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Where is most of an atomâs mass located?
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subatomic particle
The Large Hadron Collider (LHC), the world's most powerful particle accelerator. At the LHC, located underground in Switzerland, physicists study subatomic particles.
Virtually all of an atomâs mass is concentrated in its nucleus.
While an atom is composed of protons, neutrons, and electrons, the electrons are so lightâapproximately 1/1,836 the mass of a protonâthat they are considered nearly massless in comparison and are not included when calculating an atom's mass number. The nucleus, which sits at the center of the atom, contains the protons and neutrons and accounts for the vast majority of the atom's total mass, despite occupying only a tiny fraction of its total volume.12