Why is sodium's melting point higher than potassium's?

[babbagee]

Element properties??

I needed some help with the following problem. I don't know what the question is asking me to do.

Breafly account for the following relative values:
a.) The melting point of sodium is 89^oC, whereas that of potassium is 63^oC

 

[GCT]

The different melting points suggest different strengths in intermolecular attractions (in this case btw the same elements). Both are on the same column. For sodium two 3s orbitals form a sigma molecular orbital while it is 4s for potassium. The 4s orbitals are more far away from the nucleus. Thus covalents bonds are weaker.

Another way to think about it is in terms of electronegativity. As one moves up the column the electronegativity increases, which suggests a greater effective nuclear charge.

Hope this answers your question.