Editing Period 6 element (section)

==p-block elements==

===Thallium===
{{main|Thallium}}
'''Thallium''' is a chemical element with the symbol '''Tl''' and atomic number 81. This soft gray [[other metal]] resembles [[tin]] but discolors when exposed to air. The two chemists [[William Crookes]] and [[Claude-Auguste Lamy]] discovered thallium independently in 1861 by the newly developed method of [[Atomic emission spectroscopy#Flame emission spectroscopy|flame spectroscopy]]. Both discovered the new element in residues of [[sulfuric acid]] production.

Approximately 60–70% of thallium production is used in the [[electronics industry]], and the remainder is used in the [[pharmaceutical industry]] and in [[glass|glass manufacturing]].<ref name="sl2001">{{cite web|title=Chemical fact sheet&nbsp;— Thallium|publisher=Spectrum Laboratories|date=April 2001|url=http://www.speclab.com/elements/thallium.htm|access-date=2008-02-02|archive-url=https://web.archive.org/web/20080221222321/http://www.speclab.com/elements/thallium.htm|archive-date=2008-02-21|url-status=dead}}</ref> It is also used in [[infrared detector]]s. Thallium is highly [[toxic]] and was used in [[rat poison]]s and [[insecticide]]s. Its use has been reduced or eliminated in many countries because of its nonselective toxicity. Because of its use for [[murder]], thallium has gained the nicknames "The Poisoner's Poison" and "Inheritance Powder" (alongside [[arsenic]]).<ref>{{cite book|title = The Boron Elements: Boron, Aluminum, Gallium, Indium, Thallium| page = 14|first =Heather|last = Hasan|year = 2009| isbn = 978-1-4358-5333-1|publisher = Rosen Publishing Group}}</ref>

===Lead===
{{main|Lead}}
'''Lead''' is a main-group [[Chemical element|element]] in the [[carbon group]] with the symbol '''Pb''' (from {{langx|la|plumbum}}) and [[atomic number]] 82. Lead is a soft, [[malleable]] [[other metal]]. It is also counted as one of the [[heavy metal (chemistry)|heavy metal]]s. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed to air. Lead has a shiny chrome-silver luster when it is melted into a liquid.

Lead is used in building construction, [[lead–acid battery|lead-acid batteries]], [[bullet]]s and [[lead shot|shot]]s, weights, as part of [[solder]]s, [[pewter]]s, [[fusible alloy]]s and as a [[radiation shield]]. Lead has the highest [[atomic number]] of all of the [[stable element]]s, although the next higher element, [[bismuth]], has a [[half-life]] that is so long (much longer than the age of the universe) that it can be considered stable. Its four stable isotopes have 82 [[proton]]s, a [[magic number (physics)|magic number]] in the [[nuclear shell model]] of [[atomic nuclei]].

Lead, at certain exposure levels, is a poisonous substance to animals as well as for human beings. It damages the [[nervous system]] and causes [[brain]] disorders. Excessive lead also causes blood disorders in mammals. Like the element [[mercury (element)|mercury]], another heavy metal, lead is a [[neurotoxin]] that accumulates both in soft tissues and the bones. [[Lead poisoning]] has been documented from [[ancient Rome]], [[ancient Greece]], and [[History of China#Ancient China|ancient China]].

===Bismuth===
{{main|Bismuth}}
'''Bismuth''' is a [[chemical element]] with symbol '''Bi''' and [[atomic number]] 83. Bismuth, a trivalent [[other metal]], chemically resembles [[arsenic]] and [[antimony]]. Elemental bismuth may occur naturally uncombined, although its sulfide and oxide form important commercial ores. The [[free element]] is 86% as dense as [[lead]]. It is a brittle metal with a silvery white color when newly made, but often seen in air with a pink tinge owing to the surface oxide. Bismuth metal has been known from ancient times, although until the 18th century it was often confused with lead and tin, which each have some of bismuth's bulk physical properties. The etymology is uncertain but possibly comes from Arabic {{Transliteration|ar|bi ismid}} meaning having the properties of antimony<ref>[http://webmineral.com/data/Bismuth.shtml Bismuth]. Web Mineral. Retrieved on 2011-12-17.</ref> or German words {{lang|de|weisse masse}} or {{lang|de|wismuth}}  meaning "white mass".<ref name="arizona1">{{cite book|editor1=Anthony, John W. |editor2=Bideaux, Richard A. |editor3=Bladh, Kenneth W. |editor4=Nichols, Monte C. |title=Handbook of Mineralogy|publisher=Mineralogical Society of America |place=Chantilly, VA, US |volume=I (Elements, Sulfides, Sulfosalts) |chapter-url=http://rruff.geo.arizona.edu/doclib/hom/bismuth.pdf|chapter=Bismuth |date=1990 |access-date=December 5, 2011 |isbn=978-0-9622097-0-3 }}</ref>

