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  1. Helium
    HeliumChemical element
    OverviewDiscoveryPropertiesApplicationsFacts
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    All images
    Appearancecolorless gas, exhibiting a gray, cloudy glow (or reddish-orange if an especially high voltage is used) when placed in an electric field
    Phase at STPgas
    Wikipedia
    https://en.wikipedia.org › wiki › Helium

    Helium - Wikipedia

    History

    The first evidence of helium was observed on August 18, 1868, as a bright yellow line with a wavelength of 587.49 nanometers in the spectrum of the chromosphere of the Sun. The line was detected by French astronomer … See more

    Characteristics

    In the perspective of quantum mechanics, helium is the second simplest atom to model, following the hydrogen atom. Helium is composed of two electrons in atomic orbitals surrounding a nucleus containing two proton… See more

    Compounds

    Helium has a valence of zero and is chemically unreactive under all normal conditions. It is an electrical insulator unless ionized. As with the other noble gases, helium has metastable energy levels that allow i… See more

    Occurrence and production

    Although it is rare on Earth, helium is the second most abundant element in the known Universe, constituting 23% of its baryonic mass. Only hydrogen is more abundant. The vast majority of helium was formed by … See more

    Applications

    While balloons are perhaps the best-known use of helium, they are a minor part of all helium use. Helium is used for many purposes that require some of its unique properties, such as its low boiling point, low density, … See more

    As a contaminant

    While chemically inert, helium contamination impairs the operation of microelectromechanical systems (MEMS) such that iPhones may fail. See more

    Inhalation and safety

    Neutral helium at standard conditions is non-toxic, plays no biological role and is found in trace amounts in human blood.
    The speed of sound in helium is nearly three times the speed of sound in air. Because the … See more

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