why is the melting point of aluminium higher than sodium

The melting and boiling point of a substance is largely determine by the intermolecular forces which hold its molecules together. These may included Van der. The melting and boiling point of a substance is largely determine by the intermolecular forces which hold its molecules together. These may included Van der Waals forces (dispersion forces), dipole-dipole interactions, as well as hydrogen bonding. The stronger these forces act between molecules, the high the melting point and boiling point of the substance.


In this case with aluminum and magnesium, aluminum would have a higher melting point because the forces act stronger.
The reason why Al (Ne] 3s^2 3p^1) has the higher mp than Na is because all the valence eв participate in band formation and bonding. The 3p band. The reason why Al (Ne] 3s^2 3p^1) has the higher mp than Na is because all the valence eв participate in band formation and bonding.


The 3p band overlaps with the 3s band and results in strong bonding. And yes it does to some extent on the close packing nature of Al (Al is ccp with 12:12 coord). In Na ([Ne] 3s^1) only the 3s band is important and is bcc (8:8 coord) and hence bonding is weak: fewer eв in the bonding band MOs and Na can be cut with a plastic knife. The reason why metals such as W are strong is that are a whole bunch of d eв to contribute to band formation and bonding, and the bands are approximately only half occupied and hence strongly bonding.


On the other hand, the reason why Cu, Ag, and Au ([ ] nd^10 (n+1) s^1) are so soft is because the d band is full (equal number of bonding and antibonding eв) and contributes little to the bonding. It is the ns band that is responsible for bonding and like the group 1 metals the metallic bonding is weak.

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