Atoms are indeed made up of protons, neutrons, and electrons, but the masses of these subatomic particles are not whole number multiples of the atomic mass unit (amu). The atomic mass unit is defined as one-twelfth the mass of a carbon-12 atom, which is approximately equal to the mass of a proton or a neutron.
Protons and neutrons have masses close to 1 amu, but they are not exact whole numbers. The mass of a proton is approximately 1.0073 amu, while the mass of a neutron is approximately 1.0087 amu.
Electrons, on the other hand, have a much smaller mass compared to protons and neutrons. The mass of an electron is approximately 0.0005486 amu, which is more than 1,800 times lighter than a proton.
When atoms combine to form molecules or other substances, the overall mass of the system is determined by the combined masses of the constituent atoms and their arrangement. The masses of these atoms, including protons, neutrons, and electrons, are not always integer multiples of the atomic mass unit.
So, while atoms are the building blocks of matter, their masses are not necessarily integer multiples of the atomic mass unit.