Hi there!

For calculating atomic mass of an element we add up the no. Of neutrons and protons in an atom of an element .

We do not add no . Of electrons because their mass is considered to be very small…so we add up only neutons and protons

For knowing the no. Of protons … see it's atomic no.

Atomic no. =No.of protons

For knowing the no. Of Neutrons see the periodic table

For eg atomic no. Of oxygen is 8 so 8 are the protons in an atom of Oxygen and the neutrons are 8

So atomic mass=8+8=16

Atomic weight:

Two different quantities are used interchangeably quite a lot of time, Atomic weight and Atomic Mass. But there is a clear cut between both.

Atomic weight is average weight of all the isotopes of an element available in nature whereas Atomic mass is mass of one atom expressed in amu (atomic mass unit).

Now the next question will arise what is one amu. One amu is unit to measure small particles like atoms which cannot be measured in terms of kg , grams, miligrams, micrograms as they are very big units.

One amu is equal to one twelfth of mass of carbon-12 atom or is numerically equal to ( 1.67 × 10 raised to the power of -27) kg.

Thank You.

Hello
harshareddy2422 , The atomic weight of any atom can be found by multiplying the abundance of an isotope of an element by the atomic mass of the element and then adding the results together. This equation can be used with elements with two or more isotopes: Carbon-12: 0.9889 x 12.0000 = 11.8668.

Hope it will be helpful for you :)