Boiling Point (Super Urgent!!)

Since there are weak van dar Waal's forces between the CCl4 molecules when compared with the stronger ionic bond between the Pb2+ ions and Cl- ions, so less energy are required to vaporize CCl4 and then has a lower boiling point.

There are both ionic bonds between Al2O3 and MgO. Al3+ ions has a higher charge density than Mg2+ ions, so the force between Al3+ ions and O2- ions in Al2O3 is higher than that between Mg2+ ions and O2- ions in MgO. Thus, more energy are required to vaporize Al2O3 and then has a higher boiling point.

2012-01-09 21:54:33 補充：
in fact,,,i think it is DSE/ALE questions...so don't be so theoretical

many references quoted melting points of many substances which would normally sublime, like CO2 and I2. considering this, one may assume that the "boiling point" is measured at elevated pressure... or they just extrapolate the trend and "calculate" the boiling points.

i think ans MUST inc. the structure...

PbCl4 has molecular strucutre instead of ionic structure. In other words, it exists as PbCl4 MOLECULES. If PbCl4 were ionic, the Pb^4+ would have a very large charge density and would than change back to molecular.

2012-01-04 19:56:14 補充：
The boiling point of PbCl4 is UNKNOWN. When PbCl4 is heated to 105°C, it explodes. Thus some books quote that the boiling point of PbCl4 is 105°C. Actually, this is NOT the boiling point of PbCl4.