To determine which formula represents calcium hydride, we must understand the chemical composition and bonding properties of calcium and hydrogen.
1. Identifying the elements and their charges:
- Calcium (Ca) is an alkaline earth metal that typically forms a +2 charge when it becomes an ion (Ca²⁺).
- Hydrogen (H), when forming a hydride (H⁻), has a -1 charge.
2. Balancing the charges:
- To form a stable compound, the total positive charge must balance the total negative charge. Since calcium has a +2 charge, we need two hydrogen ions, each with a -1 charge, to balance it.
3. Reviewing the options:
- (1) CaH: This formula indicates one calcium ion and one hydrogen ion. This does not balance the charges because the calcium ion's +2 charge is not fully neutralized by a single hydrogen ion's -1 charge.
- (2) CaH₂: This formula indicates one calcium ion and two hydrogen ions. This balances the charges perfectly, as the calcium ion's +2 charge is neutralized by the two hydrogen ions, each with a -1 charge.
- (3) CaOH: This formula indicates one calcium ion, one oxygen ion, and one hydrogen ion. This describes a different compound altogether (calcium hydroxide) and does not match the definition of calcium hydride.
- (4) Ca(OH)₂: This formula indicates one calcium ion and two hydroxide (OH) ions. This describes another different compound (calcium hydroxide) and does not match the definition of calcium hydride.
Therefore, the correct formula for calcium hydride is:
(2) CaH₂
