Unsur periode 1: Perbedaan antara revisi

[[Hidrogen]] kadang-kadang diletakkan di atas [[litium]],<ref name="iupac" /> di atas [[karbon]],<ref name="hydrogen">{{cite journal |last = Cronyn|first = Marshall W.|title = The Proper Place for Hydrogen in the Periodic Table|journal = Journal of Chemical Education|volume = 80|issue = 8|date = August 2003|pages = 947–951|doi = 10.1021/ed080p947|bibcode = 2003JChEd..80..947C}}</ref> di atas [[fluor]],<ref name="hydrogen" /><ref name="hydrogen-halogen">{{cite web |url = http://hydrogentwo.com/hydrogen-halogen.html|title = Hydrogen is a Halogen|author = Vinson, Greg|year = 2008|work = HydrogenTwo.com|publisher = |accessdate = January 14, 2012|archive-date = 2012-01-10|archive-url = https://web.archive.org/web/20120110195815/http://hydrogentwo.com/hydrogen-halogen.html|dead-url = yes}}</ref> di atas litium dan fluor sekaligus (muncul dua kali),<ref name="chemistry-international" /> atau di kiri mengambang di atas unsur-unsur lainnya dan tidak dimasukkan ke dalam golongan manapun<ref name="chemistry-international">{{cite journal |last1 = Kaesz|first1 = Herb|last2 = Atkins|first2 = Peter|date = November–December 2003|title = A Central Position for Hydrogen in the Periodic Table|journal = Chemistry International|volume = 25|issue = 6|pages = 14|publisher = [[International Union of Pure and Applied Chemistry]]|url = http://www.iupac.org/publications/ci/2003/2506/ud.html|accessdate = January 19, 2012}}</ref> dalam [[tabel periodik]].

Helium pertama kali ditemukan pada tahun 1868 oleh astronom Prancis [[Pierre Janssen]], yang [[Penemuan unsur kimia|pertama kali]] mendeteksi zat sebagai tanda [[Spektroskopi|garis spektrum]] kuning tak diketahui dalam cahaya dari [[gerhana matahari]].<ref>{{cite web|accessdate = 2008-07-15|url = http://encarta.msn.com/encyclopedia_762508746/pierre_janssen.html|title = Pierre Janssen|publisher = MSN Encarta|archive-date = 2009-10-29|archive-url = https://web.archive.org/web/20091029133529/http://encarta.msn.com/encyclopedia_762508746/Pierre_Janssen.html|dead-url = yes}}</ref> Pada tahun 1903, cadangan helium yang besar ditemukan dalam [[ladang gas alam]] di Amerika Serikat, yang dikenal sebagai pemasok gas terbesar.<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|archive-date = 2008-07-25|archive-url = https://web.archive.org/web/20080725060842/http://www.blm.gov/wo/st/en/info/newsroom/2007/january/NR0701_2.html|dead-url = yes}}</ref> Helium digunakan dalam [[kriogenik]],<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> sistem pernapasan laut-dalam<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>, untuk mendinginkan [[Magnet superkonduksi|magnet superkonduktor]], dan dalam [[Penanggalan Helium|penanggalan helium]],<ref>{{cite encyclopedia|encyclopedia = [[Encyclopædia Britannica]]|year = 2008|title = helium dating}}</ref> untuk pengisi [[balon]] udara,<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>, sebagai pengangkat [[kapal udara]],<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> dan sebagai gas pelindung untuk penggunaan industri seperti [[Arc welding|pengelasan]] dan pengembangan wafer [[silikon]].<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> Menghirup [[Volume|sedikit]] gas ini akan mengubah sementara timbre dan kualitas suara manusia.<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> Perilaku fasa dua fluida helium-4 cair, helium I dan helium II, penting bagi peneliti yang mempelajari [[mekanika kuantum]] dan terutama fenomena [[superfluiditas]],<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> dan hal tersebut tampak pada efek bahwa pada temperatur hampir [[nol mutlak]], materi mengalami [[superkonduktivitas]].<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>