Calcium fluoride

Identifiers

CAS Number

7789-75-5^Y

3D model (JSmol)

Interactive image
Interactive image

ChEBI

CHEBI:35437^Y

ChemSpider

23019^Y

ECHA InfoCard

100.029.262

EC Number

232-188-7

PubChem CID

24617

RTECS number

EW1760000

UNII

O3B55K4YKI^Y

CompTox Dashboard (EPA)

DTXSID4050487

InChI

InChI=1S/Ca.2FH/h;2*1H/q+2;;/p-2^Y
Key: WUKWITHWXAAZEY-UHFFFAOYSA-L^Y
InChI=1/Ca.2FH/h;2*1H/q+2;;/p-2
Key: WUKWITHWXAAZEY-NUQVWONBAZ

SMILES

[Ca+2].[F-].[F-]
F[Ca]F

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 (K_sp)

3.9 × 10⁻¹¹ ^[1]

Solubility

insoluble in acetone
slightly soluble in acid

Magnetic susceptibility (χ)

-28.0·10⁻⁶ cm³/mol

Refractive index (n_D)

1.4338

Structure

Crystal structure

cubic crystal system, cF12^[2]

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

Occupational safety and health (OHS/OSH):

Main hazards

Reacts with concentrated sulfuric acid to produce hydrofluoric acid

NFPA 704 (fire diamond)

Flash point

Non-flammable

Lethal dose or concentration (LD, LC):

LD_Lo (lowest published)

>5000 mg/kg (oral, guinea pig)
4250 mg/kg (oral, rat)^[3]

Safety data sheet (SDS)

ICSC 1323

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).

Y verify (what is ^YN ?)

Infobox references

Chemical compound

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.

Chemical structure

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.^[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 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.^[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

Others

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.^{[citation needed]} It also allows much smaller wavelengths to pass through.^{[citation needed]}

Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. It forms when fluorine combines with calcium.^{[citation needed]}

Safety

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.^[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.
^ ^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. ISBN 978-3527306732.
^ 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.