It is atomic number 81. It has 81 protons and electrons and 123 neutrons. Thallium has a mass of 204.3833 atomic mass units. Its symbol is Tl. It resides in Group IIIA of the periodic table. That is the aluminum family. Thallium has a bluish color after exposure to the air. It is a very soft and malleable metal. It has an electron configuration of 1s22s23s23p64s23d104p65s24d105p64f145d106s26p1. It has 6 electron shells. It melts at 576.7 K and boils at 1730 K. It is a solid when at room temperature.
Thallium was discovered in 1861 by a British chemist and physicist. His name was Sir William Crookes. He discovered it spectroscopically in 
England. He isolated it. In 1862, the French chemist Claude August again isolated it. Thallium comes from the Greek word “thallos”. “Thallos” meant “green twig” or “green shoot”.
Thallium does not have many uses. It is used in photocells because of the electrical conductivity of thallium sulphide. Thallium was originally used to help treat ringworm and many other skin infections. It was then limited because of the narrow margin between the benefits and its health risks. Thallium bromide-iodide crystals are still used as infrared detectors. Thallium sulphate used to be widely used as a pesticide and an ant killer. It was odorless and tasteless and worked well, but it was found to be too toxic. Thallium slats which burn with a bright green flame are used in flares and rockets. Thallium is the 60th most abundant element in the Earth’s crust. There are 3.6 parts of Thallium in every million parts of the Earth’s crust. Thallium compounds are extremely toxic. The negative effects are cumulative and can be taken in through the skin. Poisoning from Thallium takes several days to effect you and when it does, it hits the nervous system. Thallium should only be handled by trained professionals with the right equipment and safety precautions.
Thallium deposits are occasionally found in Sweden and the Former Yugoslav Republic of Macedonia. It is also extracted from the mud produced in lead chambers that are used in the manufacturing of sulfuric acid. Thallium is also used in Thallium high-Tc superconductors. Just recently, Thallium is beginning to be used to visualize the reduced flow of blood into the heart muscle. It is injected into the veins and then a camera records the thallium penetration and shows the areas of the reduced flow of blood.
