Thallium

Thallium belongs to Boron family( Group 13) of the periodic table, also known as the aluminium family—the periodic table organises chemical elements based on their relationships with one another. Thallium is also classified as a heavy metal, similar to elements like gold, platinum, and lead.

Thallium is a chemical element with the symbol Tl and an atomic number 81 on the periodic table. It is not found in its free form in nature and is classified as a grey post-transition metal. When isolated, thallium resembles tin, but it discolours upon exposure to air. Thallium was discovered independently by William Crookes and Claude-Auguste Lamy in 1861. Each element produces a unique series of coloured lines called a spectrum. Thallium’s spectrum is characterised by bright green lines, which is how it got its name. The name "thallium" comes from the Greek word thallos, meaning "green twig," due to the appearance of the green lines resembling green twigs in its spectrum.

Thallium is not exclusively found in nature but artificially produced through lead and zinc smelting. It is also generated as a by-product in the production of sulfuric acid.

1.0Physical Properties of Thallium

2.0Chemical Properties of Thallium

1. Oxidation States: Thallium exhibits two primary oxidation states: +3 and +1. The +1 oxidation state is more stable and resembles the chemistry of alkali metals.
2. Reaction with Air:

Thallium reacts with air, forming a grey oxide film. When heated to high temperatures, it produces toxic thallium oxide (Tl₂O), as shown in the reaction:

2Tl(s)+O₂(g)→Tl₂O(s)

3. Reaction with Water:

Thallium reacts steadily with moist air or dissolves in water, producing poisonous thallium hydroxide (TlOH) and hydrogen gas:

2Tl(s)+2H₂O(l)→2TlOH(aq)+H₂(g)

4. Reaction with Halogens:

Thallium reacts vigorously with halogens such as fluorine, chlorine, and bromine, forming toxic dihalides like thallium fluoride, thallium chloride, and thallium bromide:

• Fluorine: 2Tl(s) + 3F₂(g) → 2TlF₃(s)
• Chlorine: 2Tl(s) + 3Cl₂(g) → 2TlCl₃(s)
• Bromine: 2Tl(s) + 3Br₂(l) → 2TlBr₃(s)

5. Reactivity with Acids:

Thallium dissolves slowly in sulfuric acid (H₂SO₄) and hydrochloric acid (HCl). However, thallium is not precipitated by sulfate ions (SO₄²⁻), and Tl(I) is not precipitated by hydroxide ions (OH⁻).

6. Precipitation of Thallium(III): 

Thallium(III) ions (Tl³⁺) can precipitate with hydroxide ions to form brown thallium oxide (Tl₂O₃​):  

• 2Tl³⁺(aq) + 6^OH−(aq) → Tl₂O₃(s) + 3H₂O(l)

3.0Uses of Thallium

• Catalyst: Thallium is used as a catalyst in various organic reactions.
• Optical Equipment: It plays a role in producing optical lasers and related equipment.
• Radioisotopes and Lighting: Thallium is used to produce radioisotopes and mercury lamps.
• Infrared Photocells: Thallium is employed in infrared photocells because of its unique properties.
• Gamma Radiation Detection: It plays a key role in detecting gamma radiation.
• Glass Manufacturing: Thallium is used to manufacture specialised types of glass.

4.0Effects of Thallium

• Absorption by the Human Body: Thallium is readily absorbed through the skin, respiratory system, and digestive tract, making it particularly dangerous upon exposure.
• Source of Poisoning: Thallium sulfate, often found in rat poison, is a major cause of thallium poisoning.
• Chronic Health Effects: Prolonged exposure to thallium can lead to symptoms such as fatigue, headaches, depression, loss of appetite, leg pain, hair loss, and vision problems.
• Impact on Plants: Thallium affects plants by causing leaf discolouration and inhibiting growth.
• Effect on Animals: Similar to humans, animals, including rabbits, are highly susceptible to the toxic effects of thallium.