Atoms are 99.9999999% empty space. Solid matter is mostly nothing — held together by forces, not stuff.
An atom's nucleus contains essentially all of its mass but takes up roughly one trillionth of its volume. If an atom were scaled up to the size of a football stadium, the nucleus would be a marble at the 50-yard line. Everything else is empty.
What makes solid matter solid isn't density — it's the electromagnetic forces between atoms. When you push on a table, your atoms aren't touching the table's atoms; their electron clouds are repelling each other.
These verified facts cover atomic structure, isotopes, fundamental particles, and the strange facts that emerge when you zoom in far enough that classical physics stops applying.
Below: every fact from our verified archive that touches this topic. Each is independently sourced; click through to its dedicated page.