Melting point of Li

054690 · Posted: Wed Aug 03, 2005 11:12 am Post subject: Melting point of Li

Hi Guys, Li is the most metallic element in period 2,but it has the lowest melting point(120),as we move across the period there is a decrease in metallic charecter but the melting point increases.I would like to know why?

sdekivit · Regular Joined: 26 Jul 2005 Posts: 37 Location: Holland

think with me as we go from Li to B:

the charge of the ions as we go from Li to B ...... (increases/decreases)
The number of free valence electrons as we go from Li to B...... (increases/decreases)
Because of this, the bonding of the metalions will be.... (stronger/weaker)
That's why the melting point increases as we go from Li to B.

charco · Regular Joined: 07 Mar 2005 Posts: 96

FACT: the stronger the interparticular forces the higher the melting point as more energy is needed to separate the particles.

In metals the smallest particles are ions and they are held together by delocalised valence electrons (from the outer shell).

1. The greater the charge density of the positive ion (number of positives/volume) the greater the power of attraction of the ion.
2. The larger the number of valence electrons the more electron 'glue' there is to be attracted to the ions.

lithium has a small volume and only one valence elctron delocalised into the structure
beryllium has a smaller volume and has two valence electrons (per atom) delocalised into the structure
Consequently beryllium has a stronger structure than lithium

lithium has a small volume and only one valence elctron delocalised into the structure
sodium has a larger volume and only one valence elctron delocalised into the structure

The sodium ions have a lower charge density i.e. they are not so attracting as lithium
Consequently lithium has a stronger structure than sodium and a higher melting point

Hope this helps