Question

What is the percentage of the mass of an atom concentrated in the nucleus?

Options

• 99.9 %

• 79.9 %

• 50.9 %

• 66.9 %

Answer 1

99.9 %

Explanation:

The mass of a proton and neutron is around 2000 times that of an electron. In a stable atom (not an isotope), the number of electrons is equal to the number of electrons. As a result, the nucleus of most atoms will have around 4000 times the mass of its electron cloud. Thus,${\displaystyle \frac{{\text{m}}_{\text{nucleus}}}{{\text{m}}_{\text{atom}}}=\frac{4000}{4001}\times 100\%\approx 99.9\%}$