Overview
This lecture explains how to name compounds containing transition metals, focusing on charge determination, old vs. new naming conventions, and special exceptions.
Transition Metals: Location and Charges
- Transition metals (TM) are in the middle of the periodic table, between main group metals in groups 2 and 3.
- Main group metals form predictable charges: group 1 (+1), group 2 (+2), group 3 (+3).
- Many transition metals can form multiple charges (often two or three).
- Example: Copper forms +1 or +2; Cobalt forms +2 or +3.
Old vs. New Names for Transition Metals
- The old (common) name uses "-ous" for the lower charge and "-ic" for the higher charge (e.g., ferrous for Fe2+, ferric for Fe3+).
- The new (IUPAC) name uses the element's name with the charge as a Roman numeral in parentheses (e.g., iron(II), iron(III)).
- Both naming systems are still in use.
Naming Ionic Compounds with Transition Metals
- To determine the metal’s charge, use the charge of the anion and the number of each ion in the formula.
- The subscript of the anion becomes the cation's charge (crisscross method), and vice versa.
- Example: CuI₂ has two I⁻ ions; Cu must be +2 (copper(II) iodide or cupric iodide).
- For single ions, use either the new name with Roman numeral or the old name with the correct ending.
Polyatomic and Monoatomic Ions
- Most transition metal ions are monoatomic, except for special cases like Hg₂²⁺ (two mercury atoms bonded together).
Key Transition Metals to Memorize
- Eight transition metals form two different charges and require old/new naming systems.
- Four transition metals form only one charge: silver, nickel, cadmium, zinc.
Special Rules for Single-Charge Transition Metals
- Transition metals with only one charge do NOT use Roman numerals or old names (e.g., Ag⁺ is "silver ion," not "silver(I) ion").
Practice Examples
- Chromic bromide: Cr³⁺ and Br⁻ ➔ CrBr₃.
- Manganous selenide: Mn²⁺ and Se²⁻ ➔ MnSe.
- Nickel oxide: Ni²⁺ and O²⁻ ➔ NiO.
- Mercuric oxide (HgO): Hg²⁺ and O²⁻ ➔ HgO.
- Mercurous oxide (Hg₂O): Hg₂²⁺ and O²⁻ ➔ Hg₂O.
Key Terms & Definitions
- Transition metal (TM) — Element in the center of the periodic table capable of multiple positive charges.
- Old/Common name — Naming based on Latin roots with "-ous" (lower) and "-ic" (higher) endings.
- New/IUPAC name — Element’s name with Roman numeral in parenthesis to show charge.
- Monoatomic ion — Single atom with a charge.
- Polyatomic ion — Multiple atoms bonded together carrying a charge.
- Crisscross method — Method of assigning charges using subscripts in ionic formulas.
Action Items / Next Steps
- Memorize the list of eight transition metals with multiple charges and four with only one charge.
- Practice naming compounds and ions using both naming systems.
- Prepare a reference sheet with transition metal names, symbols, and possible charges.