S2.3.3 Transition elements and delocalized d-electrons (Higher Level Only) Notes

The Role of d-Electrons in Transition Metals and Trends in the d-Block

What Makes Metallic Bonding Unique?

1. In metals, valence electrons don’t belong to individual atoms.
2. Instead, they form a shared "sea of delocalized electrons" that move freely throughout the metallic lattice.
3. These electrons interact with positively charged cations, generating strong electrostatic forces known as metallic bonds.

1. For most metals, these delocalized electrons originate from the s-orbital of the outermost energy level.
2. However, in transition metals, electrons from partially filled d-orbitals also contribute to this electron sea.
3. This additional electron density significantly strengthens metallic bonds, setting transition metals apart.

The Impact of d-Electrons on Properties

The delocalized d-electrons in transition metals give rise to several key properties:

Higher Melting Points

1. The strength of metallic bonds depends on the density of delocalized electrons and their attraction to the metal cations.
2. Transition metals, with their additional d-electrons, form stronger metallic bonds than metals like sodium or magnesium.
3. This explains their generally higher melting points.

High Electrical Conductivity

1. The mobility of delocalized electrons makes metals excellent conductors of electricity.
2. In transition metals, the greater number of delocalized electrons (from both s- and d-orbitals) enhances this conductivity.
3. When a potential difference is applied, these electrons move freely, allowing electric current to flow.

Trends in the d-Block

The d-block elements (transition metals) exhibit fascinating trends in their physical properties, but these trends are often more complex than those observed in the s- or p-block elements.