Bismuth is the most naturally [[Diamagnetism|diamagnetic]] of all metals, and only [[mercury (element)|mercury]] has a lower [[thermal conductivity]].

Bismuth has classically been considered to be the heaviest naturally occurring stable element, in terms of atomic mass. Recently, however, it has been found to be very slightly radioactive: its only primordial isotope [[bismuth-209]] decays via [[alpha decay]] into [[thallium-205]] with a [[half-life]] of more than a [[1000000000 (number)|billion]] times the estimated [[age of the universe]].<ref>{{cite news| url=http://physicsweb.org/articles/news/7/4/16| title=Bismuth breaks half-life record for alpha decay| date=2003-04-23| publisher=Physicsweb| first=Belle| last= Dumé}}</ref>

Bismuth compounds (accounting for about half the production of bismuth) are used in [[cosmetics]], pigments, and a few pharmaceuticals. Bismuth has unusually low [[toxicity]] for a heavy metal. As the toxicity of [[lead]] has become more apparent in recent years, alloy uses for bismuth metal (presently about a third of bismuth production), as a replacement for lead, have become an increasing part of bismuth's commercial importance.

===Polonium===
{{main|Polonium}}
'''Polonium''' is a [[chemical element]] with the symbol '''Po''' and [[atomic number]] 84, discovered in 1898 by [[Marie Curie|Marie Skłodowska-Curie]] and [[Pierre Curie]]. A rare and highly [[radioactive]] element, polonium is chemically similar to [[bismuth]]<ref>{{cite web| url = http://hyperphysics.phy-astr.gsu.edu/hbase/pertab/Po.html |title = Polonium| access-date = 2009-05-05}}</ref> and [[tellurium]], and it occurs in [[uranium]] [[ore]]s. Polonium has been studied for possible use in heating [[spacecraft]]. As it is unstable, all [[isotopes of polonium]] are radioactive. There is disagreement as to whether polonium is a [[post-transition metal]] or [[metalloid]].<ref>{{cite journal| doi=10.1021/ed100308w |title = Polonium and Astatine Are Not Semimetals|journal= Journal of Chemical Education| year=2010| last1=Hawkes| first1=Stephen J.| volume=87| issue=8| pages=783 |bibcode = 2010JChEd..87..783H }}</ref><ref>{{cite web |url=http://periodic.lanl.gov/metal.shtml |title=Characterizing the Elements |author=<!--Staff writer(s); no by-line.--> |publisher=[[Los Alamos National Laboratory]] |access-date=4 March 2013}}</ref>

===Astatine===
{{main|Astatine}}
'''Astatine''' is a [[radioactive]] [[chemical element]] with the symbol '''At''' and [[atomic number]] 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the [[periodic table]]. Earlier studies have shown this element follows periodic trends, being the heaviest known [[halogen]], with [[melting point|melting]] and [[boiling point]]s being higher than those of lighter halogens.

Until recently most of the chemical characteristics of astatine were inferred from comparison with other elements; however, important studies have already been done. The main difference between astatine and [[iodine]] is that the HAt molecule is chemically a [[hydride]] rather than a [[halide]]; however, in a fashion similar to the lighter halogens, it is known to form ionic astatides with metals. Bonds to [[Nonmetal (chemistry)|nonmetal]]s result in positive [[oxidation state]]s, with +1 best portrayed by monohalides and their derivatives, while the higher are characterized by bond to oxygen and carbon. Attempts to synthesize astatine fluoride have been met with failure. The second longest-living astatine-211 is the only one to find a commercial use, being useful as an [[alpha decay|alpha emitter]] in medicine; however, only extremely small quantities are used, and in larger ones it is very hazardous, as it is intensely radioactive.

