melting point and boiling point of metal

1. strength of metallic bond depends on
(1) no. of valence of electrons
(in this case, outermost delocalized e- in s orbital)
more outermost e-, stronger metallic bond

Reason: More electrons used to bind (attractively) the metallic cations
reduces the repulsion between metallic cations
and thus stabilizes the system.
=>More energy is supplied externally
to separate the metallic particles. (stronger bond)

(2) atomic radius
Smaller radius, stronger metallic bond

Reason: smaller radius makes
the nucleus of the metallic cation exert a larger force
to attract the outermost delocalized electrons.
=>More energy is supplied externally
to separate the metallic particles. (stronger bond)

2. For any kinds of bonding to be overcome,
if the bond is stronger, it needs more energy to separate
the stronger binded species effectively enough to change the state
(from solid to liquid and to vapour).

calcium atom has a SMALLER size and atomic radius than sodium atom
because calcium atom has a higher effective nuclear charge than sodium atom.
Also, calcium atom has 2 delocalized electrons
which is more than that (only 1) of sodium atom.

from the fact mentioned in question 1., it is not surprising that
calcium metal has higher melting and boiling point of sodium metal.

I hope this could help.

2007-12-08 23:06:03 補充：
Let us consider two factors. One is that sodium and calcium are in the same period and have the same number of inner shells.

2007-12-08 23:06:34 補充：
This indicates that the outermost shell electrons are shielded by the inner shells of SIMILAR repulsion strength from the attraction by the nucleus. This is known by shielding effect.

2007-12-08 23:07:06 補充：
Another one, in contrast, calcium atom has one more proton than sodium atom. calium atom exerts LARGER force to the electrons. This the factor of nuclear charge.

2007-12-08 23:07:24 補充：
After all, an apparent increase in nuclear charge from sodium to calcium offsets their similar shielding effects.

2007-12-08 23:07:50 補充：
The net effect, effective nuclear charge is the determining factor that reflects the attraction between the nucleus and the outermost electrons. As calcium nucleus exerts greater effective nuclear charge on their outermost electrons, the atomic radius and the size is smaller.

2007-12-12 01:42:25 補充：
sorry, follo26, I made a mistake.in this case, we cannot make a concise comparisionbetween the size of calcium and sodium.because down a group, atomic size increases

2007-12-12 01:42:58 補充：
while across a period, atomic size decreases due to the evaluation of effective nuclear charge.This is known as diagonal relationship.

Na and Ca are not in same period.......

2007-12-12 19:05:23 補充：
good u discover it