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Liquid oxygen is so magnetic that, in laboratory demonstrations, a bridge of liquid oxygen may be supported against its own weight between the poles of a powerful magnet. [37] [c] Singlet oxygen is a name given to several higher-energy species of molecular O 2 in which all the electron spins are paired.
About 99% of the Earth's atmosphere is composed of two species of diatomic molecules: nitrogen (78%) and oxygen (21%). The natural abundance of hydrogen (H 2) in the Earth's atmosphere is only of the order of parts per million, but H 2 is the most abundant diatomic molecule in the universe. The interstellar medium is dominated by hydrogen atoms.
2) is formed when metallic sodium is burned in oxygen. Each oxygen atom in its peroxide ion may have a full octet of 4 pairs of electrons. [6] Superoxides are a class of compounds that are very similar to peroxides, but with just one unpaired electron for each pair of oxygen atoms (O − 2). [6]
Liquid oxygen has a clear cyan color and is strongly paramagnetic: it can be suspended between the poles of a powerful horseshoe magnet. [2] Liquid oxygen has a density of 1.141 kg/L (1.141 g/ml), slightly denser than liquid water, and is cryogenic with a freezing point of 54.36 K (−218.79 °C; −361.82 °F) and a boiling point of 90.19 K (−182.96 °C; −297.33 °F) at 1 bar (14.5 psi).
Carbon forms covalent bonds with other non-metals with an oxidation state of −4, −2, +2 or +4. [25] Carbon is the fourth most abundant element in the universe by mass after hydrogen, helium and oxygen [31] and is the second most abundant element in the human body by mass after oxygen, [32] the third most abundant by number of atoms. [33]
Hydrogen, carbon, oxygen, and nitrogen collectively appeared in most (80%) of compounds. Silicon, a metalloid, ranked 11th. The highest-rated metal, with an occurrence frequency of 0.14%, was iron, in 12th place. [74] A few examples of nonmetal compounds are: boric acid (H 3 BO 3), used in ceramic glazes; [75] selenocysteine (C 3 H 7 NO
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Two or more atoms can combine to form molecules. Some elements are formed from molecules of identical atoms, e. g. atoms of hydrogen (H) form diatomic molecules (H 2). Chemical compounds are substances made of atoms of different elements; they can have molecular or non-molecular structure.