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  2. Hydrogen - Wikipedia

    en.wikipedia.org/wiki/Hydrogen

    It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H 2, sometimes called dihydrogen, [11] but more commonly called hydrogen gas, molecular hydrogen or simply hydrogen. It is colorless, odorless, [12] non-toxic, and highly combustible.

  3. Noble gas - Wikipedia

    en.wikipedia.org/wiki/Noble_gas

    Noble gases can form endohedral fullerene compounds, in which the noble gas atom is trapped inside a fullerene molecule. In 1993, it was discovered that when C 60, a spherical molecule consisting of 60 carbon atoms, is exposed to noble gases at high pressure, complexes such as He@C 60 can be formed (the @ notation indicates He is contained inside C

  4. Noble gas compound - Wikipedia

    en.wikipedia.org/wiki/Noble_gas_compound

    Structure of a noble-gas atom caged within a buckminsterfullerene (C 60) molecule. Noble gases can also form endohedral fullerene compounds where the noble gas atom is trapped inside a fullerene molecule. In 1993, it was discovered that when C 60 is exposed to a pressure of around 3 bar of He or Ne, the complexes He@C 60 and Ne@C 60 are formed ...

  5. Diatomic molecule - Wikipedia

    en.wikipedia.org/wiki/Diatomic_molecule

    The noble gases (helium, neon, argon, krypton, xenon, and radon) are also gases at STP, but they are monatomic. The homonuclear diatomic gases and noble gases together are called "elemental gases" or "molecular gases", to distinguish them from other gases that are chemical compounds. [2]

  6. Electron configuration - Wikipedia

    en.wikipedia.org/wiki/Electron_configuration

    Noble gas configuration is the electron configuration of noble gases. The basis of all chemical reactions is the tendency of chemical elements to acquire stability . Main-group atoms generally obey the octet rule , while transition metals generally obey the 18-electron rule .

  7. Period (periodic table) - Wikipedia

    en.wikipedia.org/wiki/Period_(periodic_table)

    Hydrogen readily loses and gains an electron, and so behaves chemically as both a group 1 and a group 17 element. Hydrogen (H) is the most abundant of the chemical elements, constituting roughly 75% of the universe's elemental mass. [1] Ionized hydrogen is just a proton. Stars in the main sequence are mainly composed of hydrogen in its plasma ...

  8. Atomicity (chemistry) - Wikipedia

    en.wikipedia.org/wiki/Atomicity_(chemistry)

    Atomicity is the total number of atoms present in a molecule of an element. For example, each molecule of oxygen (O 2) is composed of two oxygen atoms. Therefore, the atomicity of oxygen is 2. [1] In older contexts, atomicity is sometimes equivalent to valency. Some authors also use the term to refer to the maximum number of valencies observed ...

  9. Properties of nonmetals (and metalloids) by group - Wikipedia

    en.wikipedia.org/wiki/Properties_of_nonmetals...

    Hydrogen in an electrical discharge tube. Hydrogen is a colourless, odourless, and comparatively unreactive diatomic gas with a density of 8.988 × 10 −5 g/cm 3 and is about 14 times lighter than air. It condenses to a colourless liquid −252.879 °C and freezes into an ice- or snow-like solid at −259.16 °C.