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Explain why magnesium has a higher melting point than sodium

Hi for this question I wrote that magnesium has a smaller ionic radius than sodium so stronger attraction between nucleus and outer shell electrons - But in the mark scheme there wasn't this point so does that mean I don't get a mark of this Answer ?

Thanks

Reply 1

jamesgillian123

does the mark scheme mention nuclear radius?

Reply 2

RPatel365

If it doesn’t say it in the mark scheme you won’t get the mark.
I would say:
Mg2+ has a greater charge than Na+, therefore a greater number of delocalised electrons, therefore stronger metallic bonds.

Reply 3

CRTGG

Original post by GoodStudent 1710

The attraction is not between the outershell electrons and the nucleus.

Magnesium's metallic bonds are stronger than Sodium's. A metallic bond is the electrostatic attraction between positively charged ions and its of sea negatively charged delocalised electrons.
Magnesium has 2 outer electrons compared to Sodium's 1. Therefore it releases more electrons into the sea of delocalised electrons and it's nucleus has a greater positive charge of +2 compared to Sodium's +1. This means that Magnesium's nucleus has a greater attraction on the delocalised electrons. Stronger attraction = more energy required to overcome metallic bond.

(edited 6 years ago)

Reply 4

Pigster

Original post by CRTGG

A metallic bond is the electrostatic attraction between nuclei and its of sea negatively charged delocalised electrons.

It is the attraction between the delocalised e- and positive metal ions (cations). NOT the nuclei of the metals.

Reply 5

BTAnonymous

Well the highest occupied orbital is 3s in both Na and Mg so you can rule out electron shielding. It''s more to do with the fact that Mg exerts a greater electrostatic force on it's 'sea' of delocalised electrons because it's nucleus has a greater nuclear charge. Greater nuclear charge, stronger metallic bonds thus more energy is required to overcome the metallic bonds in Mg.

Thankssss

Original post by BTAnonymous

Greater nuclear charge, stronger metallic bonds thus more energy is required to overcome the metallic bonds in Mg.

No.

As I said earlier. It is not nuclear charge that matters, as the attraction is NOT between the nuclei and the delocalised electrons.

It is ionic charge that matters (or better to talk about charge density).