| Atom | |
|---|---|
 An illustration of the helium atom, depicting the nucleus (pink) and the electron cloud distribution (black). The nucleus (upper right) in helium-4 is in reality spherically symmetric and closely resembles the electron cloud, although for more complicated nuclei this is not always the case. The black bar is one angstrom (10−10 m or 100 pm). | |
| Classification | |
| Smallest recognized division of a chemical element | |
| Properties | |
| Mass range | 1.67×10−27 to 4.52×10−25 kg |
| Electric charge | zero (neutral), or ion charge |
| Diameter range | 62 pm (He) to 520 pm (Cs) (data page) |
| Components | Electrons and a compact nucleus of protons and neutrons |