La
Lanthanide
Lanthanum
Z 57A 139mass 138.91
Atomic model
tap a particleEvery nucleon is drawn individually — 57 protons and 82 neutrons packed into the nucleus, with 57 electrons on shells outside.
57+1
Protons
Set the element — change this and it becomes a different atom.
820
Neutrons
Change only these and you get a different isotope of the same element.
57−1
Electrons
Sit outside the nucleus and decide the chemistry, not the element.
Element data
- Nucleons
- 139 (57 p + 82 n)
- Electron shells
- 2 · 8 · 18 · 19 · 8 · 2
- Valence shell
- 2 electrons
- Atomic mass
- 138.91 u
Stability
Lanthanum has no measured radioactive isotope in this lab — its nuclei are stable, so decay must be shown as an illustration.
Open the decay lab