Ad
related to: hydrogen and helium combined
Search results
Results from the WOW.Com Content Network
Francis Aston had also recently shown that the mass of a helium atom was about 0.8% less than the mass of the four hydrogen atoms which would, combined, form a helium atom (according to the then-prevailing theory of atomic structure which held atomic weight to be the distinguishing property between elements; work by Henry Moseley and Antonius ...
The proton–proton chain, also commonly referred to as the p–p chain, is one of two known sets of nuclear fusion reactions by which stars convert hydrogen to helium. It dominates in stars with masses less than or equal to that of the Sun , [ 2 ] whereas the CNO cycle , the other known reaction, is suggested by theoretical models to dominate ...
The CNO cycle (for carbon–nitrogen–oxygen; sometimes called Bethe–Weizsäcker cycle after Hans Albrecht Bethe and Carl Friedrich von Weizsäcker) is one of the two known sets of fusion reactions by which stars convert hydrogen to helium, the other being the proton–proton chain reaction (p–p cycle), which is more efficient at the Sun's ...
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.
Once temperatures are lowered, out of every 16 nucleons (2 neutrons and 14 protons), 4 of these (25% of the total particles and total mass) combine quickly into one helium-4 nucleus. This produces one helium for every 12 hydrogens, resulting in a universe that is a little over 8% helium by number of atoms, and 25% helium by mass.
After about 20 minutes, the universe had expanded and cooled to a point at which these high-energy collisions among nucleons ended, so only the fastest and simplest reactions occurred, leaving our universe containing hydrogen and helium. The rest is traces of other elements such as lithium and the hydrogen isotope deuterium. Nucleosynthesis in ...
Helium's first ionization energy of 24.57 eV is the highest of any element. [2] Helium has a complete shell of electrons, and in this form the atom does not readily accept any extra electrons nor join with anything to make covalent compounds. The electron affinity is 0.080 eV, which is very close to zero. [2]
Hydrogen fusion (nuclear fusion of four protons to form a helium-4 nucleus [20]) is the dominant process that generates energy in the cores of main-sequence stars. It is also called "hydrogen burning", which should not be confused with the chemical combustion of hydrogen in an oxidizing atmosphere.
Ad
related to: hydrogen and helium combined