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Why is nearly all of an atom’s mass concentrated in its nucleus?

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Bohr model diagram of a hydrogen atom showing a green nucleus labeled H, a single electron orbit, and text with atomic mass 1.008 and electron configuration 1. — atom The Bohr model describes the structure of atoms, in this case hydrogen.

Nearly all of an atom’s mass is concentrated in its nucleus because the nucleus contains the atom's protons and neutrons, which are significantly more massive than the electrons that surround it.12

While electrons are essential components of an atom, they are the lightest charged particles in nature. A single proton is approximately 1,836 times more massive than an electron, and neutrons are even slightly more massive than protons. Because electrons possess such negligible mass in comparison, they are not included when calculating an atom's mass number. Consequently, the vast majority of an atom's total mass resides within the dense, central nucleus, despite the fact that the nucleus occupies only a tiny fraction of the atom's total volume.2314