# Numerical value of mole [closed]

Why is the numerical value of a mole of atoms equal to the atomic weight? For example, hydrogen has an atomic weight of 1.008, so 1 mole of hydrogen atoms has a molar mass of 1.008 g/mol. Why?

• please clarify what you meant by "Why is the numerical value of a mole of atoms equal to the atomic weight? ".A mole of any substance has a mass equal to its atomic weight.The numerical value of mole is fixed for any substance and is not equal to its atomic weight. Commented Feb 28, 2016 at 15:21
• Because we decided that 1 mole of C12 weighed 12 grams. The amu is a unit derived from the gram and the number of atoms in a mole. Commented Feb 28, 2016 at 16:30
• Commented Feb 28, 2016 at 19:12

1 mole=6.022*10^23 particles (its not any unit of mass)

atomic mass of atoms are often expressed in a unit called amu.

1 amu=1.6605*10^(-24) gram (more significant figures are there)

mass of 1 hydrogen atom is 1.008 amu

= 1.008*1.6605*10^(-24) = 1.6737*10^(-24) gram

for 1 mole particles

mass =1.6737*10^(-24) * 6.022*10^(23) = 1.0079 g/mol (approximately 1.008)

• @user27301 what is that you expect by evidence?(sometimes it may not be upto my level of knowledge to explain in depth) Commented Feb 28, 2016 at 15:52
• maybe sources, website if you have any Commented Feb 28, 2016 at 15:54
• @user27301 what proof do you want?I mean about which thing?(that is which part of my answer requires proof ) Commented Feb 28, 2016 at 15:56
• @user27301 just multiply those values in calculator and see for yourself. !en.wikipedia.org/wiki/Mole_(unit) Mole is a unit (just like other units) Commented Feb 28, 2016 at 16:01
• The rest of the story - The atomic weight in the periodic table isn't for a single isotope, but for the mix of isotopes typical for that element. So chlorine is 75.77% $\ce{^{35}Cl}$ and 24.23% $\ce{^{37}Cl}$. Overall the mixture of isotopes still has $6.022*10^{23}$ atoms.
– MaxW
Commented Feb 28, 2016 at 17:54