Write the formula for terbium(III) fluoride.
Tb3+ with three F-: TbF3 — the standard lanthanide trifluoride pattern, used in specialty glass and phosphor synthesis.
What Is the Charge of Terbium?
Terbium commonly forms Tb3+ Tb4+ in introductory ionic compounds.
Terbium's working charge is Tb3+, the brilliant-green phosphor ion of fluorescent lamps and display screens. Like praseodymium it can be coaxed to +4 in solid oxides (TbO2, Tb4O7), but solution and formula chemistry are +3 territory.
| Element | Terbium |
|---|---|
| Symbol | Tb |
| Atomic number | 65 |
| Common ionic charge | +3, +4 |
| Common ions | Tb3+, Tb4+ |
Visual reference
Terbium element image and atomic model
Images are used as visual references; charge rules still depend on the compound.
The electron story behind Terbium's charge
Terbium is [Xe]4f9 6s2. The conventional +3 gives f8; stripping one more electron reaches the half-filled f7, so a +4 state is within reach in oxide lattices — the mirror image of europium dropping to +2 for the same f7 prize. Everyday chemistry, though, stays at 3+.
This is a classroom reference range, not an exhaustive list of all oxidation states.
The assumption that trips people up on Terbium
Writing terbium's brown air-formed oxide as Tb2O3. Like praseodymium, terbium forms a mixed-valence oxide, Tb4O7 — effectively two Tb3+ and two Tb4+ per formula. The pure sesquioxide Tb2O3 is white and needs controlled preparation.
Worked example: Tb in a formula problem
Tb3+ and Tb4+ in real compounds
TbCl3
Terbium chloride
Tb3+ balances chloride ions.
Tb2O3
Terbium oxide
Terbium can form oxides where total positive and negative charge balances.
Questions students ask about terbium
Where does Tb3+'s green light show up in daily life?
Tri-phosphor fluorescent tubes blend Tb3+ green with Eu3+ red and Eu2+ blue to fake warm white; banknote security inks use the same sharp green emission.
What is Terfenol-D?
A terbium-iron-dysprosium alloy (all neutral atoms) that changes shape in magnetic fields more than any other material — used in precision actuators and underwater sonar. Magnetostriction, not ionic charge, is the trick.
Is terbium's +4 ever useful?
Mostly to chemists studying oxide catalysts and oxygen storage, where the Tb3+/Tb4+ toggle mimics cerium's. Applications overwhelmingly use the luminescent 3+ ion.
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.