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I know , Average Atomic Mass of an element is - the sum of the Masses of its isotopes,each multiplied by its Relative Abundance percentage (in decimal notation).
But what confusing me is, what is the concept of Average Atomic Mass. In other words,why we want to take average atomic mass of every element on the periodic table,why not Atomic mass ? Why we need it and when to use it?
The average atomic mass is useful because its numerical value is equal to the molar mass of the element. This in turn is useful to know how much of a solid to take when you wish to react it with some known quantity of another reagent, because weighing is typically the easiest way to quantify a substance.
If you know precisely which isotope of the element you sre dealing with then go right ahead and use the molecular mass but generally we dont know which isotope is available to us and moreover there are mamy impurities a single gram might have a mixture of kany isotopes. So for reducing the error to the maximum limit possible statistically we multiply the mass of that particular isotope with its relative percentage abundance, you can imagine this as if a particular molecular mass is more available in nature than its more probable that is the isotope we have or that isotope is more in abundance in our mixture and hence the value of the average molecular mass we are using as simplification should tend more to that isotope
