Editing Tetrahedron (section)

===Chemistry===
<div>[[Image:Ammonium-3D-balls.png|100px|thumb|The [[ammonium]] ion is tetrahedral]]</div>
[[Image:Tetrahedral_angle_calculation.svg|thumb|216px|<!-- specify width as minus sign vanishes at most sizes --> Calculation of the central angle with a [[dot product]] ]]
{{main|Tetrahedral molecular geometry}}
The tetrahedron shape is seen in nature in [[covalent bond|covalently bonded]] molecules. All [[Orbital hybridisation|sp<sup>3</sup>-hybridized]] atoms are surrounded by atoms (or [[lone pair|lone electron pairs]]) at the four corners of a tetrahedron. For instance in a [[methane]] molecule ({{chem|CH|4}}) or an [[ammonium]] ion ({{chem|NH|4|+}}), four hydrogen atoms surround a central carbon or nitrogen atom with tetrahedral symmetry. For this reason, one of the leading journals in organic chemistry is called ''[[Tetrahedron (journal)|Tetrahedron]]''. The [[central angle]] between any two vertices of a perfect tetrahedron is arccos(−{{sfrac|1|3}}), or approximately 109.47°.<ref name="pubs.acs.org">{{cite journal|doi=10.1021/ed022p145 | volume=22 | issue=3 | title=Valence angle of the tetrahedral carbon atom | year=1945 | journal=Journal of Chemical Education | page=145 | last1 = Brittin | first1 = W. E.| bibcode=1945JChEd..22..145B }}</ref>

[[Water]], {{chem|H|2|O}}, also has a tetrahedral structure, with two hydrogen atoms and two lone pairs of electrons around the central oxygen atoms. Its tetrahedral symmetry is not perfect, however, because the lone pairs repel more than the single O–H bonds.

Quaternary [[phase diagram]]s of mixtures of chemical substances are represented graphically as tetrahedra.

However, quaternary phase diagrams in [[communication engineering]] are represented graphically on a two-dimensional plane.

There are molecules with the shape based on four nearby atoms whose bonds form the sides of a tetrahedral structure, such as [[Allotropes of phosphorus|white phosphorus]] allotrope<ref>{{Cite web |title=White phosphorus |url=https://www.acs.org/molecule-of-the-week/archive/w/white-phosphorus.html |access-date=2024-05-26 |website=American Chemical Society |language=en}}</ref> and tetra-''t''-butyltetrahedrane, known derivative of the hypothetical [[tetrahedrane]].