TI Element

Thallium is a chemical element having symbol TI with an atomic number of 81, as found in the periodic table. It is not found freely in nature and is a grey post-transition metal. Thallium resembles tin when it's isolated but discolours when it is exposed to air. William Crookes and Claude-Auguste Lamy independently discovered Thallium in 1861. Approximately there are 81 electrons inside an atom of this element. The respective electronic configuration of Thallium is [Xe] 4f14 5d10 6s2 6p1. This element is not exclusively found or created naturally; rather, it can be created artificially by smelting lead and zinc. Thallium is also produced as a by-product while producing sulphuric acid. 

Here is a Summary of the Relevant Attributes of the Element Thallium



Thallium Symbol




Melting Point of Thallium

304 °C

Thallium Boiling Point

1473° C



Atomic Number


Density at 20°C




Atomic Mass

204.383 g.mol -1


Uses of Thallium

Some of the uses of thallium include:

  • Catalyst during organic reactions

  • For producing optic laser and related equipment

  • Radioisotopes and Mercury Lamps

  • Used in Infra-Red Photocells

  • It is also beneficial in detecting gamma radiation

  • It is also used manufacturing glasses

  • In ancient times, it was found helpful in killing ants and rats.

  • Certain Thallium salts have been used for skin treatments; however, it has more side-effects than benefits because of its highly toxic nature.

Physical Properties of Thallium

Thallium is a malleable metal and looks like Lead (Atomic Number 82) in appearance. Some of its peculiar properties are as follows:

  • It is very soft and melts easily. It can be cut through with a knife and will leave a mark when rubbed on a paper

  • It is heavy and bluish-white in appearance

  • On exhibition to air, it presents a metallic luster as well

  • It is sufficiently abundant

  • Its salts are soluble and usually toxic 

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Chemical Properties of Thallium

A few noteworthy chemical properties of Thallium are:

  • Thallium has a +3 and +1 oxidation state. A +1 oxidation state is although much more stable and shows the chemistry of similarity to alkali metals

  • Thallium reacts with air to create a grey oxide film and when it is heated to enormous amounts it leads to creation of poisonous thallium oxide. The reaction is as follows:

2Tl(s) + O2(g) → Tl2O(s)

  • Thallium reacts steadily with moist air or dissolves in water giving rise to a poisonous material i.e. thallium hydroxide as shown in the following reaction:

2Tl(s) + 2H2O(l) → 2TlOH(aq) + H2(g)

  • Thallium reacts vigorously with the following halogens - Fluorine, Chlorine and Bromine. This leads to origination of these dihalides - thallium fluoride, thallium chloride and thallium bromide. All these are extremely poisonous and their reactions are given below:

2Tl(s) + 3F2(g) → 2TlF3(s) 

2Tl(s) + 3Cl2(g) → 2TlCl3(s) 

2Tl(s) + 3Br2(l) → 2TlBr3(s)

  • Since Thallium is extremely poisonous, it dissolves at a slow speed in only sulphuric acid given as H2SO4 and Hydrochloric Acid given as Hcl.

  • Thallium does not get precipitated by sulfate ions and TI(l) is not precipitated by hydroxide ions. However, TI(lll) precipitates with hydroxide as shown in the  below reaction:

2 Tl3+(aq) + 6 OH(aq) →Tl2O3(s) [brown] + 3 H2O(l)

Structure of Thallium

Having 81 electrons, Thallium has a stable structure, and its atomic data is:  

Atomic Data of Thallium

Atomic Number


Valence Electrons


Noble Gas Configuration

[Xe] 4f145d106s26p1 [1]







Atomic Radius

1.96 Å [1]

Covalent Radius

1.44 Å [1]

Fun Facts

  • The name Thallium comes from a Greek word – Thallos, which means a green twig. This is so connected to this metal as it had a green spectral line.

  • It naturally occurs as a mix of two isotopes. However, today around 25 isotopes of Thallium have been discovered

  • Thallium is suspected to even be carcinogenic. 

  • It can be found as a mineral in elements such as crooksite, lorandite, and hutchinsonite. It was also discovered in iron pyrite, making it another source of Thallium. Ocean floors have manganese nodules, and a small amount of Thallium has been discovered in them as well.

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FAQ (Frequently Asked Questions)

1. What is Thallium Poisoning?

Thallium Poisoning is a critical medical issue and manifests adverse effects on the nervous system and, at the same time, causes vomiting, diarrhea, temporary hair loss, and trouble in the lungs, heart, liver, and kidney. Any exposure to such poisoning can be fatal, and even those who survive face lifelong complications ranging from paralysis to involuntary trembling. An acute after-effect of thallium exposure can be lethargy, coma, hallucinations, and famous Grierson-Gopalan Syndrome. In the Grierson-Gopalan Syndrome, intense burning sensation and itching are felt in the feet, which gave rise to the alternative name of this condition – Burning Feet Syndrome.

Rat Kill poison or such anti-rodent substances are common sources of Thallium Exposure. However, there are some other sources as well:

  • Cigarettes Smoking

  • Working in Thallium using industries or factories

  • Living in areas situated near waste dumping zones storing thallium waste

  • Even contaminated soil may become a source of thallium poisoning.

  • Water that is contaminated with Thallium can also put this mineral inside our bodies, which can further cause intoxication and serious health fatalities.

2. How Was Thallium Discovered?

It is alleged that there is some controversy attached to the origination or finding of Thallium. William Crookes of Royal College of Science, London, observed an intriguing green line in the spectrum of impure sulfuric acid. Later on, he announced it to be a new element in March 1861. A notable point, however, is, Crookes did very limited research over this newly discovered element. Eventually, in 1862, Claude Auguste Lamy of Lille, France, commenced much more thorough research of Thallium and had cast a small ingot of the metal itself. The French Academy credited the discovery to Claude August for that metal.