Why does the periodic table present the average atomic mass of an element instead of just one isotope?

Answer 1

For the simple reason that the most common isotope doesn't make up 100% of the element. If you use just that mass, your calculations will be off by anywhere from 0.5% to 3%. That doesn't sound like much, but when you are dealing with huge commodities of dangerous chemicals that need to be in the exactly specified mix or creating drugs that require a precise value of medication to prevent under- or overdosage, you had better be closer than 0.5%.

Answer 2

because there are elements which have isotopes with different atomic masses so it is very confusing so scientists make the average Atomic Mass which we can calculate it by

the isotopic abundance x mass of it in gram + the isotopic abundance of the other isotope x mass of it in gram

I hope i had helped

Answer 3

The atomic mass of an element is the numerical average of all the masses of the naturally occurring isotopes of that element proportionately. Man made elements do not count in supposedly.

IE: If we have an element with atomic weight 100 and we have an isotope of that element with atomic weight 102 and if they occurred equally in nature then the atomic mass would be 101.

Answer 4

... because those elements (eg. chlorine) are natural mixtures of isotopes with the same proton number (= atom number, 17Cl) but different number of neutrons (Cl-35 and Cl-37, with 18 and 20 neutrons respectively). They can't be easily separated, at least not chemically, because they are chemically identical, but their mass differs 2 a.m.u.

Answer 5

The average atomic mass is used so that stoichiometric calculations will be correct for practical problems with "real world" materials that arise frequently in chemical engineering.

Answer 6

Because all of the isotopes are present, not just the most commonly occurring one, and you need to account for that when you do stoichiometric analysis.