Astatine was first produced by [[Dale R. Corson]], [[Kenneth Ross MacKenzie]], and [[Emilio Segrè]] in the [[University of California, Berkeley]] in 1940. Three years later, it was found in nature; however, with an estimated amount of less than 28&nbsp;grams (1&nbsp;oz) at given time, astatine is the least abundant element in Earth's crust among non-[[transuranium element]]s. Among astatine isotopes, four (with [[mass number]]s 215, 217, 218 and 219) are present in nature as the result of decay of heavier elements; however, the most stable astatine-210 and the industrially used astatine-211 are not.

===Radon===
{{main|Radon}}
'''Radon''' is a [[chemical element]] with symbol '''Rn''' and [[atomic number]] 86. It is a [[radioactive decay|radioactive]], colorless, odorless, tasteless<ref>{{Cite book|title=Britannica Concise Encyclopedia|publisher=Encyclopaedia Britannica: Britannica Digital Learning|year=2017|via=Credo Reference}}</ref> [[noble gas]], occurring naturally as the decay product of [[uranium]] or [[thorium]]. Its most stable [[isotope]], [[Radon-222|<sup>222</sup>Rn]], has a [[half-life]] of 3.8 days. Radon is one of the densest substances that remains a [[gas]] under normal conditions. It is also the only gas that is radioactive under normal conditions, and is considered a health hazard due to its radioactivity. Intense radioactivity also hindered chemical studies of radon and only a few compounds are known.

Radon is formed as part of the normal radioactive [[decay chain]] of uranium and thorium. Uranium and thorium have been around since the earth was formed and their [[isotopes of thorium|most common isotope]] has a very long half-life (14.05 billion years). Uranium and thorium, [[radium]], and thus radon, will continue to occur for millions of years at about the same concentrations as they do now.<ref name=USPHS90>[http://www.bvsde.paho.org/bvstox/i/fulltext/toxprofiles/radon.pdf Toxological profile for radon] {{Webarchive|url=https://web.archive.org/web/20160415161629/http://www.bvsde.paho.org/bvstox/i/fulltext/toxprofiles/radon.pdf |date=2016-04-15 }}, [[Agency for Toxic Substances and Disease Registry]], U.S. Public Health Service, In collaboration with U.S. Environmental Protection Agency, December 1990.</ref> As the radioactive gas of radon decays, it produces new radioactive elements called radon daughters or decay products. Radon daughters are solids and stick to surfaces such as dust particles in the air. If contaminated dust is inhaled, these particles can stick to the airways of the lung and increase the risk of developing lung cancer.<ref>{{cite web|url=http://www.mass.gov/eohhs/consumer/community-health/environmental-health/exposure-topics/radiation/radon/public-health-fact-sheet-on-radon.html |title=Public Health Fact Sheet on Radon – Health and Human Services |publisher=Mass.Gov |access-date=2011-12-04}}</ref>

Radon is responsible for the majority of the public exposure to [[ionizing radiation]]. It is often the single largest contributor to an individual's [[background radiation]] dose, and is the most variable from location to location. Radon gas from natural sources can accumulate in buildings, especially in confined areas such as attics and basements. It can also be found in some [[Spring (hydrosphere)|spring waters]] and hot springs.<ref>{{cite web|title=Facts about Radon|publisher=Facts about|url=http://www.facts-about.org.uk/science-element-radon.htm|access-date=2008-09-07|url-status=dead|archive-url=https://web.archive.org/web/20050222004131/http://www.facts-about.org.uk/science-element-radon.htm|archive-date=2005-02-22}}</ref>

[[Epidemiological]] studies have shown a clear link between breathing high concentrations of radon and incidence of [[lung cancer]]. Thus, radon is considered a significant contaminant that affects [[indoor air quality]] worldwide. According to the [[United States Environmental Protection Agency]], radon is the second most frequent cause of lung cancer, after cigarette smoking, causing 21,000 lung cancer deaths per year in the [[United States]]. About 2,900 of these deaths occur among people who have never smoked. While radon is the second most frequent cause of lung cancer, it is the number one cause among non-smokers, according to EPA estimates.<ref name="epa">{{cite web|url=http://www.epa.gov/radon/pubs/citguide.html|title=A Citizen's Guide to Radon|date=October 12, 2010|work=www.epa.gov|publisher=[[United States Environmental Protection Agency]]|access-date=January 29, 2012}}</ref>