Predict the formula of thulium(III) oxide.
Tm3+ with O2- gives Tm2O3 — the compound irradiated to make Tm-170 for portable radiography units that X-ray pipelines far from any power supply.
What Is the Charge of Thulium?
Thulium commonly forms Tm3+ in introductory ionic compounds.
Thulium is Tm3+ — pale-green salts like TmCl3 — with a fleeting Tm2+ known mostly to specialists. The rarest stable lanthanide, it follows the +3 rule without drama; its niche fame is in portable X-ray sources and surgical fiber lasers.
| Element | Thulium |
|---|---|
| Symbol | Tm |
| Atomic number | 69 |
| Common ionic charge | +3 |
| Common ions | Tm3+ |
Visual reference
Thulium element image and atomic model
Images are used as visual references; charge rules still depend on the compound.
The electron story behind Thulium's charge
Thulium is [Xe]4f13 6s2. Losing three electrons gives Tm3+ (f12); a 2+ state (f13, one short of full) exists in exotic halides but reduces water on contact. As with most late lanthanides, the +3 hydration and lattice payoffs settle the argument.
This is a classroom reference range, not an exhaustive list of all oxidation states.
The assumption that trips people up on Thulium
Confusing element rarity with charge complexity. Thulium costs more than platinum in pure form, yet a student can predict every one of its formulas from '+3': Tm2O3, TmF3, Tm2(SO4)3. Scarcity is economics, not chemistry.
Worked example: Tm in a formula problem
Tm3+ in real compounds
TmCl3
Thulium chloride
Tm3+ balances chloride ions.
Tm2O3
Thulium oxide
Thulium can form oxides where total positive and negative charge balances.
Questions students ask about thulium
What do thulium fiber lasers do better than holmium's?
Tm3+ lases near 1.94 µm with high efficiency and fine control; urology is shifting stone procedures toward thulium-fiber for smoother cutting at lower energy per pulse.
Why was thulium the last stable lanthanide discovered in quantity?
Nature simply made the least of it (odd atomic number, low cosmic abundance), and its 3+ ion hides among fourteen near-identical siblings. Chemistry offered no handle; only ion-exchange separation finally did.
Does thulium appear in euro banknote inks too?
Blue-emitting Tm3+ complexes are among the luminescent taggants reported in security applications — its sharp f-line emission is difficult to mimic with dyes.
How do I use this charge in formulas?
Combine positive and negative ions so the total charge is zero — or let the ionic compound calculator do the crossing for you. The full chart lives on the periodic table with charges.
Where this data comes from
Charges and element facts on this page are checked against the primary references below. Found an error? Email hello@periodictablewithcharges.com — corrections ship in the next content update. See how this site is edited.