Question

g) Carbon is typically known to consist of 6 protons and 6 neutrons. Then why is the atomic weight of carbon 12.0107 u and not 12.0000 u (assume electrons are weightless)?

Answer 1

Ans :

The carbon atom typically contains 6 protons , 6 neutrons and 6 electrons.

Since the electrons are considered as weightless , the mass of carbon atom is contributed by its neutrons and protons.

The mass of one neutron is 1.008664 u and that of proton is 1.007276 u , but no single atom of carbon has the exact mass of 12.0107 u .

It is the average atomic mass of carbon , since there are different isotopes of carbon (C-12 , C-13 , C-14) found in the nature.

So each isotope multiplied by its natural abundance contributes to the average atomic mass of the carbon atom which is 12.0107 u.