question on chemistry on periodic table group1 and 2

1)As the atomic number increases down the group.
The elements at the buttom has more electron shell than the elements above.
While the elements at the buttom have more electron shell.
It means that the distance between the nucleus and the outermost electron is bigger.
So the attraction force between them is weaker, and the outermost electron is easier to escape.
When the outermost electron is easier to escape.
The element is easier to react with other substances.
Therefore the reactivity increase down the group.
Li,Na,K,Rb,Cs,Fr

2)Magnesium oxide has a much higher melting point than sodium chloride.
Because the ios of magnesium oxide carry 2+ charge.
It need more energy to seperate them then the ions (Na+ & Cl-) of NaCl which both carry 1+ charge.
Also the density of MgO per L is higher than NaCl.
That means the same energy is used to heat up more MgO.
So at the same temperature, less energy is recieve by each ion of MgO.
Therefore Magnesium oxide has a much higher melting point than sodium chloride.

3) Na+ and Mg2+ have same number of electrons (10 electrons ).
Na+ and Mg2+ are positive charged.
~> K+ & Ca2+
~> Li+ & Be2+
~> Rb+ & Sr2+
~> Cs+ & Ba2+
~> Fr+ & Ra2+
~> Na+ & Al3+

~> O2- & F-
~> S2- & Cl-
~> As3- & Br-
......

2008-02-03 00:16:59 補充：
Both Na and Mg2 obtained a octet structure.

Since for group 1 metals which has more shells, the outer most shell electron would be further away from the nucleus and the attractive force from the protons are weaker.
Therefore, the electron on the outermost shell is more likely to be lost, giving the metal a higher reactivity.

As Mg ion is 2+ and oxide ion is 2-, the amount of electrostatic attraction is twice larger than that between that between Na ion (1+) and Cl (1-). Since the attraction is harder to break, therefore the melting point of MgO is much higher

Both Na+ and Mg2+ have 2 completely filled electron shells
Two other examples are Al3+ and F-