The compounds AlCl3, CrCl3, and ICl3 have similar formulas, yet each follows a different set of rules to name it. Name these compounds, and then compare and contrast the nomenclature rules used in each case.
The Correct Answer and Explanation is:
The compounds AlCl3, CrCl3, and ICl3 all have similar chemical formulas, but their nomenclature rules differ due to the nature of the metal ions involved, especially the oxidation states of the metals. Here’s how each is named and the reasoning behind it:
- AlCl3: This is named Aluminum chloride.
- Explanation: Aluminum (Al) is a Group 13 metal that always forms a +3 oxidation state in compounds. The metal has a fixed charge, so we simply use the metal name followed by the non-metal (chlorine) with the “-ide” suffix. Since aluminum’s charge is constant, no Roman numeral is needed in the name.
- CrCl3: This is named Chromium(III) chloride.
- Explanation: Chromium (Cr) is a transition metal, and it can have multiple oxidation states. In this compound, chromium has a +3 charge. To indicate the oxidation state of chromium, we use a Roman numeral in parentheses after the metal name. Thus, the compound is named Chromium(III) chloride to show that chromium is in the +3 oxidation state.
- ICl3: This is named Iodine trifluoride.
- Explanation: Iodine (I) typically forms a -1 charge, and in ICl3, it is in the +3 oxidation state. In this case, the element iodine is named as the central atom, followed by the non-metal, chlorine, with a prefix “tri-” to indicate that there are three chlorine atoms. The name is Iodine trifluoride because of the naming convention used for nonmetals, where we use prefixes (mono-, di-, tri-) to indicate the number of atoms in the compound.
Comparison of Naming Rules:
- AlCl3: The name is straightforward because aluminum always has a +3 charge, so no Roman numeral is needed.
- CrCl3: Since chromium can have multiple oxidation states, the Roman numeral system is used to specify its +3 charge.
- ICl3: Iodine follows the rule for nonmetals where prefixes are used to denote the number of atoms in the molecule, and no Roman numeral is needed for iodine.
Each of these rules reflects the different types of elements and their behavior in compounds. Transition metals, like chromium, require Roman numerals for their variable charges, while main-group metals and nonmetals like aluminum and iodine follow simpler naming conventions.
