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helium
chemical element
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- Key People:
- Lev Davidovich Landau Sir William Ramsay Heike Kamerlingh Onnes Sir Edward Frankland Sir Joseph Norman Lockyer
- Related Topics:
- air alpha particle helium II helium-4 helium-3
helium (He), chemical element, inert gas of Group 18 (noble gases) of the periodic table. The second lightest element (only hydrogen is lighter), helium is a colourless, odourless, and tasteless gas that becomes liquid at −268.9 °C (−452 °F). The boiling and freezing points of helium are lower than those of any other known substance. Helium is the only element that cannot be solidified by sufficient cooling at normal atmospheric pressure; it is necessary to apply pressure of 25 atmospheres at a temperature of 1 K (−272 °C, or −458 °F) to convert it to its solid form. atomic number2 ...(100 of 1070 words)