Editing Period 1 element (section)

==Elements==
{| class="wikitable"
|-
! colspan="3" | [[Chemical element]] !! [[Block (periodic table)|Block]] !! [[Electron configuration]]
|- style="background-color: {{element color|s-block}}"
| 1  || '''H'''  || [[Hydrogen]]   || [[s-block]]              || 1s<sup>1</sup>
|- style="background-color: {{element color|s-block}}"
| 2  || '''He''' || [[Helium]]      || [[s-block]]              || 1s<sup>2</sup>
|}

===Hydrogen===
{{Main|Hydrogen}}
[[File:Hydrogen discharge tube.jpg|thumb|150px|Hydrogen discharge tube]]
[[File:Deuterium discharge tube.jpg|thumb|150px|Deuterium discharge tube]]

Hydrogen (H) is the [[chemical element]] with [[atomic number]] 1. At [[standard temperature and pressure]], hydrogen is a colorless, odorless, [[Nonmetal (chemistry)|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&nbsp;amu, hydrogen is the lightest element.<ref>{{cite web|access-date=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 | access-date=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&nbsp;— Production | publisher=Florida Solar Energy Center | access-date=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]]|year=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|title=Electron-Driven Acid-Base Chemistry: Proton Transfer from Hydrogen Chloride to Ammonia|date=2008-02-15|volume=319|issue=5865|pages=936–939|doi=10.1126/science.1151614|author=Eustis, S. N.|journal=Science|pmid=18276886|last2=Radisic|first2=D.|last3=Bowen|first3=K. H.|last4=Bachorz|first4=R. A.|last5=Haranczyk|first5=M.|last6=Schenter|first6=G. K.|last7=Gutowski|first7=M.|bibcode = 2008Sci...319..936E |s2cid=29493053 }}</ref> As the only neutral atom for which the [[Schrödinger equation]] can be solved analytically, study of the energetics and [[atomic spectrum|spectrum]] of the hydrogen atom has played a key role in the development of [[quantum mechanics]].<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|year=2008|title= Time-dependent Schrödinger equation}}</ref>

The interactions 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|bibcode = 1968Sci...159.1057R }}</ref> and in developing safe ways to store it for use as a fuel.<ref>{{cite news | last=Christensen | first=C. H. | author2=Nørskov, J. K. | author3=Johannessen, T. | date=July 9, 2005 | title=Making society independent of fossil fuels&nbsp;— 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 | access-date=2008-03-28 | url-status=dead | archive-url=https://web.archive.org/web/20100107204859/http://www.dtu.dk/English/About_DTU/News.aspx?guid=%7BE6FF7D39-1EDD-41A4-BC9A-20455C2CF1A7%7D | archive-date=January 7, 2010 }}</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. |author2=Wallace, W.E. |author3=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. |author2=Mutschele, T. |author3=Kieninger, W  | title=Hydrogen in amorphous and nanocrystalline metals | journal=Materials Science and Engineering | year=1988 | volume=99 | issue=1–2 | 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}}
[[File:Helium discharge tube.jpg|thumb|upright|150px|Helium discharge tube]]

Helium (He) is a colorless, odorless, tasteless, non-toxic, [[Inert gas|inert]] [[monatomic]] chemical element that heads the [[noble gas]] series in the [[periodic table]] and whose [[atomic number]] is 2.<ref>{{cite web|access-date=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|access-date=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|access-date=2008-07-15|url=http://encarta.msn.com/encyclopedia_762508746/pierre_janssen.html|title=Pierre Janssen|publisher=MSN Encarta|url-status=dead|archive-url=https://web.archive.org/web/20091029133529/http://encarta.msn.com/encyclopedia_762508746/Pierre_Janssen.html|archive-date=2009-10-29}}</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|access-date=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|url-status=dead|archive-url=https://web.archive.org/web/20080725060842/http://www.blm.gov/wo/st/en/info/newsroom/2007/january/NR0701_2.html|archive-date=2008-07-25}}</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=0-387-33324-X}}</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|doi=10.1109/TAU.1966.1161862}}</ref> to cool [[superconducting magnet]]s, in [[helium dating]],<ref>{{cite encyclopedia|encyclopedia=[[Encyclopædia Britannica]]|year=2008|title=helium dating}}</ref> for inflating [[balloon]]s,<ref>{{cite web|access-date=2008-07-15|url=http://www.howstuffworks.com/helium.htm|title=How Helium Balloons Work |publisher=How Stuff Works|author=Brain, Marshall|date=April 2000 }}</ref> for providing lift in [[airship]]s,<ref>{{cite web|access-date=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|access-date=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|access-date=2008-07-15|url=https://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 and is the second most [[chemical abundance|abundant]] in the observable universe.<ref>{{cite web|access-date=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|access-date=2008-07-15|url=https://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]]. This radiogenic helium is trapped with [[natural gas]] in concentrations of up to seven percent by volume,<ref>{{cite web|access-date=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>