Explain the concept of Average Atomic Mass.

Many naturally occurring elements exist as more than one isotope. When we take into account the existence of these isotopes and their relative abundance,the average atomic mass of that element can be computed.
For example,carbon has the following three isotopes with relative abundances and masses as shown against each of them:

Isotope	Relative Abundance $(\%)$	Atomic mass $(\text{amu})$
${}^{12}C$	$98.892$	$12$
${}^{13}C$	$1.108$	$13.00335$
${}^{14}C$	$2 \times 10^{-10}$	$14.00317$

From the above data,the average atomic mass of carbon is calculated as:
$(0.98892)(12 \ u) + (0.01108)(13.00335 \ u) + (2 \times 10^{-12})(14.00317 \ u) = 12.011 \ u$.
Similarly,average atomic masses for other elements can be calculated.