Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white solid that is practically insoluble in water. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.
3D model (JSmol)
CompTox Dashboard (EPA)
|Molar mass||78.075 g·mol−1|
|Appearance||White crystalline solid (single crystals are transparent)|
|Melting point||1,418 °C (2,584 °F; 1,691 K)|
|Boiling point||2,533 °C (4,591 °F; 2,806 K)|
|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
Refractive index (nD)
|cubic crystal system, cF12|
a = 5.451 Å, b = 5.451 Å, c = 5.451 Å
α = 90°, β = 90°, γ = 90°
|Ca, 8, cubic|
F, 4, tetrahedral
|Occupational safety and health (OHS/OSH):|
|Reacts with concentrated sulfuric acid to produce hydrofluoric acid|
|NFPA 704 (fire diamond)|
|Lethal dose or concentration (LD, LC):|
LDLo (lowest published)
|>5000 mg/kg (oral, guinea pig)|
4250 mg/kg (oral, rat)
|Safety data sheet (SDS)||ICSC 1323|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Chemical structure Edit
The compound crystallizes in a cubic motif called the fluorite structure.
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. 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 Edit
The gas phase is noteworthy for failing the predictions of VSEPR theory; the CaF2 molecule is not linear like MgF2, but bent with a bond angle of approximately 145°; the strontium and barium dihalides also have a bent geometry. It has been proposed that this is due to the fluoride ligands interacting with the electron core or the d-subshell of the calcium atom.
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:
- CaCO3 + 2 HF → CaF2 + CO2 + H2O
Naturally occurring CaF2 is the principal source of hydrogen fluoride,[clarification needed] 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. Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:
- CaF2 + H2SO4 → CaSO4(solid) + 2 HF
Calcium fluoride is used to manufacture optical components such as windows and lenses, used in thermal imaging systems, spectroscopy, telescopes, and excimer lasers (used for photolithography in the form of a fused lens). 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. It also allows much smaller wavelengths to pass through.
CaF2 is classified as "not dangerous", although reacting it with sulfuric acid produces hydrofluoric acid, which is highly corrosive and toxic. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air.
See also Edit
- 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.
- 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.
- 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)