Overview
This lecture covers the chemical properties of transition metals, especially their multiple oxidation states, and demonstrates how to determine oxidation states in various compounds.
Transition Metals: Chemical Properties
- Transition metals typically have multiple oxidation states, unlike main group elements.
- The most common oxidation state for many transition metals is +2.
- Multiple and stable oxidation states arise due to incompletely filled d orbitals.
- Loss of ns electrons occurs before (n-1)d electrons in transition metal ions.
Oxidation States and Rules
- Oxidation state indicates the degree of electron loss (oxidation) or gain (reduction) by an atom.
- The sum of oxidation numbers for a neutral compound equals zero.
- For polyatomic ions, the sum equals the ion’s charge.
- Elements in their elemental form have an oxidation number of zero (e.g., O₂).
- Halogens (like Br) typically have an oxidation state of –1.
- Oxygen usually has an oxidation state of –2 unless in peroxides.
- Polyatomic ions, such as CO₃²⁻ (carbonate), have fixed oxidation numbers (carbonate = –2).
Examples: Determining Oxidation States
- For CoBr₂: Br is –1; set up x + 2(–1) = 0 ⇒ x = +2 (Cobalt is +2).
- For ZnCO₃: CO₃ is –2; set up x + (–2) = 0 ⇒ x = +2 (Zinc is +2).
- For Ag₂S: S is –2; set up 2x + (–2) = 0 ⇒ x = +1 (Silver is +1).
- For MnO₄⁻: O is –2, four O atoms; set up x + 4(–2) = –1 ⇒ x = +7 (Manganese is +7).
Key Terms & Definitions
- Oxidation State — The hypothetical charge an atom would have if all bonds were ionic.
- Transition Metals — Elements with partially filled d orbitals, often displaying variable oxidation states.
- Polyatomic Ion — Charged species composed of several atoms bonded together (e.g., CO₃²⁻).
Action Items / Next Steps
- Review oxidation state rules and practice with additional example compounds.
- Refer to textbook section 4.2 for detailed rules.
- Create flashcards for oxidation state rules if needed.
- Complete assigned homework on oxidation numbers and electron configurations.