Period 1 element
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A '''period 1 element''' is one of the [[chemical element]]s in the first row (or "[[Periodic table period|period]]") of the [[periodic table|periodic table of the chemical elements]]. The periodic table is laid out in rows to illustrate recurring ("periodic") trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The first period contains less elements than any other row in the table, with only two: [[hydrogen]] and [[helium]]. Helium behaves as a [[noble gas]], and is taken as the end of the row; the next period contains eight elements, as it is not until then that another element behaving as a noble gas occurs. This situation can be explained by modern theories of [[atomic structure]].
==Overview==
A period 1 element is one of the chemical elements in the first row (or "period") of the periodic table of the chemical elements. This first period contains less elements than any other row in the table, with only hydrogen and helium. In a [[quantum mechanics|quantum mechanical]] description of [[atom]]ic structure, this period corresponds to the filling of the 1s orbital. Period 1 elements do not obey the [[octet rule]]. The maximum number of electrons that both elements can accommodate is two; an element with a configuration of two elements is called a ''duet''. When hydrogen has two outer, or [[valence]], electrons it is called ''duet happy''.<ref name="bloch2006p7">{{harvnb|Bloch|2006|p=7–8}}</ref>
==Elements==
===Hydrogen===
{{main|Hydrogen}}
Hydrogen (H) is the [[chemical element]] with [[atomic number]] 1. At [[standard temperature and pressure]], hydrogen is a colorless, odorless, [[nonmetal]]lic, tasteless, highly [[combustion|flammable]] [[Diatomic molecule|diatomic]] [[gas]] with the [[molecular formula]] H<sub>2</sub>. With an [[atomic mass]] of 1.00794 amu, hydrogen is the lightest element.<ref>{{cite web|accessdate=2008-07-15|url=http://www.eia.doe.gov/kids/energyfacts/sources/IntermediateHydrogen.html|title=Hydrogen – Energy |publisher=Energy Information Administration }}</ref>
Hydrogen is the most [[abundance of the chemical elements|abundant]] of the chemical elements, constituting roughly 75% of the universe's elemental mass.<ref>{{cite web | last=Palmer | first=David | date=[[November 13]], [[1997]] | url=http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/971113i.html | title=Hydrogen in the Universe | publisher=NASA | accessdate=2008-02-05 }}</ref> [[Star]]s in the [[main sequence]] are mainly composed of hydrogen in its [[plasma (physics)|plasma]] state. Elemental hydrogen is relatively rare on [[Earth]], and is industrially produced from [[hydrocarbon]]s such as methane, after which most elemental hydrogen is used "captively" (meaning locally at the production site), with the largest markets almost equally divided between [[fossil fuel]] upgrading, such as [[hydrocracking]], and [[ammonia]] production, mostly for the fertilizer market. Hydrogen may be produced from water using the process of [[electrolysis]], but this process is significantly more expensive commercially than hydrogen production from natural gas.<ref>{{cite web | author=Staff | year=2007 | url=http://www.fsec.ucf.edu/en/consumer/hydrogen/basics/production.htm | title=Hydrogen Basics — Production | publisher=Florida Solar Energy Center | accessdate=2008-02-05 }}</ref>
The most common naturally occurring [[isotope]] of hydrogen, known as [[hydrogen-1|protium]], has a single [[proton]] and no [[neutron]]s.<ref>{{cite news|title=Fusion Power Is Still Facing Formidable Difficulties|work=The New York Times|date=1971-03-11|author=Sullivan, Walter}}</ref> In [[ionic compound]]s, it can take on either a positive charge, becoming a [[Ion|cation]] composed of a bare proton, or a negative charge, becoming an [[Ion|anion]] known as a [[hydride]]. Hydrogen can form compounds with most elements and is present in [[water]] and most [[organic compound]]s.<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|date=2008|title=hydrogen}}</ref> It plays a particularly important role in [[acid-base reaction theories|acid-base chemistry]], in which many reactions involve the exchange of protons between soluble molecules.<ref>{{cite journal|accessdate=2008-07-15|url=http://www.sciencemag.org/cgi/content/abstract/319/5865/936|title=Electron-Driven Acid-Base Chemistry: Proton Transfer from Hydrogen Chloride to Ammonia |work=Science Magazine|date=2008-02-15|volume=319|issue=5865|pages=936–939|doi=10.1126/science.1151614 }}</ref> As the only neutral atom for which the [[Schrödinger equation]] can be solved analytically, study of the energetics and bonding of the hydrogen atom has played a key role in the development of [[quantum mechanics]].<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|date=2008|title= Time-dependent Schrödinger equation}}</ref>
