Pengguna:Agung.karjono/Bak pasir/Timbal(II) nitrat: Perbedaan revisi

Belerang adalah [[Mineral (nutrisi)|unsur penting]] untuk semua kehidupan, tetapi hampir selalu dalam bentuk senyawa [[Senyawa organosulfur|organosulfur]] atau sulfida logam. Tiga [[asam amino]] ([[Sisteina|sistein]], {{Ill|sistin|en|cystine}}, dan [[Metionina|metionin]]) dan dua [[vitamin]] ([[biotin]] dan [[Tiamina|tiamin]]) adalah senyawa organosulfur. Banyak [[Kofaktor (biokimia)|kofaktor]] juga mengandung belerang, termasuk [[glutation]], {{Ill|thioredoksin|en|thioredoxin}}, dan {{Ill|Protein besi–belerang|en|iron–sulfur proteins}}. [[Disulfida]], ikatan S–S, memberi kekuatan mekanis dan ketaklarutan protein [[keratin]], yang ditemukan di kulit luar, rambut, dan bulu. Belerang adalah salah satu unsur kimia inti yang dibutuhkan untuk fungsi [[biokimia]] dan [[Makronutrien|unsur hara makro]] bagi semua organisme hidup.
 
==CharacteristicsKarakteristik==
[[File:Burning-sulfur.png|thumb|left|WhenKetika burnedterbakar, sulfurbelerang meltsmeleleh tomenjadi acairan blood-redberwarna liquidmerah anddarah emitsdan amemancarkan bluenyala flameapi biru.]]
 
===PhysicalSifat propertiesfisik===
SulfurBelerang formsmembentuk severalbeberapa polyatomicmolekul moleculespoliatomik. Alotropi Theyang best-knownterkenal allotropeadalah is [[{{Ill|oktasulfur|en|octasulfur]]}}, cyclosiklo-S<sub>8</sub>. The{{Ill|Grup [[pointtitik|en|Point group]] of}} cyclosiklo-S<sub>8</sub> isadalah D<sub>4d</sub> anddan itsmomen dipoledipolnya moment isadalah 0 D.<ref>{{cite journal|last1=Rettig|first1=S. J.|last2=Trotter|first2=J.|title=Refinement of the structure of orthorhombic sulfur, α-S8|journal=Acta Crystallographica Section C|date=15 December 1987|volume=43|issue=12|pages=2260–2262|doi=10.1107/S0108270187088152|url=http://journals.iucr.org/c/issues/1987/12/00/a27614/a27614.pdf}}</ref> Octasulfur is a soft, bright-yellow solid that is odorless, but impure samples have an odor similar to that of [[match]]es.<ref>A strong odor called "smell of sulfur" actually is given off by several sulfur compounds, such as [[hydrogen sulfide]] and [[organosulfur]] compounds.</ref> It melts at {{convert|115.21|C}}, boils at {{convert|444.6|C}} and sublimes easily.<ref name=Greenwd/> At {{convert|95.2|C}}, below its melting temperature, cyclo-octasulfur changes from α-octasulfur to the β-[[polymorphism (materials science)|polymorph]].<ref name= "Greenwood">{{Greenwood&Earnshaw2nd|pages= 645–665}}</ref> The structure of the S<sub>8</sub> ring is virtually unchanged by this phase change, which affects the intermolecular interactions. Between its melting and boiling temperatures, octasulfur changes its allotrope again, turning from β-octasulfur to γ-sulfur, again accompanied by a lower density but increased [[viscosity]] due to the formation of [[polymer]]s.<ref name= "Greenwood"/> At higher temperatures, the viscosity decreases as depolymerization occurs. Molten sulfur assumes a dark red color above {{convert|200|C}}. The density of sulfur is about 2&nbsp;g/cm<sup>3</sup>, depending on the allotrope; all of the stable allotropes are excellent electrical insulators.
 
Sulfur forms several polyatomic molecules. The best-known allotrope is [[octasulfur]], cyclo-S<sub>8</sub>. The [[point group]] of cyclo-S<sub>8</sub> is D<sub>4d</sub> and its dipole moment is 0 D. Octasulfur is a soft, bright-yellow solid that is odorless, but impure samples have an odor similar to that of [[match]]es.<ref>A strong odor called "smell of sulfur" actually is given off by several sulfur compounds, such as [[hydrogen sulfide]] and [[organosulfur]] compounds.</ref> It melts at {{convert|115.21|C}}, boils at {{convert|444.6|C}} and sublimes easily.<ref name="Greenwd" /> At {{convert|95.2|C}}, below its melting temperature, cyclo-octasulfur changes from α-octasulfur to the β-[[polymorphism (materials science)|polymorph]].<ref name="Greenwood">{{Greenwood&Earnshaw2nd|pages= 645–665}}</ref> The structure of the S<sub>8</sub> ring is virtually unchanged by this phase change, which affects the intermolecular interactions. Between its melting and boiling temperatures, octasulfur changes its allotrope again, turning from β-octasulfur to γ-sulfur, again accompanied by a lower density but increased [[viscosity]] due to the formation of [[polymer]]s.<ref name="Greenwood" /> At higher temperatures, the viscosity decreases as depolymerization occurs. Molten sulfur assumes a dark red color above {{convert|200|C}}. The density of sulfur is about 2&nbsp;g/cm<sup>3</sup>, depending on the allotrope; all of the stable allotropes are excellent electrical insulators.
 
===Chemical properties===