Transition Metals: Melting Point and Conductivity HL Only
Quick Notes:
- Transition metals have partially filled d orbitals and delocalized d-electrons.
- Their properties include:
- High melting points: strong metallic bonding due to additional d-electron delocalization
- Excellent electrical conductivity: have mobile s- and d-electrons
- These properties result from stronger metallic bonds than those in s- or p-block metals.
- Chemical properties are explored in HL Reactivity 3.4.
Full Notes:
Transition metals have partially filled d orbitals and delocalized d-electrons.
What Makes Transition Metals Unique?
- Transition elements are defined as metals with an incomplete d sublevel in at least one of their oxidation states.
- They have both s- and d-electrons available for bonding.
- The d-electrons become delocalized, adding to the metallic bonding strength.
High Melting Points
Transition metals typically have high melting points due to:
- Greater electron density from d-electrons
- Stronger electrostatic attraction between cations and delocalized electrons
- Close-packed metal ions in a dense, rigid structure
Examples: Iron (Fe), Nickel (Ni), and Tungsten (W) all have very high melting points compared to s-block metals.
Electrical Conductivity
Transition metals conduct electricity well because they have delocalized electrons from both s and d orbitals.
- These electrons are mobile, allowing current to flow.
- Note: Not all d-electrons are delocalized, but enough are to enhance conductivity beyond s-block levels.
Linked Course Questions
Why is the trend in melting points of metals across a period less evident across the d-block?
In the d-block (transition metals), the trend in melting points is less regular compared to the s- and p-block elements because of the complex role of d-electrons in metallic bonding.
As you move across the period, 3d and 4s electrons can be involved in metallic bonding. However, the number of delocalised electrons doesn’t increase in a straightforward way, since d-electrons are added to inner orbitals and are partially shielded from the nucleus.
Also, as the d-subshell fills, the effective nuclear charge increases, pulling the outer electrons closer and reducing the ability of the atom to contribute to metallic bonding. At the same time, the metallic radius decreases, which can increase bonding strength — but these opposing effects don’t balance consistently across the series.
As a result, the strength of metallic bonding varies irregularly, so melting points rise and fall in a less predictable pattern across the d-block.
Summary
- Transition metals possess partially filled d subshells with d-electron delocalization that strengthens metallic bonding.
- High melting points arise from high electron density and strong electrostatic attraction in close-packed lattices.
- Excellent conductivity is due to mobile s- and d-electrons.
- Across the d-block, melting-point trends are irregular because d-electron participation changes in complex ways.