The mass of the atomic nucleus is indeed much larger than the mass of the electron cloud, despite occupying a much smaller volume within the atom. This is due to the fundamental differences in the masses of protons and neutrons, which make up the nucleus, compared to electrons.
Protons and neutrons are collectively referred to as nucleons and are significantly more massive than electrons. The mass of a proton is approximately 1,836 times that of an electron, while the mass of a neutron is slightly larger than that of a proton. In comparison, the mass of an electron is relatively small.
The reason why the atomic nucleus accounts for the majority of an atom's mass is primarily because protons and neutrons contribute significantly to the total mass of an atom. The electron cloud, on the other hand, occupies a larger volume but has much less mass compared to the nucleons.
Additionally, the protons in the nucleus carry positive charges, while electrons have negative charges. The positive charge of the protons is balanced by the negative charge of the electrons, resulting in an overall neutral atom. The electron cloud's distribution and its interactions with the positively charged nucleus play a crucial role in determining the atom's chemical and physical properties. However, in terms of mass, the nucleons dominate due to their much larger mass compared to electrons.