The emission spectrum of an element is the frequency spectrum of electromagnetic radiation emitted due to the electrons of a specific atom, creating a transition from a high-energy state to a low energy one. There are many possible electronic transitions for each different atom where the transition has a specific energy difference. The set of different transitions leads to different radiated wavelengths and in turn constitutes an emission spectrum. The emission spectrum of each element is unique and completely different from other elements in the periodic table. To reiterate this statement elements; thallium, neon and iodine will be compared and explained.ThalliumThallium was discovered by Sir William Crookes in 1861, in London. In 1850 Crookes had received a deposit containing selenium from a sulfuric acid factory at Tilkerode. Crookes extracted the selenium and was left with residues that appeared to contain tellurium. Crookes named thallium from the Greek word "thallos" meaning green shoot or twig, in reference to the unique green spectral line that identifies the element in its emission spectra. Thallium possesses properties such as; soft, malleable and not very melting. It is a silvery metal that releases a bluish oxide when heated in air. Its appearance is often misunderstood as that of lead. Thallium can be easily cut using everyday tools (such as a knife) due to its malleability. Once thallium is introduced into water, poisonous thallium hydroxide or TIOH is created. The metal dissolves slowly in hydrochloric acid, dilutes in sulfuric acid, and dissolves rapidly in nitric acid. Thallium sulfate, colorless and odorless, is used in rat poisoning and as an insecticide. This use of that... half of the paper... was done using a spectroscope. Neon is often used in signs for its production of an unmistakable bright red-orange light. Although it is still called "neon", other colors are generated by the variety of noble gases and the various colors of fluorescent lighting. Neon is also used in vacuum tubes, high-voltage indicators, lightning rods, wave meter tubes, television tubes, and helium-neon lasers. When neon is liquefied it is used commercially as a cryogenic refrigerant and the lower temperature range becomes more achievable with extreme refrigeration with liquid helium. For example, neon as both a gas and a liquid is relatively expensive; the price of liquid neon even in small quantities can be more than 55 times that of liquid helium. The reason for the expense of neon is due to its rarity which, unlike helium, can only be obtained from air.