What is the correct name for the ionic compound CoF3?
The correct answer and explanation is:
The correct name for the ionic compound CoF3 is cobalt(III) fluoride.
Explanation:
Ionic compounds are named based on the metal and non-metal ions they contain. In this case, the metal ion is cobalt (Co) and the non-metal ion is fluoride (F), which is the ionic form of fluorine. The first step in naming this compound is determining the oxidation state of cobalt.
Cobalt can have multiple oxidation states, but in this compound, cobalt has an oxidation state of +3. The fluoride ion (F) carries a charge of -1. To balance the charges in the compound, three fluoride ions are required to pair with one cobalt ion, as follows:
- Cobalt ion: Co³⁺ (charge of +3)
- Fluoride ion: F⁻ (charge of -1)
Since three fluoride ions are needed to balance the +3 charge of cobalt, the formula becomes CoF₃. To indicate that cobalt is in the +3 oxidation state, the compound is named cobalt(III) fluoride. The number in parentheses after the metal’s name specifies the oxidation state, which is essential when dealing with transition metals like cobalt, which can have multiple oxidation states.
The naming convention for ionic compounds involves:
- Naming the metal (cobalt) first.
- Indicating the oxidation state of the metal (III for +3) in parentheses if the metal can have more than one oxidation state.
- Naming the non-metal ion (fluoride) by replacing the “-ine” ending of fluorine with “-ide.”
Thus, CoF₃ is cobalt(III) fluoride, reflecting its composition and the charge balance in the ionic structure.