Melting Points of Alkali Metals.?

Question

I got stuck on one problem and it's about the melting points of the Alkali Metals. I have to explain why the melting point of alkali metal decrease down the group: Li to Cs. The book said that the bigger the molecule is, the higher the London dispersion, therefore resulting in higher intermolecular forces, finally to higher melting point. But then Alkali metal is opposite of what the book said... Why is that? I don't know how to answer it, please help me! (I already posted another question regarding this but I guess I worded the question weird, so I am posting another question.) Thank you!

Answer 1

I answered this question on your other "question". It has to do with the nature of bonds. Solid elemental metals are not held together by london dispersion forces, they are held together by metal-metal bonds which are like covalent bonds. Its a different type of interaction, and leads to a different behavior.

http://answers.yahoo.com/question/index;_ylt=AtcyydTOFhEAKAu9kJ9WoL_sy6IX?qid=20061228183951AAMKsKB

Answer 2

From http://www.wpbschoolhouse.btinternet.co.uk/page07/sblock.htm

Generally (but not always), the melting and boiling points fall steadily [with increasing atomic no]:

This is because the ionic radii increase down the group increasing charge separation between the metal cations of the lattice and the free delocalised electrons. This weakens the electrical attractive bonding force and so less thermal KE is needed to weaken the lattice to the 'collapse point' i.e. melting. BUT the situation is not as simple as might be expected, e.g. the metal ions do not always have the same crystal lattice packing arrangement.

Answer 3

The hallogens are non-metals and metalois so there melting points are lowere than the alkali metals

Answer 4

Find a copy of a detailed periodic table and it wil tell you specific data on boiling and melting points of the alkali metals.....