Editing Sodium chloride (section)

===Solid sodium chloride===
{{See also|Cubic crystal system}}
In solid sodium chloride, each ion is surrounded by six ions of the opposite charge as expected on electrostatic grounds. The surrounding ions are located at the vertices of a regular [[octahedron]]. In the language of [[close-packing]], the larger [[chloride]] [[ion]]s (167 pm in size<ref name="Shannon">{{cite journal |doi=10.1107/S0567739476001551 |title=Revised effective ionic radii and systematic studies of interatomic distances in halides and chalcogenides |author=R. D. Shannon |journal=Acta Crystallogr A |volume=32 |issue=5 |year=1976 |pages=751–767 |bibcode=1976AcCrA..32..751S |doi-access=}}</ref>) are arranged in a cubic array whereas the smaller [[sodium]] ions (116 pm<ref name=Shannon/>) fill all the cubic gaps (octahedral voids) between them. This same basic structure is found in many other [[chemical compound|compounds]] and is commonly known as the [[NaCl structure]] or rock salt crystal structure. It can be represented as a [[cubic crystal system|face-centered cubic]] (fcc) lattice with a two-atom basis or as two interpenetrating face centered cubic lattices. The first atom is located at each lattice point, and the second atom is located halfway between lattice points along the fcc unit cell edge.

Solid sodium chloride has a melting point of 801&nbsp;°C and liquid sodium chloride boils at 1465&nbsp;°C. Atomic-resolution real-time video imaging allows visualization of the initial stage of crystal nucleation of sodium chloride.<ref>{{cite journal |last1=Nakamuro |first1=Takayuki |last2=Sakakibara |first2=Masaya |last3=Nada |first3=Hiroki |last4=Harano |first4=Koji |last5=Nakamura |first5=Eiichi |year=2021 |title=Capturing the Moment of Emergence of Crystal Nucleus from Disorder |journal=Journal of the American Chemical Society |volume=143 |issue=4 |pages=1763–1767 |doi=10.1021/jacs.0c12100 |pmid=33475359 |doi-access=free|bibcode=2021JAChS.143.1763N }}</ref>

The [[Thermal conductivity]] of sodium chloride as a function of temperature has a maximum of 2.03&nbsp;W/(cm&nbsp;K) at {{convert|8|K}} and decreases to 0.069 at {{convert|314|K}}. It also decreases with [[doping (semiconductor)|doping]].<ref>{{cite book |last1=Sirdeshmukh |first1=Dinker B. |url=https://books.google.com/books?id=X-yL7EgMK6wC&pg=PA68 |title=Alkali halides: a handbook of physical properties |last2=Sirdeshmukh, Lalitha |last3=Subhadra, K. G. |publisher=Springer |year=2001 |isbn=978-3-540-42180-1 |pages=65, 68 |name-list-style=amp}}</ref>

[[File:NaCl(H2O)2slab.png|thumb|left|upright=1.25|View of one slab of [[hydrohalite]], NaCl·2H<sub>2</sub>O. (red = O, white = H, green = Cl, purple = Na).<ref>{{cite journal |last1=Klewe |first1=B |last2=Pedersen |year=1974 |title=The crystal structure of sodium chloride dihydrate |journal=Acta Crystallogr. |volume=B30 |issue=10 |pages=2363–2371 |doi=10.1107/S0567740874007138 |doi-access=|bibcode=1974AcCrB..30.2363K }}</ref>]]
From cold (sub-freezing) solutions, salt crystallises with [[water of hydration]] as [[hydrohalite]] (the dihydrate NaCl·2{{Chem2|H2O}}).<ref>Water-NaCl phase diagram. Lide, CRC Handbook of Chemistry and Physics, 86 ed (2005-2006), CRC pages 8-71, 8-116</ref>

In 2023, it was discovered that under pressure, sodium chloride can form the hydrates NaCl·8.5H<sub>2</sub>O and NaCl·13H<sub>2</sub>O.<ref>{{cite news |last1=University of Washington |title=Newly discovered form of salty ice could exist on surface of extraterrestrial moons |url=https://phys.org/news/2023-02-newly-salty-ice-surface-extraterrestrial.html |agency=Phys.org |access-date=21 February 2023 |archive-date=21 February 2023 |archive-url=https://web.archive.org/web/20230221035605/https://phys.org/news/2023-02-newly-salty-ice-surface-extraterrestrial.html |url-status=live }}</ref>

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