Science, Tech, Math › Science Indium Facts: Symbol In or Atomic Number 49 Indium Chemical & Physical Properties Share Flipboard Email Print blueringmedia / Getty Images Science Chemistry Periodic Table Basics Chemical Laws Molecules Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated February 01, 2020 Indium is a chemical element with atomic number 49 and element symbol In. It is a silvery-white metal that most closely resembles tin in appearance. However, it is chemically more similar to gallium and thallium. Except for the alkali metals, indium is the softest metal. Indium Basic Facts Atomic Number: 49 Symbol: In Atomic Weight: 114.818 Discovery: Ferdinand Reich and T. Richter 1863 (Germany) Electron Configuration: [Kr] 5s2 4d10 5p1 Word Origin: Latin indicum. Indium is named for the brilliant indigo line in the element's spectrum. Isotopes: Thirty-nine isotopes of indium are known. They have mass numbers ranging from 97 to 135. Only one stable isotope, In-113, occurs naturally. The other natural isotope is indium-115, which has a half-life of 4.41 x 1014 years. This half-life is much greater than the age of the universe! The reason the half-life is so long is because the beta decay to Sn-115 is spin-forbidden. In-115 accounts for 95.7% of natural indium, with the remainder consisting of In-113. Properties: The melting point of indium is 156.61 °C, boiling point is 2080 °C, specific gravity is 7.31 (20 °C), with a valence of 1, 2, or 3. Indium is a very soft, silvery-white metal. The metal has a brilliant luster and emits a high pitched sound when bent. Indium wets glass. Biological Role: Indium may be toxic, but further research is required to assess its effects. The element serves no known biological function in any organism. Indium(III) salts are known to be toxic to the kidneys. Radioactive In-111 is used as a radiotracer in nuclear medicine to label white blood cells and proteins. Indium is stored in the skin, muscles, and bones, but it is excreted within approximately two weeks. Uses: Indium is used in low melting point alloys, bearing alloys, transistors, thermistors, photoconductors, and rectifiers. When plated or evaporated onto glass, it forms a mirror as good as that formed by silver, but with superior resistance to atmospheric corrosion. Indium is added to dental amalgam to decrease mercury surface tension and aid ease of amalgamation. Indium is used in nuclear control rods. In 2009, indium was combined with manganese and yttrium to form a non-toxic blue pigment, YInMn blue. Indium can be substituted for mercury in alkaline batteries. Indium is considered to be a technology-critical element. Sources: Indium often is associated with zinc materials. It is also found in iron, lead, and copper ores. Indium is the 68th most abundant element in the Earth's crust, present at a concentration of approximately 50 parts per billion. Indium was formed by the s-process in low mass and medium mass stars. The slow neutron capture occurs when silver-109 captures a neutron, becoming silver-110. Silver-110 becomes cadmium-110 by beta decay. Cadmium-110 captures neutrons to become cadmium-115, which undergoes beta decay into cadmium-115. This explains why the radioactive isotope of indium is more common than the stable isotope. Indium-113 is made by the s-process and r-process in stars. It is also a daughter of cadmium-113 decay. The main source of indium is sphalerite, which is a sulfidic zinc ore. Indium is produced as a by-product of ore processing. Element Classification: Metal Indium is a silver-colored metal. AlexLMX / Getty Images Indium Physical Data Density (g/cc): 7.31 Melting Point (K): 429.32 Boiling Point (K): 2353 Appearance: very soft, silvery-white metal Oxidation States: -5, -2, -1, +1, +2, +3 Atomic Radius (pm): 166 Atomic Volume (cc/mol): 15.7 Covalent Radius (pm): 144 Ionic Radius: 81 (+3e) Specific Heat (@20°C J/g mol): 0.234 Fusion Heat (kJ/mol): 3.24 Evaporation Heat (kJ/mol): 225.1 Debye Temperature (K): 129.00 Pauling Negativity Number: 1.78 First Ionizing Energy (kJ/mol): 558.0 Oxidation States: 3 Lattice Structure: Body-centered tetragonal Lattice Constant (Å): 4.590 Sources Alfantazi, A. M.; Moskalyk, R. R. (2003). "Processing of Indium: A Review". 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