Transition metals are central to IB Chemistry Topic 13 (HL), but even SL students encounter their key properties. They sit in the d-block of the periodic table and display unique and useful chemical behaviors such as forming colored ions, acting as catalysts, and having variable oxidation states. Understanding transition metals helps students connect electron configuration, bonding, complex ions, and industrial chemistry.
What Are Transition Metals?
A transition metal is an element that forms at least one stable ion with a partially filled d-subshell.
This is the IB definition and it is essential to memorize.
Examples:
- Fe²⁺ has a 3d⁶ configuration → partially filled → transition metal
- Cu²⁺ has a 3d⁹ configuration → partially filled → transition metal
This definition excludes zinc, cadmium, and mercury because they form ions with filled d-subshells (d¹⁰), even though they are located in the d-block.
Where Are Transition Metals on the Periodic Table?
They occupy the central block of the periodic table:
- Groups 3 to 12
- Periods 4, 5, and 6
The most common ones in IB questions include:
- Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn
Certain heavy transition metals also appear, such as Ag and Pt.
Electron Configuration of Transition Metals
Transition metals fill the 3d, 4d, or 5d subshells depending on their period.
Example (Period 4):
- Sc: [Ar] 4s² 3d¹
- Ti: [Ar] 4s² 3d²
- Cr: [Ar] 4s¹ 3d⁵ (exception)
- Cu: [Ar] 4s¹ 3d¹⁰ (exception)
The exceptions for chromium and copper arise because half-filled and fully filled d-subshells are more stable.
Key Properties of Transition Metals (IB Required)
Transition metals share several characteristic chemical properties:
1. Variable Oxidation States
Transition metals commonly form ions with different charges.
Examples:
- Fe²⁺ and Fe³⁺
- Cu⁺ and Cu²⁺
- Mn has oxidation states from +2 to +7
This occurs because energy differences between 4s and 3d electrons are small, so metals can lose different numbers of electrons.
2. Formation of Colored Ions
Most transition metal ions are colored due to:
- d-electron transitions
- Splitting of d-orbitals in a ligand field
- Absorption of specific wavelengths of light
Examples:
- Cu²⁺: blue
- Fe³⁺: yellow/brown
- Ni²⁺: green
- MnO₄⁻: purple
Color changes are commonly tested in IB exams.
3. Complex Ion Formation
Transition metals form complex ions with ligands such as:
- H₂O
- NH₃
- Cl⁻
- CN⁻
Example:
[Cu(H₂O)₆]²⁺
[Fe(CN)₆]³⁻
This occurs because metal ions have:
- High charge density
- Empty d-orbitals
- Ability to accept lone pairs
Complex ion chemistry is a crucial part of HL material.
4. Catalytic Properties
Transition metals make excellent catalysts because they can:
- Change oxidation states easily
- Offer surfaces for adsorption and reaction
Examples:
- Fe in the Haber process
- Ni in hydrogenation of alkenes
- MnO₂ decomposing hydrogen peroxide
Catalysis is a real-world application of d-block chemistry.
Physical Properties of Transition Metals
Transition metals also share physical characteristics:
- High melting points
- High density
- Good electrical conductivity
- Strong metallic bonding
These arise from the presence of delocalized d-electrons.
Why Transition Metals Are Important
Transition metals are essential in:
- Catalysts
- Alloys
- Biological systems (e.g., heme with Fe²⁺)
- Batteries
- Industrial processes
- Pigments and dyes
- Coordination chemistry
Their combination of variable oxidation states and complex ion formation makes them uniquely versatile.
Common IB Misunderstandings
“All d-block elements are transition metals.”
Not true—Zn, Cd, and Hg do not meet the IB definition.
“Color always means transition metal.”
Many exceptions exist; the color must come from d-d transitions.
“All transition metals show the same oxidation states.”
Different metals show different ranges based on electron stability.
“Only HL students need to know transition metals.”
SL covers basic properties; HL covers complex ion theory in depth.
FAQs
Why do transition metals form colored compounds?
Because splitting of d-orbitals allows electrons to absorb visible light and transition between energy levels.
Why do transition metals have variable oxidation states?
Because 4s and 3d energy levels are close, allowing flexible electron loss.
Why are transition metals good catalysts?
They can adsorb reactants and change oxidation states to facilitate reactions.
Conclusion
Transition metals are d-block elements that form ions with partially filled d-subshells. They exhibit variable oxidation states, form colored ions, create complex ions with ligands, and act as catalysts. These properties make transition metals some of the most important and interesting elements in chemistry, both for IB studies and in real-world applications.
