Discuss why you figured out the formula of calcium iodide as Cal2 and not Cal.
The correct answer and explanation is :
The chemical formula of calcium iodide is ( \text{CaI}_2 ), not ( \text{CaI} ), and this is based on the way calcium and iodine atoms bond to form a stable ionic compound.
Reasoning Behind the Correct Formula ( \text{CaI}_2 ):
- Calcium’s Ionization:
Calcium (Ca) is an alkaline earth metal in Group 2 of the periodic table. Elements in this group typically have two valence electrons that they readily lose to form cations with a 2+ charge. Therefore, when calcium forms an ion, it becomes ( \text{Ca}^{2+} ). - Iodine’s Ionization:
Iodine (I) is a halogen located in Group 17 of the periodic table. Halogens typically gain one electron to achieve a stable electron configuration, forming anions with a 1- charge. Thus, iodine forms ( \text{I}^- ) ions. - Ion Charges and Balancing:
To form a neutral compound, the total positive charge must equal the total negative charge. Since calcium forms a ( \text{Ca}^{2+} ) ion and iodine forms an ( \text{I}^- ) ion, we need two iodine ions to balance the charge of one calcium ion. In this way:
- One ( \text{Ca}^{2+} ) ion provides a +2 charge.
- Two ( \text{I}^- ) ions provide a total of -2 charge. This results in a neutral compound, where the charges balance out, and the formula of the compound is ( \text{CaI}_2 ), which means that each calcium ion pairs with two iodide ions.
- Stoichiometry:
The simplest whole number ratio of calcium to iodine that results in a neutral compound is 1:2. Therefore, the correct formula is ( \text{CaI}_2 ).
Conclusion:
The formula for calcium iodide is ( \text{CaI}_2 ) because the calcium ion has a charge of 2+ and the iodine ion has a charge of 1-. To balance these charges, two iodine ions are needed for every calcium ion, resulting in the formula ( \text{CaI}_2 ). This reflects the principle of charge neutrality in ionic compounds.