![]() More abundant helium-3 is thought to exist on the Moon. Helium-3 is rare on Earth and sought-after for use in nuclear fusion research. Heavier elements were mostly produced much later, inside stars. The abundance of the lightest elements is well predicted by the standard cosmological model, since they were mostly produced shortly after the Big Bang, in a process known as Big Bang nucleosynthesis. All others are orders of magnitude less common. However, after this, the rank of abundance does not continue to correspond to the atomic number oxygen has abundance rank 3, but atomic number 8. ![]() Hydrogen is the most abundant element in the known Universe helium is second. Standard matter also exists as photons (mostly in the cosmic microwave background) and neutrons. Other forms of baryonic matter include white dwarves, neutron stars and black holes. Most standard (baryonic) matter is found in the form of atoms, although there are many other unusual kinds of matter, mostly plasma. Dark matter has not yet been detected in a particle physics detector, and the nature of the dark energy is not yet understood. Cosmological observations suggest that about 73% of the universe consists of dark energy, 23% is composed of dark matter and only 4% corresponds to the visible baryonic matter which constitutes stars, planets and living beings. The elements - namely ordinary ( baryonic) matter made out of protons and neutrons (as well as electrons) - are only a small part of the content of the Universe. 2.1 Abundance of elements in Earth's crust.1 Abundance of elements in the Universe.Most abundances in this article are given as mass-fraction abundances. However, since hydrogen is diatomic while helium is not in the conditions of Jupiter's outer atmosphere, the molecular mole-fraction (fraction of total gas molecules, or fraction of atmosphere by volume) of hydrogen in the outer atmosphere of Jupiter is about 86%, and for helium, 13%. In the universe as a whole, and in the atmospheres of gas-giant planets such as Jupiter, the mass-fraction abundances of hydrogen and helium are about 74% and 23-25% respectively, while the (atomic) mole-fractions of these elements are closer to 92% and 8%. However, the mole-fraction abundance of oxygen in water is only 33% because only 1 atom in 3 in water is an oxygen atom. ![]() Measurement by volume-fraction is a common abundance measure in mixed gases such as atmospheres, which is close to molecular mole-fraction for ideal gas mixtures (i.e., gas mixtures at relatively low densities and pressures).įor example, the mass-fraction abundance of oxygen in water is about 89%, because that is the fraction of water's mass which is oxygen. Abundance may be variously measured by the mass-fraction (the same as weight fraction), or mole-fraction (fraction of atoms, or sometimes fraction of molecules, in gases), or by volume fraction. The abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. ![]()
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