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Helium is the smallest and the lightest noble gas and one of the most unreactive elements, so it was commonly considered that helium compounds cannot exist at all, or at least under normal conditions. [1] Helium's first ionization energy of 24.57 eV is the highest of any element. [2]
The Sun's photosphere consists mostly of hydrogen and helium; the helium abundance varies between about 10.3 and 10.5 depending on the phase of the solar cycle; [13] carbon is 8.47, neon is 8.29, oxygen is 7.69 [14] and iron is estimated at 7.62.
Under high pressures helium can form compounds with various other elements. Helium-nitrogen clathrate (He(N 2) 11) crystals have been grown at room temperature at pressures ca. 10 GPa in a diamond anvil cell. [130] The insulating electride Na 2 He has been shown to be thermodynamically stable at pressures above 113 GPa. It has a fluorite ...
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]
Coal, in contrast to petroleum, is richer in carbon and poorer in hydrogen. Natural gas is the product of methanogenesis. [13] [14] A seemingly limitless variety of compounds comprise petroleum, hence the necessity of refineries. These hydrocarbons consist of saturated hydrocarbons, aromatic hydrocarbons, or combinations of the two.
The most known chemical elements whose covalent combinations make up most biological molecules on Earth. [2] All of these elements are nonmetals . In animals in general, the four elements—C, H, N, and O—compose about 96% of the weight, and major minerals (macrominerals) and minor minerals (also called trace elements ) compose the remainder.
Without major changes to the Big Bang theory itself, BBN will result in mass abundances of about 75% of hydrogen-1, about 25% helium-4, about 0.01% of deuterium and helium-3, trace amounts (on the order of 10 −10) of lithium, and negligible heavier elements. That the observed abundances in the universe are generally consistent with these ...
Hydrogen is a chemical element; it has symbol H and atomic number 1. It is the lightest element and, at standard conditions, is a gas of diatomic molecules with the formula H 2, sometimes called dihydrogen, [11] hydrogen gas, molecular hydrogen, or simply hydrogen. It is colorless, odorless, [12] non-toxic, and highly combustible.