How atomic mass is calculated?

Answer 1

It's the atomic number + the number of neutrons

to find the average atomic mass you must multiply the mass by it's percent natural abundance. do that for each isotope and add your answers together

Answer 2

Atomic Mass is the weighted average of the mass of all forms of that element, compared to 1/12 of an atom of carbon-12.

The 'weighted average' bit is responsible for the decimal places in atomic masses, for example Chlorine, Cl occurs as Cl-35 and Cl-37, with abundances of 75% and 25% respectively, so the atomic mass of Chlorine is 35.5

Answer 3

Atomic mass is calculated by adding the total number of protons and neutrons in an atom's nucleus. The atomic mass is typically measured in atomic mass units (amu) and is found by averaging the mass of all isotopes of an element weighted by their relative abundance. The atomic mass listed on the Periodic Table is the weighted average of all naturally occurring isotopes of an element.