Calcium fluoride

Calcium fluoride
Identifiers
CAS Number	7789-75-5 ;
3D model (JSmol)	Interactive image; Interactive image;
ChEBI	CHEBI:35437 ;
ChemSpider	23019 ;
ECHA InfoCard	100.029.262
EC Number	232-188-7;
PubChem CID	24617;
RTECS number	EW1760000;
UNII	O3B55K4YKI ;
CompTox Dashboard (EPA)	DTXSID4050487 ;
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Properties
Chemical formula	CaF2
Molar mass	78.075 g·mol−1
Appearance	White crystalline solid (single crystals are transparent)
Density	3.18 g/cm3
Melting point	1,418 °C (2,584 °F; 1,691 K)
Boiling point	2,533 °C (4,591 °F; 2,806 K)
Solubility in water	0.015 g/L (18 °C); 0.016 g/L (20 °C)
Solubility product (Ksp)	3.9 × 10−11
Solubility	insoluble in acetone; slightly soluble in acid
Magnetic susceptibility (χ)	-28.0·10−6 cm3/mol
Refractive index (nD)	1.4338
Structure
Crystal structure	cubic crystal system, cF12
Space group	Fm3m, #225
Lattice constant	a = 5.451 Å, b = 5.451 Å, c = 5.451 Å α = 90°, β = 90°, γ = 90°
Coordination geometry	Ca, 8, cubic; F, 4, tetrahedral
Hazards
Main hazards	Reacts with concentrated sulfuric acid to produce hydrofluoric acid
Safety data sheet	ICSC 1323
NFPA 704 (fire diamond)	0 0 0
Flash point	Non-flammable
	Lethal dose or concentration (LD, LC):
LDLo (lowest published)	>5000 mg/kg (oral, guinea pig); 4250 mg/kg (oral, rat)
Related compounds
Other anions	Calcium chloride; Calcium bromide; Calcium iodide
Other cations	Beryllium fluoride; Magnesium fluoride; Strontium fluoride; Barium fluoride
	Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
	(what is ?)
	Infobox references

Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF₂. It is a white insoluble solid. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.

Chemical structure[]

The compound crystallizes in a cubic motif called the fluorite structure.

Unit cell of CaF₂, known as fluorite structure, from two equivalent perspectives. The second origin is often used when visualising point defects entered on the cation.^[4]

Ca²⁺ centres are eight-coordinate, being centered in a cube of eight F⁻ centres. Each F⁻ centre is coordinated to four Ca²⁺ centres in the shape of a tetrahedron.^[5] Although perfectly packed crystalline samples are colorless, the mineral is often deeply colored due to the presence of F-centers. The same crystal structure is found in numerous ionic compounds with formula AB₂, such as CeO₂, cubic ZrO₂, UO₂, ThO₂, and PuO₂. In the corresponding anti-structure, called the antifluorite structure, anions and cations are swapped, such as Be₂C.

Gas phase[]

The gas phase is noteworthy for failing the predictions of VSEPR theory; the CaF
2 molecule is not linear like MgF
2, but bent with a bond angle of approximately 145°; the strontium and barium dihalides also have a bent geometry.^[6] It has been proposed that this is due to the fluoride ligands interacting with the electron core^[7]^[8] or the d-subshell^[9] of the calcium atom.

Preparation[]

The mineral fluorite is abundant, widespread, and mainly of interest as a precursor to HF. Thus, little motivation exists for the industrial production of CaF₂. High purity CaF₂ is produced by treating calcium carbonate with hydrofluoric acid:^[10]

CaCO₃ + 2 HF → CaF₂ + CO₂ + H₂O

Applications[]

Naturally occurring CaF₂ is the principal source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials. Calcium fluoride in the fluorite state is of significant commercial importance as a fluoride source.^[11] Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:^[12]

CaF₂ + H₂SO₄ → CaSO₄(solid) + 2 HF

Niche uses[]

Calcium fluoride is used to manufacture optical components such as windows and lenses, used in thermal imaging systems, spectroscopy, telescopes, and excimer lasers. It is transparent over a broad range from ultraviolet (UV) to infrared (IR) frequencies. Its low refractive index reduces the need for anti-reflection coatings. Its insolubility in water is convenient as well. Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. It forms when fluorine combines with calcium.

