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# Chemistry confusion watch

1. My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
2. Sum of number of protons and neutrons.
3. (Original post by haarithiop)
Sum of number of protons and neutrons.
Yes i know thats the mass number but whats relative atomic mass?
4. (Original post by HN786)
Yes i know thats the mass number but whats relative atomic mass?
Why ask what's the mass number when you don't want to know what it is?
5. RAM: weighted average of atomic mass numbers between *isotopes*
Atomic mass number: sum of protons and neutrons
6. (Original post by HN786)
My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
Isn’t that Mr? I’m confused
7. (Original post by HN786)
My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
It’s 1/12 carbon-12
8. (Original post by HN786)
My textbook says don't confuse relative atomic mass Ar, with mass number so whats the difference? I know relative atomic mass is calculated using isotopes and carbon-12. But then whats the mass number?????
The relative atomic mass is the weighted mean mass of all the isotopes of an element relative to one twelfth the mass of the carbon-12 isotope.

The mass number is the number of nucleons (protons and neutrons added together).

There are two common isotopes of chlorine: 35Cl and 37Cl.

Both have the same number of protons (since they are the same element) but different numbers of neutrons, so different mass numbers (35 and 37 respectively).

But they exist in an approximately 3:1 ratio, or 75% of the first and 25% of the second.

So the weighted mean mass, called the relative atomic mass or Ar is calculated as:

g/mol.
9. (Original post by K-Man_PhysCheM)
The relative atomic mass is the weighted mean mass of all the isotopes of an element relative to one twelfth the mass of the carbon-12 isotope.

The mass number is the number of nucleons (protons and neutrons added together).

There are two common isotopes of chlorine: 35Cl and 37Cl.

Both have the same number of protons (since they are the same element) but different numbers of neutrons, so different mass numbers (35 and 37 respectively).

But they exist in an approximately 3:1 ratio, or 75% of the first and 25% of the second.

So the weighted mean mass, called the relative atomic mass or Ar is calculated as:

g/mol.
Thanks
10. i dont wanna confuse u (i could be wrong) but from what i understand mass number changes whereas RAM doesn't--

r.a.m is the AVERAGE mass of all the versions of the atom whereas mass number is just the mass of any one of the versions of the atom.

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