Final answer:
The compound formed between calcium and fluorine is CaF₂, also known as calcium fluoride, with a 1:2 ratio of calcium to fluorine corresponding to their charges of +2 and -1, respectively. The FCC structure of the crystal lattice confirms this stoichiometry.
Step-by-step explanation:
The correct formula for the compound formed between calcium and fluorine is CaF₂. Calcium ions have a charge of +2, and fluoride ions have a charge of -1. To neutralize these charges and form a stable ionic compound, two fluoride ions are needed for every calcium ion. This is confirmed by examining the crystal lattice structure of calcium fluoride. In a face-centered cubic (FCC) unit cell for calcium fluoride, calcium ions are at the lattice points, and fluoride ions occupy the tetrahedral sites, resulting in a 1:2 ratio of calcium to fluorine.
The mineral fluorite is composed of calcium fluoride (CaF₂) and forms when calcium and fluoride ions precipitate from groundwater. This compound demonstrates a simple cubic array structure with calcium ions in half of the cubic holes and fluoride ions occupying the tetrahedral sites within the structure.
Calcium fluoride can also be synthesized through a reaction of aqueous calcium chloride and sodium fluoride, producing CaF₂ and aqueous sodium chloride. The ratio of calcium to fluorine in a unit cell of CaF₂ is integral to its structure and stoichiometry, cementing CaF₂ as the correct compound.