Editing Sodium chloride (section)

==Chemistry==

[[File:Natrium chloride kristal under microscope.jpg|thumb|Sodium chloride crystal under microscope.]]
[[File:NaCl octahedra.svg|thumb|NaCl octahedra. The yellow stipples represent the electrostatic force between the ions of opposite charge]]
===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>

{{Clear}}

===Aqueous solutions===
[[File:WatNaCl.png|thumb|right|upright=1.15|Phase diagram of water–NaCl mixture]]
The attraction between the Na<sup>+</sup> and Cl<sup>−</sup> ions in the solid is so strong that only highly [[polar solvent]]s like water dissolve NaCl well.

When dissolved in water, the sodium chloride framework disintegrates as the Na<sup>+</sup> and Cl<sup>−</sup> ions become surrounded by polar water molecules. These solutions consist of [[metal aquo complex]] with the formula [Na(H<sub>2</sub>O)<sub>8</sub>]<sup>+</sup>, with the Na–O distance of 250&nbsp;[[picometer|pm]]. The chloride ions are also strongly solvated, each being surrounded by an average of six molecules of water.<ref name="Lincoln">Lincoln, S. F.; Richens, D. T. and Sykes, A. G. (2003) "Metal Aqua Ions" Comprehensive Coordination Chemistry II Volume 1, pp. 515–555. {{doi|10.1016/B0-08-043748-6/01055-0}}.</ref> Solutions of sodium chloride have very different properties from pure water. The [[eutectic point]] is {{convert|−21.12|C|F}} for 23.31% [[mass fraction (chemistry)#Mass percentage|mass fraction]] of salt, and the boiling point of saturated salt solution is near {{convert|108.7|C|F}}.<ref name="u1">Elvers, B. ''et al.'' (ed.) (1991) ''Ullmann's Encyclopedia of Industrial Chemistry'', 5th ed. Vol. A24, Wiley, p. 319, {{ISBN|978-3-527-20124-2}}.</ref>

===pH of sodium chloride solutions===
The [[pH]] of a sodium chloride solution remains ≈7 due to the extremely weak basicity of the Cl<sup>−</sup> ion, which is the conjugate base of the [[Hydrochloric acid|strong acid HCl]]. In other words, NaCl has no effect on system pH<ref>{{cite web |url=https://www.flinnsci.com/api/library/Download/1f87f104ec4b4492a621f480797fbab1 |title=Acidic, Basic, and Neutral Salts |date=2016 |website=Flinn Scientific Chem Fax |access-date=18 September 2018 |quote=Neutralization of a strong acid and a strong base gives a neutral salt. |archive-date=19 September 2018 |archive-url=https://web.archive.org/web/20180919024828/https://www.flinnsci.com/api/library/Download/1f87f104ec4b4492a621f480797fbab1 |url-status=live }}</ref> in diluted solutions where the effects of ionic strength and activity coefficients are negligible.
{| class="wikitable" style="float:right; margin-left:1em;"
! {{Chemical datatable header}}|Solubility of NaCl<br>(g NaCl / 1&nbsp;kg of solvent at {{convert|25|C|F}})<ref>{{cite book |last=Burgess |first=J |title=Metal Ions in Solution |publisher=Ellis Horwood |year=1978 |isbn=978-0-85312-027-8 |location=New York}}</ref>
|-
| [[Water (molecule)|Water]] || 360
|-
| [[Formamide]] || 94
|-
| [[Glycerin]] || 83
|-
| [[Propylene glycol]] || 71
|-
| [[Formic acid]] || 52
|-
| Liquid [[ammonia]] || 30.2
|-
| [[Methanol]] || 14
|-
| [[Ethanol]] || 0.65
|-
| [[Dimethylformamide]] || 0.4
|-
| [[Propan-1-ol]] || 0.124
|-
| [[Sulfolane]] || 0.05
|-
| [[Butan-1-ol]] || 0.05
|-
| [[Propan-2-ol]] || 0.03
|-
| [[Pentan-1-ol]] || 0.018
|-
| [[Acetonitrile]] || 0.003
|-
| [[Acetone]] || 0.00042
|}

===Stoichiometric and structure variants===
Common salt has a 1:1 molar ratio of sodium and chlorine. In 2013, compounds of sodium and chloride of different [[stoichiometry|stoichiometries]] have been discovered; five new compounds were predicted (e.g., [[Na3Cl|Na<sub>3</sub>Cl]], [[Na2Cl|Na<sub>2</sub>Cl]], [[Na3Cl2|Na<sub>3</sub>Cl<sub>2</sub>]], [[NaCl3|NaCl<sub>3</sub>]], and [[NaCl7|NaCl<sub>7</sub>]]). The existence of some of them has been experimentally confirmed at high pressures and other conditions: cubic and orthorhombic NaCl<sub>3</sub>, two-dimensional metallic tetragonal Na<sub>3</sub>Cl and exotic hexagonal NaCl.<ref>{{cite journal |last1=Tikhomirova |first1=K. A. |last2=Tantardini |first2=C. |last3=Sukhanova |first3=E. V. |last4=Popov |first4=Z. I. |last5=Evlashin |first5=S. A. |last6=Tarkhov |first6=M. A. |last7=Zhdanov |first7=V. L. |year=2020 |title=Exotic Two-Dimensional Structure: The first case of Hexagonal NaCl |journal=The Journal of Physical Chemistry Letters |volume=11 |issue=10 |pages=3821–3827 |doi=10.1021/acs.jpclett.0c00874 |pmid=32330050 |s2cid=216130640 }}</ref> This indicates that compounds violating chemical intuition are possible, in simple systems under non-ambient conditions.<ref>{{cite journal |last1=Zhang |first1=W. |last2=Oganov |first2=A. R. |last3=Goncharov |first3=A. F. |last4=Zhu |first4=Q. |last5=Boulfelfel |first5=S. E. |last6=Lyakhov |first6=A. O. |last7=Stavrou |first7=E. |last8=Somayazulu |first8=M. |last9=Prakapenka |first9=V. B. |last10=Konôpková |first10=Z. |year=2013 |title=Unexpected Stable Stoichiometries of Sodium Chlorides |journal=Science |volume=342 |issue=6165 |pages=1502–1505 |arxiv=1310.7674 |bibcode=2013Sci...342.1502Z |doi=10.1126/science.1244989 |pmid=24357316 |s2cid=15298372 }}</ref>