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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]
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]
The length of the carbonhydrogen bond varies slightly with the hybridisation of the carbon atom. A bond between a hydrogen atom and an sp 2 hybridised carbon atom is about 0.6% shorter than between hydrogen and sp 3 hybridised carbon. A bond between hydrogen and sp hybridised carbon is shorter still, about 3% shorter than sp 3 C-H.
The valence is the combining capacity of an atom of a given element, determined by the number of hydrogen atoms that it combines with. In methane, carbon has a valence of 4; in ammonia, nitrogen has a valence of 3; in water, oxygen has a valence of 2; and in hydrogen chloride, chlorine has a valence of 1. Chlorine, as it has a valence of one ...
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 ...
They are composed entirely of single bonds and are saturated with hydrogen. The formula for acyclic saturated hydrocarbons (i.e., alkanes) is C n H 2n+2. [1]: 623 The most general form of saturated hydrocarbons, (whether linear or branched species, and whether with or without one or more rings) is C n H 2n+2(1-r), where r is the
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] but more commonly called hydrogen gas, molecular hydrogen or simply hydrogen.
The number of organic compounds is immense and the known number of defined compounds is close to 10 million. [4] However, an indefinitely large number of such compounds is theoretically possible. By definition, an organic compound must contain at least one atom of carbon, but this criterion is not generally regarded as sufficient.