The mass number of an element is equal to

We can say that the mass number (A) is the sum of the masses of the particles in an atom, but since the mass of the electron is negligible compared to the masses of protons and neutrons, the mass number is the sum of the masses of protons (Z) and neutrons (n).

number of molecules / avogadro's number * molecule molecular = mass

explanation:

we define a gram-molecular weight as the mass of one mole of any element or compound. a mole contains avogadro's number of units (molecules) –  

6.022

x

10

23

. so, dividing the number of molecules by avogadro's number gives us the number of moles. multiplying that by the molecular weight gives us the mass. from the periodic table we find the gram-molecular weight of u to be238 and of f to be19. so,  

u

f

6

will have a gram-molecular weight of 352g.