The [[solubility]] and [[characteristics]] of hydrogen with various metals are very important in [[metallurgy]], as many metals can suffer [[hydrogen embrittlement]],<ref>{{cite journal | last=Rogers | first=H. C. | title=Hydrogen Embrittlement of Metals | journal=Science | year=1999 | volume=159 | issue=3819 | pages=1057–1064 | doi=10.1126/science.159.3819.1057 | pmid=17775040}}</ref> and in developing safe ways to store it for use as a fuel.<ref>{{cite news | last=Christensen | first=C. H. | coauthors=Nørskov, J. K.; Johannessen, T. | date=[[July 9]], [[2005]] | title=Making society independent of fossil fuels — Danish researchers reveal new technology | publisher=Technical University of Denmark | url=http://www.dtu.dk/English/About_DTU/News.aspx?guid=%7BE6FF7D39-1EDD-41A4-BC9A-20455C2CF1A7%7D | accessdate=2008-03-28 }}</ref> Hydrogen is highly soluble in many compounds composed of [[Rare earth element|rare earth metals]] and [[transition metal]]s<ref name="Takeshita">{{cite journal | last=Takeshita | first=T. | coauthors=Wallace, W.E.; Craig, R.S. | title=Hydrogen solubility in 1:5 compounds between yttrium or thorium and nickel or cobalt | journal=Inorganic Chemistry | year=1974 | volume=13 | issue=9 | pages=2282–2283 | doi = 10.1021/ic50139a050 }}</ref> and can be dissolved in both [[crystalline]] and [[amorphous solid|amorphous]] metals.<ref name="Kirchheim1">{{cite journal | last=Kirchheim | first=R. | coauthors=Mutschele, T.; Kieninger, W | title=Hydrogen in amorphous and nanocrystalline metals | journal=Materials Science and Engineering | year=1988 | volume=99 | pages=457–462 | doi = 10.1016/0025-5416(88)90377-1 }}</ref> Hydrogen solubility in metals is influenced by local distortions or impurities in the metal [[crystal lattice]].<ref name="Kirchheim2">{{cite journal | last=Kirchheim | first=R. | title=Hydrogen solubility and diffusivity in defective and amorphous metals | journal=Progress in Materials Science | year=1988 | volume=32 | issue=4 | pages=262–325 | doi = 10.1016/0079-6425(88)90010-2}}</ref>
===Helium===
{{main|Helium}}
Helium (He) is a colorless, odorless, tasteless, non-toxic, [[inert]] [[monatomic]] [[chemical element]] that heads the [[noble gas]] series in the [[periodic table]] and whose [[atomic number]] is 2.<ref>{{cite web|accessdate=2008-07-15|url=http://www.webelements.com/helium/|title=Helium: the essentials |publisher=WebElements }}</ref> Its [[boiling point|boiling]] and [[melting point|melting]] points are the lowest among the elements and it exists only as a [[gas]] except in extreme conditions.<ref>{{cite web|accessdate=2008-07-15|url=http://www.webelements.com/helium/physics.html|title=Helium: physical properties |publisher=WebElements }}</ref>
Helium was discovered in 1868 by French astronomer [[Pierre Janssen]], who [[discovery of the chemical elements|first detected]] the substance as an unknown yellow [[spectroscopy|spectral line]] signature in light from a [[solar eclipse]].<ref>{{cite web|accessdate=2008-07-15|url=http://encarta.msn.com/encyclopedia_762508746/pierre_janssen.html|title=Pierre Janssen |publisher=MSN Encarta }}</ref> In 1903, large reserves of helium were found in the [[natural gas field]]s of the United States, which is by far the largest supplier of the gas.<ref>{{cite web|accessdate=2008-07-15|url=http://www.blm.gov/wo/st/en/info/newsroom/2007/january/NR0701_2.html|title=Where Has All the Helium Gone? |publisher=Bureau of Land Management|date=2007-01-18|author=Theiss, Leslie }}</ref> The substance is used in [[cryogenics]],<ref>{{cite book|title=Cryogenic Engineering: Fifty Years of Progress|author=Timmerhaus, Klaus D.|date=[[2006-10-06]]|publisher=Springer|isbn=038733324X}}</ref> in deep-sea breathing systems,<ref>{{cite journal|title=Helium voice unscrambling|author=Copel, M.|journal=Audio and Electroacoustics|volume=14|issue=3|date=September 1966|pages=122–126}}</ref> to cool [[superconducting magnet]]s, in [[helium dating]],<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|date=2008|title=helium dating}}</ref> for inflating [[balloon]]s,<ref>{{cite web|accessdate=2008-07-15|url=http://www.howstuffworks.com/helium.htm|title=How Helium Balloons Work |publisher=How Stuff Works|author=Brain, Marshall }}</ref> for providing lift in [[airship]]s,<ref>{{cite web|accessdate=2008-07-15|url=http://www.popsci.com/military-aviation-space/article/2008-07/return-blimp|title= The Return of the Blimp |work=Popular Science|date=2008-07-10|author=Jiwatram, Jaya }}</ref> and as a protective gas for industrial uses such as [[arc welding]] and growing [[silicon]] wafers.