Here's why:
* Valence Electrons: Alkaline earth metals have two valence electrons.
* Ionic Bonding: They tend to lose these two electrons to form +2 cations.
* Chlorine: Chlorine, a halogen, gains one electron to form a -1 anion (Cl⁻).
* Balancing Charges: To achieve a neutral compound, two chlorine ions (2 x Cl⁻ = -2 charge) are needed to balance the +2 charge of the alkaline earth metal cation.
Examples:
* Calcium chloride (CaCl₂): Ca²⁺ + 2Cl⁻ → CaCl₂
* Magnesium chloride (MgCl₂): Mg²⁺ + 2Cl⁻ → MgCl₂
Important Note: While most alkaline earth metals form chlorides with the Cl₂ formula, some exceptions exist. For example, beryllium chloride (BeCl₂) is a covalent compound and its formula is BeCl₂.
