Question

How is mass number calculated for an element

Answer 1

The symbolic representation of an element is as follows :

               A 
                   X
              Z
where A is the mass number which is equal to number of protons and neutrons

Z--- is the atomic number which is equal to number of protons.


For example :

To find the mass number of Mg .
Mg has atomic number 12
Z=12=number of protons =number of electrons as atom is electrically neutral.
Mass Number A
A=Z+ Number of neutrons.
Number of neutrons in Magnesium is 12
[Use periodic table to find number of neutrons. ]
A=12+12
So mass number of Mg is 24