Atoms are almost empty
An atom’s mass sits in a tiny nucleus. The rest of its volume is a cloud of electrons; ordinary matter is mostly void.
Established3 min read
Rutherford’s gold-foil experiment (1909–1911) sent alpha particles through metal. Most passed straight. A few ricocheted as if they had hit something hard and small. The nuclear atom replaced the plum pudding.
A hydrogen nucleus is on the order of 10⁻¹⁵ m; the electron cloud is 10⁻¹⁰ m. The volume ratio is a million million to one. Solidity is a feeling produced by Pauli exclusion and electrostatic repulsion, not by packed stuff.
This is why particle beams travel through you, why nuclei can fuse if they get close, and why the table is not a continuum. Chemistry is the physics of those electron clouds.
Caveats
- ‘Empty’ is a classical picture. Quantum fields fill space; the vacuum is not nothing.
- Neutron stars are what matter looks like when the empty part is crushed.
Sources
- 1Rutherford E.. The Scattering of α and β Particles by Matter and the Structure of the Atom. Philosophical Magazine 21, 1911.