Which element is more reactive

Your question is concerned with the strength of metallic bonds. Hence, I just quote what I have answered:
The strength of metallic bonds depends on(1) the number of outermost shell e- involved in forming metallic bonds [for Na only 1 e- and for Al 3 e- ](2)the size of the metal atom. The smaller the size, the closer is the distance between nucleus and the outermost shell e- . The greater attraction between the e- and nucleus, the higher will be the b.p. and m.p. of the metal. The size of the atom is governed by the effective nuclear charge. When moving across the period, the screening effect due to the outermost e- is poor.(注意,因為是across the period,所以 screening effect 才poor)The increasing effective nuclear charge across the period attracts the outermost shell e- firmly. Hence the atom size contracts.
For (1) sodium, it has only 1 outermost shell e- while (2) calcium has 2 outermost shell e- comparing sodium. Hence the metallic bond of Ca is stronger than Na. This signifies Ca is more difficult to lose an e-.
You may think that the size of sodium is smaller than calcium. The attractive force generated between nucleus and outermost shell e- may be stronger. However, for calcium, it has 20 protons comparing sodium just 11 protons. Hence, the attractive force generated between nucleus and outermost shell e- due to calcium nucleus should be stronger. As a result, Na is more reactive than Ca.
I hope you will find them helpful.


2008-01-16 21:33:28 補充：
Besides Ca can use 3-d orbital to take part in the metallic bond while Na can't. Hence the number of electrons involved in forming metallic bond will be greater in Ca than Na.

2008-01-16 21:33:39 補充：
The more the electrons involved in forming metallic bond, the stronger is the metallic bond. And the more difficulty of the metal to lose electrons.

2008-01-18 16:30:15 補充：
Calcium atom is larger than sodium due to having one more shell. For sodium just has K, L and M shells (2,8,1), while calcium has K,L, M and N (2,8,8,2).

2008-01-18 16:30:26 補充：
The nuclear charge of Ca must be greater than Na due to 20 protons attract 2粒 outermost shell electrons comparing Na with 11protons attract 1粒 outermost shell electron.

according to the reactivity series, sodium is more reactive
the first five metals in the reactivity series in desencding order are:
| potassium more reactive
| sodium
| calcium
| magnesium
| aluminium less reactive
V

Explanations:
in the same period and from group I to 0, there is an decrease in the reactivity
because from group I to 0 , the no. of electrons in the outermost shell increase
(for example sodium and magnesium, which are in the same period, sodium has 1 electron in the outermost shell and magnesium has 2)
it takes more energy for more electrons to lose from the outermost shell
so the reactivity decrease from group I to 0

in the same group form period 1 to 7
there is an increase in the reactivity
it is because the larger the period , the more the outermost shell
that mean the outermost shell electrons is more and more far away from the nucleus, so it can lose easily and thus the reactivity increase form period 1 to 7

Sodium is more reactive than Calcium

There is a pattern, for elements in Group I and II,
they are arranged in increasing reaction down the group,
which means that for example in Group I of the Periodic table,
Cs is the most reactive, while Li is the least reactive in group I.
This is because the electron cloud of Cs is bigger than Li,
so the outermost electron of Cs is well shielded from the nucleus,
the nucleus exerts a smaller attraction force on the valance electron in Cs than that in Li,
Thus, the valance electron in Cs will be easily removed and react with other elements or compounds

When comparing sodium and calcium,
as Calcium has an electronic configuration of 1s(2) 2s(2) 2p(6) 3s(2) 3p(6) 4s(2),
the 4s orbital is fully filled by electrons which provides extra-stability by Hunds' rule,
That's why the outermost electron of sodium is easier to be removed than that in Calcium and become more reactive.

1.)Sodium is more reactive.
2.)...... I don't know......
3.)According to the periodic table,Sodium has a higher position than Calcium,therefore,Sodium is more reactive than Calcium.
4.)Same as no. 3