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As a side effect of the process, some carbon nuclei fuse with additional helium to produce a stable isotope of oxygen and energy: 12 6 C + 4 2 He → 16 8 O + γ (+7.162 MeV) Nuclear fusion reactions of helium with hydrogen produces lithium-5, which also is highly unstable, and decays back into smaller nuclei with a half-life of 3.7 × 10 −22 s.
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]
This exothermic reaction is used in the iron and steel industry to smelt iron and to control the carbon content of steel: Fe 3 O 4 + 4 C (s) + 2 O 2 → 3 Fe (s) + 4 CO 2 (g). Carbon reacts with sulfur to form carbon disulfide, and it reacts with steam in the coal-gas reaction used in coal gasification: C (s) + H 2 O (g) → CO (g) + H 2(g).
The order of elements by volume fraction (which is approximately molecular mole fraction) in the atmosphere is nitrogen (78.1%), oxygen (20.9%), [20] argon (0.96%), followed by (in uncertain order) carbon and hydrogen because water vapor and carbon dioxide, which represent most of these two elements in the air, are variable components. Sulfur ...
Helium is the least water-soluble monatomic gas, [96] and one of the least water-soluble of any gas (CF 4, SF 6, and C 4 F 8 have lower mole fraction solubilities: 0.3802, 0.4394, and 0.2372 x 2 /10 −5, respectively, versus helium's 0.70797 x 2 /10 −5), [97] and helium's index of refraction is closer to unity than that of any other gas. [98]
Methane is part of a homologous series known as the alkanes, which contain single bonds only. In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. [1]: 620 Hydrocarbons are examples of group 14 hydrides.
Helium is also used as filling gas in nuclear fuel rods for nuclear reactors. [88] Goodyear Blimp. Since the Hindenburg disaster in 1937, [89] helium has replaced hydrogen as a lifting gas in blimps and balloons: despite an 8.6% [90] decrease in buoyancy compared to hydrogen, helium is not combustible. [13]
[2] [3] Hydrogen also forms compounds with less electronegative elements, such as metals and metalloids, where it takes on a partial negative charge. These compounds are often known as hydrides. [4] Water contains two hydrogen atoms covalently bonded to one oxygen atom, [5] and is one of the most well-studied compounds. [6]