces, you are going to get "12" as your answer.

Well, this maybe obvious for many people but it may very well not be the same for some
Well, the one standard unit you're referring to is the mass of a Neutron/Proton(same mass) Guess that's obvious too xD

 

[PrInCeSs AshLeY]

I don't know if it's obvious or not but well I know that a proton/neutron has a mass 1 a.m.u