00:01
Good day, the topic is about obtaining the average atomic mass of an atom.
00:06
An atom can be composed of several isotopes, which are atoms of the same element having different atomic masses.
00:12
Now, we will get the weighted mass of those isotopes and that will compose our average atomic mass.
00:19
So we say that the average atomic mass is the contribution of the atomic mass of the atoms that make it up.
00:27
So we solve it as the sum of the product of the fraction of abundance of the isotope, that's xi, times the atomic mass of that certain isotope.
00:39
So the fraction of abundance is simply the decimal counterpart of the percentage abundance for that certain isotope.
00:47
So suppose we have silicon atom that is composed mainly of silicon 28, 29, and 30 isotopes, which fraction of abundance are given, and as always, as their atomic mass.
00:59
So note that fraction of abundance as we said is the decimal counterpart of the percentage corresponding to the abundance.
01:07
So this also means that silicon 28 is 92 .2 % of the silicon atom and that silicon 29 is 4 .67 % of the silicon atom.
01:19
Now in this case we wish to find the fraction of abundance or that's translated into percent the percent of abundance of silicon 30 i should as well as its atomic mass.
01:30
So to solve for this we need a data or information on the atomic mass, average atomic mass of silicon.
01:37
So looking up from our reference the atomic mass of a silicon atom is 28 .0855 atomic mass units.
01:46
So we have average atomic mass is equal to 28 .0855 amu.
02:01
For the silicon atom so a atomic mass again is solved as the sum of the product of the atomic or the product of the percent fraction of abundance of the isotope and its corresponding atomic mass so we have for silicon 28 that's going to be 0992 times 27 .9769 and that's going to be 0 .922 times 27 .9769 and that 4 silicon 29 0 .0467 times 28 .97765 and then for silicon 30 we have a times b so this is equal to the average atomic mass which we have already identified or which we set to be equal to 28 .08555 next something that we know about the fraction of abundance or the percent of abundance is that they must sum up to 100%.
03:18
So if we have it as fraction of abundance, then it must equal to 1...