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1.white phosphorus (I will use white p in my answer)
white phosphorus is a non-polar discrete molecule, the molecular formula is P4.
Its shape is pyramidal shape and with bond angle 60 degrees. The P atoms hold together by some PP single bonds. In each P atom, only 3 3p orbitals are used to form bonding. Since PP bond is non-polar, so the entire molecule is non-polar.
Therefore, P4 molecules interact with each other by weak van der waal's force (or instantaneous dipole-induced dipole interaction.
2. red phosphorus is also a non-pola discrete molecule, but the whole molecule is enormous. Its gigantic structure is produced by combining many P4 molecules (one PP bond in P4 is eliminated so as to form 2 bonds with 2 other P4 molecules). More generally, red phosphorus has a long straight chain. PP bond is non-polar, therefore the whole molecule is non-polar. The red P molecules hold together by means of instantaneous dipole-induced dipole interaction.
Because of the presence of weak van der waal's force, the melting point and boiling point of P is relatively lower than silicon, or even magnesium and sodium and aluminum. Since the molecular size of P is much smaller than the fundamental molecular size of S8, so P has lower melting point than sulfur.
In addition, phosphorus has higher melting point than chlorine and argon, because P has P4 structure, chlorine and argon are non-polar discrete molecule/atom. The interaction between P4 is much stronger than that between chlorine and that between argon.
2008-05-17 13:11:54 補充：
For the reactivity of P.
since white P has structure of P4, the bond angle is just 60 degrees, which is very small. Therefore, the repulsion between the P atoms in the molecule is very strong. So white P has very low melting point and boiling point.
2008-05-17 13:12:22 補充：
Normally, at room temperature and pressure, white P can ignite automatically. white P reacts with oxygen exothermically to produce an intense white light.
since red phosphorus has a relatively large molecular structure,
2008-05-17 13:12:32 補充：
the repulsion between the atoms is not so strong so that red phosphorus does not ignite automatically. But it will react with oxygen to produce an oxide without strong heating.
2008-05-17 13:12:38 補充：
There are 2 types of oxides of phosphorus when they react with oxygen.
P4O6 and P4O10. In very high temperature, a rare species, P2 is present in the phosphorus.
If you want to discuss the structure of P4O10 and P4O6 or want to discuss their chemistry. Tell me, I will ask you.
2008-05-19 17:07:48 補充：
the ans has been sent you through email
