MadSci Network: Chemistry |
Kenneth,
Your were partially correct, but let me fill you in on the rest of
the answer...
The relative atomic mass of any element on the periodic table is just a
sum of how often each isotope occurs in nature times its atomic mass. If
that's a bit confusing, here's an example...
The element chlorine (Cl) is present largely as two different isotopes,
Cl-35 and Cl-37. Cl-35, with a mass of 35, is much more common,
representing about 75% of all naturally existing Chlorine. Cl-37, with
mass of 37, on the other hand, makes up roughly 25% of naturally existing
chlorine. To figure out the relative atomic mass, we just use this
formula:
Relative Atomic Mass = (Isotope 1 occurrence)(Isotope 1 Atomic Mass) +
(Isotope 2 occurrence)(Isotope 2 Atomic Mass) +...
For chlorine, this means:
Relative Atomic Mass = ((75/100)*35) + ((25/100)*37), which equals
35.5.
Of course, there are many more less common isotopes, which cause the
relative atomic mass to actually be around 35.453.
Relative Atomic Mass has no units, since they are all cancelled out
through the calculation!
Check this
website for more information.
Well, hope that helps,
Adil B.
Try the links in the MadSci Library for more information on Chemistry.