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Name: Alawi
Status: student
Grade: 9-12
Country: United Kingdom
Date: November 2008


Question:
What is the relationship between melting point and atomic radius?



Replies:
Alawi,

Melting point trends of atoms is very complex and can not be correlated to atomic radius alone. There are several reasons for this. (1) Across a periodic table row (where atoms become smaller as you go from left to right), the type of interatomic bonding changes from the relatively weak metallic bonds to that of network covalent bonds and then to weak diatomic molecule interactions - thus, because the type of bonding changes, the melting points can not be directly related. (2) Down a periodic table group (where atomic radii get larger and one might expect similar intermolecular interactions) the complications happen when access to the d-orbitals are involved and the shielding effect of electrons change. So really, the only group that can be trended is that of the alkali metals and the network covalent group of C (we can not even trend the alkaline earth metals) where as the atoms get larger, the melting points get smaller and this can be related to the inter-nuclei distances, and the compactness of the crystal lattice.

Greg (Roberto Gregorius)



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