Strength of Metallic Bonding and Melting Points
Specification Reference S2.3.2
Quick Notes:
- Metallic bond strength depends on:
- The charge of the metal cation
- The radius of the metal ion
- Stronger metallic bonds:
- Occur with higher charge (more delocalized electrons)
- Occur with smaller ionic radius (stronger electrostatic attraction)
- Melting point trends in the s- and p-block:
- Increase across a period (greater charge, smaller radius)
- Decrease down a group (larger ions, weaker attraction)
Full Notes:
What Affects the Strength of a Metallic Bond?
The metallic bond is the electrostatic attraction between positive metal ions and delocalized electrons.
Its strength depends on:
- Charge of the metal ion (cation)
More positive charge = more delocalized electrons = stronger bonding
Example Mg2+ has stronger bonding than Na+ - Radius of the metal ion
Smaller radius = electrons are closer to the nucleus = stronger attraction
Example Na+ is smaller than K+, so Na has a stronger metallic bond
Trends in Melting Points (s- and p-block Metals)
Across a Period (Left to Right)
- Melting points generally increase from Group 1 to Group 3 metals.
- Reason:
- Higher ionic charge
- Greater electron density (more electrons per cation)
- Smaller atomic radii
- Example Period 3: Na < Mg < Al
Al has the highest melting point due to 3+ charge and small radius.
Down a Group (Top to Bottom)
- Melting points generally decrease down Group 1 and Group 2.
- Reason:
- Increasing atomic radius
- Weaker attraction between cations and delocalized electrons
- Example Group 1: Li > Na > K > Rb > Cs
Summary Table: Factors Affecting Metallic Bonding
Factor / Trend | Effect on Bond Strength | Reason |
---|---|---|
Increased Cation Charge | Stronger | More delocalized electrons and higher electrostatic attraction to the electron sea |
Decreased Ionic Radius | Stronger | Electrons are closer to nuclei, increasing attraction |
Across a period (Group 1 → Group 3) | Melting point increases | Higher charge density and smaller radii |
Down a group | Melting point decreases | Larger ions reduce attraction to delocalized electrons |
Note
s- and p-block metals show clear trends based on simple electrostatic principles.
Transition metals follow more complex patterns due to d-electrons and variable oxidation states, and are not the focus here.
Summary
- Stronger metallic bonding results from higher cation charge and smaller ionic radius.
- Melting points generally increase across a period and decrease down a group in the s- and p-block.
- These trends follow from changes in charge density and electrostatic attraction within the metallic lattice.