Safety[]

CaF₂ is classified as "not dangerous", although reacting it with sulfuric acid produces very toxic hydrofluoric acid. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m³ in air.^[10]

References[]

^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
^ X-ray Diffraction Investigations of CaF₂ at High Pressure, L. Gerward, J. S. Olsen, S. Steenstrup, M. Malinowski, S. Åsbrink and A. Waskowska, Journal of Applied Crystallography (1992), 25, 578-581 doi:10.1107/S0021889892004096
^ "Fluorides (as F)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
^ Burr, P. A.; Cooper, M. W. D. (2017-09-15). "Importance of elastic finite-size effects: Neutral defects in ionic compounds". Physical Review B. 96 (9): 094107. arXiv:1709.02037. Bibcode:2017PhRvB..96i4107B. doi:10.1103/PhysRevB.96.094107. S2CID 119056949.
^ G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
^ Gillespie, R. J.; Robinson, E. A. (2005). "Models of molecular geometry". Chem. Soc. Rev. 34 (5): 396–407. doi:10.1039/b405359c. PMID 15852152.
^ Bytheway, I.; Gillespie, R. J.; Tang, T. H.; Bader, R.F (1995). "Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba". Inorg. Chem. 34 (9): 2407–2414. doi:10.1021/ic00113a023.
^ Seijo, Luis; Barandiarán, Zoila; Huzinaga, Sigeru (1991). "Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX₂ (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)" (PDF). J. Chem. Phys. 94 (5): 3762. Bibcode:1991JChPh..94.3762S. doi:10.1063/1.459748. hdl:10486/7315.
^ Jump up to: ^a ^b Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307.
^ Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, Renée; Cuer, Jean Pierre (2005), "Fluorine Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, p. 307, doi:10.1002/14356007.a11_307.
^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

External links[]

NIST webbook thermochemistry data
Charles Townes on the history of lasers
National Pollutant Inventory - Fluoride and compounds fact sheet
Crystran Material Data
MSDS (University of Oxford)

[1] Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8

[2] X-ray Diffraction Investigations of CaF₂ at High Pressure, L. Gerward, J. S. Olsen, S. Steenstrup, M. Malinowski, S. Åsbrink and A. Waskowska, Journal of Applied Crystallography (1992), 25, 578-581 doi:10.1107/S0021889892004096

[3] "Fluorides (as F)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).

[4] Burr, P. A.; Cooper, M. W. D. (2017-09-15). "Importance of elastic finite-size effects: Neutral defects in ionic compounds". Physical Review B. 96 (9): 094107. arXiv:1709.02037. Bibcode:2017PhRvB..96i4107B. doi:10.1103/PhysRevB.96.094107. S2CID 119056949.

[5] G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.

[6] Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.

[Gillespie&Robinson-7] Gillespie, R. J.; Robinson, E. A. (2005). "Models of molecular geometry". Chem. Soc. Rev. 34 (5): 396–407. doi:10.1039/b405359c. PMID 15852152.

[Bytheway&Gillespie-8] Bytheway, I.; Gillespie, R. J.; Tang, T. H.; Bader, R.F (1995). "Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba". Inorg. Chem. 34 (9): 2407–2414. doi:10.1021/ic00113a023.

[9] Seijo, Luis; Barandiarán, Zoila; Huzinaga, Sigeru (1991). "Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX₂ (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)" (PDF). J. Chem. Phys. 94 (5): 3762. Bibcode:1991JChPh..94.3762S. doi:10.1063/1.459748. hdl:10486/7315.

[Aigueperse-10] Jump up to: ^a ^b Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307.

[11] Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, Renée; Cuer, Jean Pierre (2005), "Fluorine Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, p. 307, doi:10.1002/14356007.a11_307.

[12] Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

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