00:01
To calculate the average atomic mass of any element, we take the isotopic abundance multiplied by the mass of the isotope.
00:16
However, i like to use the fractional abundance rather than a percent abundance, so i don't need to divide by 100 afterwards.
00:26
So, for example, 1 .37 % is 0 .0137 as a fraction.
00:36
I then multiply that by the isotopic mass at this percent abundance, 203 .0 .97 amu.
00:48
And add to that the fractional abundance of the next isotope, 26 .26%, is 0 .2626 as a fraction.
00:58
We'll multiply that by the mass of its isotope, 205 .97, and then add to that, the fractional abundance of the next isotope, 0 .2082, multiplied by the mass of that isotope, 206.
01:21
0 .98, and then the last isotope at 0 .5 -155, multiplied by its mass, 207 .97 amu.
01:42
And if we keep track of significant figures, this number should have three significant figures.
01:49
It's 2 .7944, last significant figure in the second decimal place.
01:57
This one should have four significant figures.
02:01
It's 54 .0877, last significant figure in the second decimal place...