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
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
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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FAQs on Thallium
1. What is thallium and where is it found in the periodic table?
Thallium (symbol Tl) is a soft, greyish, and highly toxic metal. It is located in Group 13 of the periodic table, alongside elements like boron and aluminium. Because of its position, it is classified as a post-transition metal. It is so soft that it can be cut with a knife at room temperature.
2. What are the main uses of thallium?
Although highly toxic, thallium has some specialised industrial and medical uses. It is primarily used in:
- Specialised electronic devices like photocells, which are sensitive to infrared light.
- The manufacturing of low-melting-point glass.
- Medical imaging, specifically in thallium stress tests, where a radioactive isotope is used to examine blood flow to the heart.
- Historically, it was a key ingredient in rodenticides (rat poison), but this use is now banned in most countries due to its extreme danger.
3. What is thallium poisoning and what are its symptoms?
Thallium poisoning is a severe medical emergency caused by ingesting or absorbing the metal. It is particularly dangerous because its compounds are often odourless and tasteless. The symptoms affect many body systems and typically include severe stomach pain, vomiting, diarrhoea, nerve damage, and distinctive hair loss that begins about two to three weeks after exposure.
4. Why does thallium typically show a +1 oxidation state instead of the common +3 for its group?
This unusual behaviour is due to a chemical principle called the 'inert pair effect'. In heavy elements at the bottom of a group, like thallium, the two outermost 's' electrons are held very tightly by the nucleus. This makes them 'inert' or unlikely to be involved in bonding. As a result, thallium finds it easier to lose only its single 'p' electron, forming a stable +1 oxidation state, rather than losing all three valence electrons to form the +3 state seen in lighter elements like aluminium.
5. Is thallium radioactive?
Naturally occurring thallium is generally not radioactive; it is composed of two stable isotopes, Tl-203 and Tl-205. However, several radioactive isotopes of thallium can be created artificially. The most well-known of these is thallium-201, which is the isotope used in medical heart scans.
6. How does thallium's chemical behaviour differ from other elements in Group 13, like aluminium?
Thallium's properties are quite different from aluminium, mainly due to its larger atomic size and the inert pair effect. Key differences include:
- Oxidation State: Aluminium almost exclusively shows a +3 oxidation state in its compounds. Thallium, however, is more stable and common in the +1 oxidation state.
- Toxicity: Aluminium is considered relatively non-toxic, while thallium is extremely poisonous to humans and animals.
- Basicity of Hydroxides: Thallium(I) hydroxide (TlOH) is a strong base, much like sodium hydroxide. In contrast, aluminium hydroxide is amphoteric, meaning it can act as both an acid and a base.
7. What are some common sources of thallium exposure for humans?
Since thallium is rare, exposure usually happens through specific channels rather than general contact. The primary sources include:
- Industrial waste from facilities that manufacture electronics, pharmaceuticals, or special glass.
- Accidental ingestion of old, banned pesticides or rat poisons.
- Living near hazardous waste sites where thallium has been dumped.
- Consuming food grown in contaminated soil, as some plants can absorb thallium.
- Dust from the smelting of other heavy metals like lead and zinc, which can contain thallium as an impurity.
8. If thallium is so toxic, why was it ever used in products like rat poison?
Thallium was used as a rat poison precisely because of its high toxicity. The thallium compounds used, like thallium sulphate, were effective because they were odourless and tasteless. This meant that rodents would eat the poisoned bait without becoming suspicious. It also acted slowly, ensuring the target animal consumed a lethal dose. However, due to the extreme risk of accidental poisoning for humans and pets, its use in such products has been banned in many parts of the world.
9. Who is credited with the discovery of thallium?
The discovery of thallium is attributed to two scientists who were working independently around the same period. In 1861, English chemist Sir William Crookes first identified the element by noticing a unique bright green line in its spectrum. One year later, in 1862, French chemist Claude-Auguste Lamy became the first person to successfully isolate the pure metal itself.
10. Can you get thallium poisoning from everyday foods?
It is extremely unlikely for a person to get thallium poisoning from a normal diet. While certain plants, particularly those in the cabbage family like kale, can absorb thallium from the ground, the concentration in typical soil is far too low to be harmful. A risk would only arise if food was grown in highly contaminated soil, for example, near an old mine or an unregulated industrial waste site.
