Thallium(I) iodide and thallium(III) iodide differ in a subtle way: TlI 3 is actually thallium(I) triiodide rather than thallium(III) iodide. This is best explained by the fact that:

Tl 3+ is much more stable than Tl + and cannot oxidise iodide ions in dilute solution

Thallium does not form any iodide

Thallium(I) iodide and thallium(III)…

Answer: Tl 3+ is a strong enough oxidant to oxidise I - , so the stable species is Tl + with I 3 -.

A Iodine cannot exist as I3-
B Tl3+ is a strong enough oxidant to oxidise I-, so the stable species is Tl+ with I3-
C Tl3+ is much more stable than Tl+ and cannot oxidise iodide ions in dilute solution
D Thallium does not form any iodide

Correct answer: B. Tl3+ is a strong enough oxidant to oxidise I-, so the stable species is Tl+ with I3-

Explanation: Because of the inert pair effect Tl3+ is a strong oxidiser; it would oxidise I- to iodine, so the compound exists as Tl+(I3)-, i.e., thallium(I) triiodide.

Diamond's rigid 3D tetrahedral network makes it the hardest natural material, while graphite's flat hexagonal sheets are held together only by weak forces, letting them slide past each other (used as a lubricant and in pencils).

Concept context

Covers the Boron family (Group 13: B, Al) and the Carbon family (Group 14: C, Si, Ge, Sn, Pb). Key topics include Lewis acid behaviour of BF₃, borax bead test, silicates, silicones, allotropes of carbon, and trends in properties down the group.

Read the full p-Block Elements (Groups 13 & 14) notes →

Thallium(I) iodide and thallium(III) iodide differ in a subtle way: TlI<sub>3</sub> is actually thallium(I) triiodide rather than thallium(III) iodide. This is best explained by the fact that:

Concept context

More p-Block Elements (Groups 13 & 14) questions