00:01
The mass number of an element is typically a whole number, and that's because it is the total number of protons and neutrons that it has.
00:11
And so if carbon, for example, has six protons and six neutrons, its mass number is 12.
00:19
However, the average atomic mass is typically a decimal.
00:24
And that's because it's an average of the element and isotopes.
00:30
Remember, isotopes have the same number of protons, but the other stuff is not necessarily the same.
00:35
And so about 98 .9 % of carbon has an atomic mass of 12.
00:43
However, there is 1 .1 % that does not.
00:46
It's carbon 13, and it has an atomic mass of 13 .003355.
00:53
And so the way they find this is they multiply our numbers times their percentage.
00:58
And so we have 0 .989, because remember you have to take the percentage and turn it to a decimal, and multiply it by 12...