Editing Chemical element (section)

== Abundance ==
{{Main|Abundance of the chemical elements}}

The following graph (note log scale) shows the abundance of elements in our Solar System. The table shows the 12 most common elements in our galaxy (estimated spectroscopically), as measured in [[parts per million]] by [[mass]].<ref name="croswell">{{cite book |last=Croswell |first=Ken |author-link=Ken Croswell |year=1996 |title=Alchemy of the Heavens |url=http://kencroswell.com/alchemy.html |publisher=Anchor |isbn=978-0-385-47214-2 |access-date=10 October 2007 |archive-date=13 May 2011 |archive-url=https://web.archive.org/web/20110513233910/http://www.kencroswell.com/alchemy.html |url-status=live }}</ref> Nearby galaxies that have evolved along similar lines have a corresponding enrichment of elements heavier than hydrogen and helium. The more distant galaxies are being viewed as they appeared in the past, so their abundances of elements appear closer to the primordial mixture. As physical laws and processes appear common throughout the [[visible universe]], however, scientists expect that these galaxies evolved elements in similar abundance.

The abundance of elements in the Solar System is in keeping with their origin from nucleosynthesis in the [[Big Bang]] and a number of progenitor supernova stars. Very abundant hydrogen and helium are products of the Big Bang, but the next three elements are rare since they had little time to form in the Big Bang and are not made in stars (they are, however, produced in small quantities by the breakup of heavier elements in interstellar dust, as a result of impact by cosmic rays). Beginning with carbon, elements are produced in stars by buildup from alpha particles (helium nuclei), resulting in an alternatingly larger abundance of elements with even atomic numbers (these are also more stable). In general, such elements up to iron are made in large stars in the process of becoming [[supernova]]s. Iron-56 is particularly common, since it is the most stable nuclide that can easily be made from alpha particles (being a product of decay of radioactive nickel-56, ultimately made from 14 helium nuclei). Elements heavier than iron are made in energy-absorbing processes in large stars, and their abundance in the universe (and on Earth) generally decreases with their atomic number.

The [[abundance of the chemical elements]] on Earth varies from air to crust to ocean, and in various types of life. The abundance of elements in Earth's crust differs from that in the Solar System (as seen in the Sun and massive planets like Jupiter) mainly in selective loss of the very lightest elements (hydrogen and helium) and also volatile neon, carbon (as hydrocarbons), nitrogen and sulfur, as a result of solar heating in the early formation of the Solar System. Oxygen, the most abundant Earth element by mass, is retained on Earth by combination with silicon. Aluminium at 8% by mass is more common in the Earth's crust than in the universe and solar system, but the composition of the far more bulky mantle, which has magnesium and iron in place of aluminium (which occurs there only at 2% of mass) more closely mirrors the elemental composition of the solar system, save for the noted loss of volatile elements to space, and loss of iron which has migrated to the Earth's core.

The [[composition of the human body]], by contrast, more closely follows the composition of [[seawater]]—save that the human body has additional stores of carbon and nitrogen necessary to form the [[protein]]s and [[nucleic acid]]s, together with [[phosphorus]] in the nucleic acids and energy transfer molecule [[adenosine triphosphate]] (ATP) that occurs in the cells of all living organisms. Certain kinds of [[organism]]s require particular additional elements, for example the [[magnesium]] in [[chlorophyll]] in green plants, the [[calcium]] in [[mollusc shell]]s, or the iron in the [[hemoglobin]] in [[vertebrate]]s' [[red blood cell]]s.

[[File:SolarSystemAbundances.svg|thumb|upright=2.7|Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, from the Big Bang. The next three elements (Li, Be, B) are rare because they are poorly synthesised in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers (the [[Oddo–Harkins rule]]), and (2) a general decrease in abundance as elements become heavier. Iron is especially common because it represents the minimum energy nuclide that can be made by fusion of helium in supernovae.]]

{|class="wikitable"
|-
!Elements in our galaxy!!Parts per million<br />by mass
|-
|[[Hydrogen]]
|739,000
|-
|[[Helium]]
|240,000
|-
|[[Oxygen]]
|10,400
|-
|[[Carbon]]
|4,600
|-
|[[Neon]]
|1,340
|-
|[[Iron]]
|1,090
|-
|[[Nitrogen]]
|960
|-
|[[Silicon]]
|650
|-
|[[Magnesium]]
|580
|-
|[[Sulfur]]
|440
|-
|[[Potassium]]
|210
|-
|[[Nickel]]
|100
|}
{{clear}}

{{Periodic table (dietary elements)}}