Question

Why is the density of a nucleus much more than that of an atom?

Hint:

Most of the mass of an atom is concentrated in the nucleus, while most of the volume of the atom is empty space.

Answer 1

Step 1: Structure of an atom.
An atom consists of a very small central nucleus surrounded by electrons that move in large orbits around it. The nucleus contains protons and neutrons which together account for almost the entire mass of the atom.

Step 2: Size comparison between atom and nucleus.
The size of a nucleus is extremely small compared to the size of the atom. The radius of an atom is about $10^{-10}\ \text{m}$ whereas the radius of a nucleus is about $10^{-15}\ \text{m}$. Thus the nucleus occupies only a tiny fraction of the total volume of the atom.

Step 3: Distribution of mass in an atom.
Almost the entire mass of an atom is concentrated within the nucleus, while the surrounding region where electrons move contains very little mass but occupies most of the volume of the atom.

Step 4: Effect on density.
Since density is defined as mass divided by volume, the nucleus has a very large density because nearly the whole mass of the atom is packed into an extremely small volume.

Step 5: Conclusion.
Therefore, the density of a nucleus is much greater than that of the atom because the atomic mass is concentrated in a very small nuclear volume while the atom itself occupies a much larger space.