The nucleus of an atom contains most of the mass of the atom. This is because the nucleus is composed of protons and neutrons, which have much greater mass compared to electrons.
Protons and neutrons are subatomic particles found within the nucleus of an atom. Protons have a positive charge, while neutrons are electrically neutral. Both protons and neutrons have a mass of approximately 1 atomic mass unit (amu), whereas electrons have a significantly smaller mass, roughly 1/1836 amu.
The mass of an atom is determined by the combined mass of its protons, neutrons, and electrons. However, due to the small mass of electrons relative to protons and neutrons, the mass of the electrons is typically considered negligible when calculating the total mass of an atom. Therefore, the majority of an atom's mass is concentrated in its nucleus, which contains the protons and neutrons.
It is important to note that the mass of a nucleus is slightly less than the sum of the masses of its individual protons and neutrons. This discrepancy is due to the phenomenon of mass defect, which occurs when the binding energy that holds the nucleus together is converted into mass according to Einstein's mass-energy equivalence principle (E=mc^2). The mass defect accounts for the missing mass, and it is converted into the binding energy that keeps the nucleus stable.
In summary, the nucleus of an atom has more mass compared to the electrons because it contains most of the atom's mass, primarily due to the presence of protons and neutrons.