Editing Period 2 element (section)

===Beryllium===
{{main article|Beryllium}}
[[File:Be-140g.jpg|thumb|left|150px|Large piece of beryllium]]

Beryllium (Be) is the chemical element with atomic number 4, occurring in the form of <sup>9</sup>Be. At standard temperature and pressure, beryllium is a strong, steel-grey, light-weight, [[brittle]], [[Bivalent (chemistry)|bivalent]] [[alkaline earth metal]], with a density of 1.85 g⋅cm<sup>−3</sup>.<ref name=webe>[http://www.webelements.com/beryllium/ Beryllium] at WebElements.</ref> It also has one of the highest [[melting point]]s of all the [[light metal]]s. Beryllium's most common [[isotope]] is <sup>9</sup>Be, which contains 4 protons and 5 neutrons. It makes up almost 100% of all naturally occurring beryllium and is its only stable isotope; however [[Isotopes of beryllium|other isotopes]] have been synthesised. In ionic compounds, beryllium loses its two [[valence electron]]s to form the cation, Be<sup>2+</sup>.

Small amounts of beryllium were [[Big Bang nucleosynthesis|synthesised]] during the [[Big Bang]], although most of it [[Nuclear decay|decayed]] or reacted further to create larger nuclei, like carbon, nitrogen or oxygen. Beryllium is a component of 100 out of 4000 known [[mineral]]s, such as [[bertrandite]], Be<sub>4</sub>Si<sub>2</sub>O<sub>7</sub>(OH)<sub>2</sub>, [[beryl]], Al<sub>2</sub>Be<sub>3</sub>Si<sub>6</sub>O<sub>18</sub>, [[chrysoberyl]], Al<sub>2</sub>BeO<sub>4</sub>, and [[phenakite]], Be<sub>2</sub>SiO<sub>4</sub>. Precious forms of beryl are [[Aquamarine (gemstone)|aquamarine]], [[red beryl]] and [[emerald]]. The most common sources of beryllium used commercially are beryl and bertrandite and production of it involves the [[redox|reduction]] of [[beryllium fluoride]] with [[magnesium]] metal or the [[electrolysis]] of molten [[beryllium chloride]], containing some [[sodium chloride]] as beryllium chloride is a poor [[Electrical conductor|conductor of electricity]].<ref name=webe/>

Due to its stiffness, light weight, and dimensional stability over a wide temperature range, beryllium metal is used in as a structural material in aircraft, missiles and [[communication satellite]]s.<ref name=webe/> It is used as an alloying agent in [[beryllium copper]], which is used to make electrical components due to its high electrical and heat conductivity.<ref>[http://www.copper.org/resources/properties/microstructure/be_cu.html Standards and properties] of beryllium copper.</ref> Sheets of beryllium are used in [[X-ray]] detectors to filter out [[visible light]] and let only X-rays through.<ref name=webe/> It is used as a [[neutron moderator]] in [[nuclear reactor]]s because light nuclei are more effective at slowing down neutrons than heavy nuclei.<ref name=webe/> Beryllium's low weight and high rigidity also make it useful in the construction of [[tweeter]]s in [[loudspeaker]]s.<ref>[http://www.hometheaterhifi.com/volume_14_3/feature-article-beryllium-9-2007.html Information] about beryllium tweeters.</ref>

Beryllium and beryllium compounds are classified by the [[International Agency for Research on Cancer]] as [[List of IARC Group 1 carcinogens|Group 1 carcinogens]]; they are carcinogenic to both animals and humans.<ref>{{cite web
 | url = http://www.inchem.org/documents/iarc/vol58/mono58-1.html
 | publisher = International Agency for Research on Cancer
 | title = IARC Monograph, Volume 58
 | year = 1993
 | access-date = 2008-09-18}}</ref> Chronic [[berylliosis]] is a [[pulmonary]] and [[systemic circulation|systemic]] [[granulomatous]] disease caused by exposure to beryllium. Between 1% – 15% of people are sensitive to beryllium and may develop an inflammatory reaction in their [[respiratory system]] and [[skin]], called chronic beryllium disease or [[berylliosis]]. The body's [[immune system]] recognises the beryllium as foreign particles and mounts an attack against them, usually in the lungs where they are breathed in. This can cause fever, fatigue, weakness, night sweats and difficulty in breathing.<ref>[https://web.archive.org/web/20010331191955/http://www.chronicberylliumdisease.com/medical/med_bediseases.htm#cbd Information] about chronic beryllium disease.</ref>