2.3.2—Bond strength
- Syllabus
- First assessment 2025
- Objective
- 2.3.2
- Level
- HL
Metallic-Bond Strength
Metallic-bond strength depends on the attraction between metal ions and delocalized electrons. Ion charge, ion radius, and the number of delocalized electrons affect charge density and attraction.
A larger ion radius generally lowers attraction; greater charge or more delocalized electrons can strengthen metallic bonding. Use the stated comparison rather than a memorized trend alone.
Compare Na and Mg using the model: Mg supplies more delocalized electrons and forms smaller, more highly charged ions, giving stronger attraction and a higher melting point. State all relevant factors before predicting; across broader sets, lattice structure can prevent a perfectly smooth trend.
Comparing Metallic Strength
Assessment in practice
Representative question
Question 1
[Maximum number: 2]
Explain why the melting points of the group 1 metals (Li→Cs) decrease down the group.
2.
b
atomic/ionic radius increases
smaller charge density
OR
force of attraction between metal ions and delocalised electrons decreases
Marking guidance:
Do not accept discussion of attraction between valence electrons and nucleus for M2.
Accept "weaker metallic bonds" for M2.
The Metallic Model Summary
Retrieve the model: positive ions attract delocalized electrons; electron mobility explains conductivity and non-directional bonding explains malleability; charge, radius, and d-electron contribution explain strength trends.
A complete property explanation should name the cation lattice, delocalized electrons, and the specific structural change relevant to the property.