<ref>{{cite journal|title=When good GTAW arcs drift; drafty conditions are bad for welders and their GTAW arcs.|journal=Welding Design & Fabrication|date=[[2005-02-01]]}}</ref> Inhaling a small [[volume]] of the gas temporarily changes the timbre and quality of the human voice.<ref>{{cite web|accessdate=2008-07-15|url=http://www.sciam.com/article.cfm?id=why-does-inhaling-helium|title=Why does inhaling helium make one's voice sound strange? |work=Scientific American|date=2006-09-04|author=Montgomery, Craig }}</ref> The behavior of liquid helium-4's two fluid phases, helium I and helium II, is important to researchers studying [[quantum mechanics]] and the phenomenon of [[superfluidity]] in particular,<ref>{{cite web|accessdate=2008-07-15|url=http://www.sciencedaily.com/releases/2004/09/040903085531.htm|title=Probable Discovery Of A New, Supersolid, Phase Of Matter |publisher=Science Daily|date=2004-09-03 }}</ref> and to those looking at the effects that temperatures near [[absolute zero]] have on [[matter]], such as with [[superconductivity]].<ref>{{cite news|title=Scientists See Peril In Wasting Helium; Scientists See Peril in Waste of Helium|work=The New York Times|date=1979-08-21|author= Browne, Malcolm W.}}</ref>
Helium is the second lightest element<ref>{{cite web|accessdate=2008-07-15|url=http://www.webelements.com/helium/|title=Helium: the essentials |publisher=WebElements }}</ref> and is the second most [[chemical abundance|abundant]] in the observable universe.<ref>{{cite web|accessdate=2008-07-15|url=http://www.webelements.com/helium/geology.html|title=Helium: geological information |publisher=WebElements }}</ref> Most helium was formed during the [[Big Bang]], but new helium is being created as a result of the [[nuclear fusion]] of hydrogen in [[star]]s.<ref>{{cite web|accessdate=2008-07-15|url=http://www.newscientist.com/article/mg12517027.000-origin-of-the-chemical-elements.html|title=Origin of the chemical elements
|work=New Scientist|date=1990-02-03|author=Cox, Tony}}</ref> On [[Earth]], helium is relatively rare and is created by the natural [[radioactive decay|decay]] of some radioactive elements<ref>{{cite news|title=Helium supply deflated: production shortages mean some industries and partygoers must squeak by.|publisher=Houston Chronicle|date=2006-11-05}}</ref> because the [[alpha particle]]s that are emitted consist of helium [[atomic nucleus|nuclei]].<ref>{{cite news|title=CALL EARTH'S AGE 2 1/2 BILLION YEARS; Wilkins and Rayton Report to Scientists, at Rochester, on Extensive Study. 'INFANCY' A LONG PERIOD Time Before Maturity Into Cold Planet Put at 700,000,000 Through Atomic Method.|work=The New York Times|date=[[1936-06-17]]|author=Laurence, William L.}}</ref> This radiogenic helium is trapped with [[natural gas]] in concentrations of up to seven percent by volume,<ref>{{cite web|accessdate=2008-07-15|url=http://www.aapg.org/explorer/2008/02feb/helium.cfm|title=Helium a New Target in New Mexico |publisher=American Association of Petroleum Geologists|date=2008-02-02|author=Brown, David }}</ref> from which it is extracted commercially by a low-temperature separation process called [[fractional distillation]].<ref>{{cite news|title=Where Do We Get the Helium We Use?|publisher=The Science Teacher|date=2006-12-01|author=Voth, Greg}}</ref>
==Table of elements==
{| align="center" style="text-align:center; width:80%;"
|+ '''Chemical elements in the first period'''
|-
! [[Periodic table group|Group]]
! [[Alkali metal |1]]
! [[Alkaline earth metal|2]]
! [[Group 3 element |3]]
! [[Group 4 element |4]]
! [[Group 5 element |5]]
! [[Group 6 element |6]]
! [[Group 7 element |7]]
! [[Group 8 element |8]]
! [[Group 9 element |9]]
! [[Group 10 element |10]]
! [[Group 11 element |11]] <!-- also [[Coinage metal|11]] -->
! [[Group 12 element |12]]
! [[Boron group |13]]
! [[Carbon group |14]]
! [[Nitrogen group |15]] <!-- also [[Pnictogen|15]] -->
! [[Chalcogen |16]]
! [[Halogen |17]]
! [[Noble gas |18]]
|-
! #<br />Name
| bgcolor="#a0ffa0" |<font color="green">1</font><br />[[Hydrogen|H]]
| colspan="16" |
| bgcolor="#c0ffff" |<font color="green">2</font><br />[[Helium|He]]
|-
! [[electron configuration|e<sup>-</sup>-conf.]]
|}
<center>{{element color legend}}</center>
==Notes==
{{reflist|colwidth=30em}}
==References==
* {{cite book|title=Organic Chemistry Demystified|author=Bloch, D. R.|date=2006|publisher=McGraw-Hill Professional|isbn=0071459200|ref=CITEREFBloch2006|url=http://books.google.com/books?id=yVPcSIn5xjAC}}
{{PeriodicTablesFooter}}
[[Category:Periodic table]]
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[[fr:Éléments de la période 1]]
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