Tl
Post-transition metal
Thallium
Z 81A 204mass 204.38
Atomic model
tap a particleEvery nucleon is drawn individually — 81 protons and 123 neutrons packed into the nucleus, with 81 electrons on shells outside.
81+1
Protons
Set the element — change this and it becomes a different atom.
1230
Neutrons
Change only these and you get a different isotope of the same element.
81−1
Electrons
Sit outside the nucleus and decide the chemistry, not the element.
Element data
- Nucleons
- 204 (81 p + 123 n)
- Electron shells
- 2 · 8 · 18 · 32 · 18 · 3
- Valence shell
- 3 electrons
- Atomic mass
- 204.38 u
Stability
Thallium has no measured radioactive isotope in this lab — its nuclei are stable, so decay must be shown as an illustration.
Open the decay lab