CaCl2
calcium chloride · calcium dichloride
Calcium chloride (CaCl2) is a stable ionic salt of calcium and chlorine. At room temperature, anhydrous CaCl2 has an orthorhombic distorted rutile-type crystal structure that changes into a tetragonal rutile structure at higher temperatures. Electronically, it is a wide-band-gap insulator.
About calcium chloride
What is CaCl2 and what structure does it adopt?
CaCl2 is a binary alkaline-earth halide salt made of calcium cations and chloride anions. At ambient temperature and pressure, anhydrous CaCl2 crystallizes in an orthorhombic distorted rutile structure in space group Pnnm. Each calcium cation is octahedrally coordinated by six chloride anions. On heating, it goes through a continuous ferroelastic phase transition to the tetragonal rutile structure in space group P4_2/mnm. Calcium chloride also forms a series of hydrates, CaCl2·nH2O with n = 1, 2, 4 and 6, and has high-pressure polymorphs.
What is calcium chloride used for?
Calcium chloride is an industrial and laboratory chemical valued because it is strongly hygroscopic and deliquescent and lowers the freezing point of water. Its main uses are melting ice and preventing ice formation on roads and walkways, and suppressing dust on unpaved surfaces. Anhydrous calcium chloride is widely used as a desiccant, for example in laboratory drying tubes. Other uses include refrigeration brines, accelerating the setting of concrete, drilling fluids, and food processing additives.
How stable and synthesizable is CaCl2?
CaCl2 is a thermodynamically stable compound. It is easily made by reacting calcium hydroxide, calcium oxide or calcium carbonate with hydrochloric acid. It is also recovered as a byproduct of industrial processes such as the Solvay process. It does not decompose on ordinary heating, but the anhydrous form must be kept sealed because it quickly absorbs moisture from the air.
Is CaCl2 an insulator or a conductor?
Solid CaCl2 is an electrical insulator with a wide band gap. Its electrons are tightly bound in the ionic lattice, so the pure solid has essentially no free charge carriers. When it is dissolved in water or melted, the ions become mobile, and the solution or melt conducts electricity as an electrolyte.
How does CaCl2 compare to other alkaline-earth halides?
Among the Group 2 halides, the calcium cation is intermediate in size: larger than magnesium but smaller than strontium and barium. Calcium fluoride (CaF2) has the fluorite structure and is poorly soluble in water. Calcium chloride, by contrast, has a distorted rutile structure under ambient conditions and is very soluble in water and deliquescent.
Key Properties
Cross-validated computational properties for calcium chloride, aggregated across 5 databases.
Band GapEnergy needed to move an electron from the valence band to the conduction band. Lower or zero values tend to behave more metallic; larger gaps are more insulating or semiconducting.
Energy Above HullThermodynamic distance from the most stable set of competing phases. 0 eV/atom is on the convex hull; small positive values may still be experimentally accessible.
StabilityA plain-language summary of the best reported energy-above-hull result. It reflects whether the lowest-energy structure is on, near, or far from the stability hull.
StructuresCount of reported calculated crystal structures for this formula, including alternate polymorphs, source databases, and observed space groups.
Cross-Source DFT Agreement
How well independent DFT databases agree on the thermodynamics of CaCl2. Tight agreement means computed properties can be trusted without re-running calculations.
Agreement ScoreA normalized confidence score summarizing how closely independent DFT databases agree. Higher scores mean tighter cross-source agreement.
Hull SpreadDifference between the highest and lowest energy-above-hull values reported by comparable sources. Smaller spread means less thermodynamic disagreement.
Sources ComparedNumber and names of computational sources with comparable entries for this formula.
Space Group ConsensusWhether independent sources predict the same crystal symmetry for the lowest-energy structure.
Reported Structures
Lowest-energy structures reported for CaCl2, ranked by energy above hull.
| Space GroupSymmetry classification of the crystal arrangement. The number is the international space-group index. | Crystal SystemBroad lattice family, such as cubic, tetragonal, monoclinic, or triclinic, derived from unit-cell symmetry. | Band Gap (eV)Electronic gap calculated for this specific reported structure, measured in electronvolts. | E above hull (eV/atom)Thermodynamic distance from the convex hull for this structure, normalized per atom. Lower is generally more stable. | E/atom (eV)Computed total energy normalized per atom. Use energy above hull, not this value alone, when comparing stability. | Density (g/cm³)Mass per relaxed crystal volume, reported in grams per cubic centimeter. |
|---|---|---|---|---|---|
| Pbcn (No. 60) | orthorhombic | 5.60 | 0.0000 | -4.706 | 2.20 |
| Pbcn (No. 60) | orthorhombic | 5.54 | 0.0000 | -2.530 | — |
| — | — | 5.48 | 0.0000 | -2.653 | — |
| — | — | 5.48 | 0.0004 | -2.652 | — |
| Pnnm (No. 58) | orthorhombic | 5.40 | 0.0011 | -4.705 | 2.16 |
| — | — | 5.67 | 0.0013 | -2.651 | — |
| — | — | 5.43 | 0.0016 | -2.651 | — |
| P42/mnm (No. 136) | tetragonal | 5.35 | 0.0019 | -4.704 | 2.15 |
| Pnnm (No. 58) | orthorhombic | 5.42 | 0.0021 | -2.528 | — |
| Pnnm (No. 58) | orthorhombic | 5.42 | 0.0021 | -2.528 | — |
| P42/mnm (No. 136) | tetragonal | 5.29 | 0.0061 | -2.524 | — |
| P42/mnm (No. 136) | tetragonal | 5.29 | 0.0061 | -2.524 | — |
Synthesis Routes
Literature-extracted synthesis procedures targeting CaCl2.
Applications
Where calcium chloride is used.
Frequently Asked Questions
Common questions about calcium chloride, answered from cross-validated data and the published literature.
Is CaCl2 soluble in water?
Yes. Calcium chloride is highly soluble in water and deliquescent. Dissolving the anhydrous salt releases a lot of heat.
Does CaCl2 conduct electricity?
What is the crystal structure of CaCl2?
Is calcium chloride safe to handle?
Why does CaCl2 melt ice effectively?
What is CaCl2?
What is CaCl2 used for?
What is the band gap of CaCl2?
Is CaCl2 a metal, semiconductor, or insulator?
Is CaCl2 thermodynamically stable?
What is the density of CaCl2?
How many polymorphs of CaCl2 are known?
How is CaCl2 synthesized?
What elements does CaCl2 contain?
Where does the data for CaCl2 come from?
Data sources & attribution
- materials_project — Data from the Materials Project (materialsproject.org). Cite: Jain et al., APL Materials 1, 011002 (2013). (CC-BY-4.0)
- jarvis — Data from JARVIS (jarvis.nist.gov), NIST. Cite: Choudhary et al., npj Comp. Mater. 6, 173 (2020). (LicenseRef-US-Gov-PD)
- oqmd — Data from the OQMD (oqmd.org). Cite: Saal et al., JOM 65, 1501 (2013); Kirklin et al., npj Comp. Mater. 1, 15010 (2015). (CC-BY-4.0)
Analyze CaCl2 in the Lattice Graph platform
Polymorph comparison, confidence scoring, supply-chain risk, and patent monitoring — across 85 source databases.
Explore the Platform →