1)explain the order of melting boiling point of alkyl halides?
2) explain the order of their solubility?
3)plzzz explain - how does alkyl halides having same alkylgroup decrease in the order ??
1) There are two kinds of attraction exist in between the molecules of alkyl halides.
i) Van der waal forces (london dispersion forces)
ii) Dipole-dipole attraction.
The strength of these forces depends on the size of molecule. Greater the size and number of electrons, larger will be the intermolecular force of attraction.However, the dipole-dipole attractions are permanent. The magnitude of dipole-dipole interactions depend on the polarity of C-X bond.
The Melting and Boiling points of alkyl and aryl halides increase with increase in the molecular size or molecular weight. Although the dipole-dipole interaction is same for all the alkyl halide carry same halogen moiety, the contributing effect is produced by van der waal force of attraction which depends on the size of the molecule. As the size increases, Van der waal force of attraction also increase. It requires more amount of energy to break the attractive force in between the particle in solid and liquid state hen melting and boiling point increases with increase in molecular size or weight.
In case of alkyl halide with same alkyl group and different halogen, melting and boiling point increases from alkyl fluorides to alkyl iodide. This is due to increase in the size of molecule with increase in the size of halogen atom.
In case of branching , the boiling points decrease with increase in the branching of carbon chain. . Boling points are more affected by branching than Melting points.The melting points are also affected by symmetry of the molecule. The symmetrical molecules fit better into the crystal lattice and hence possess higher melting points.
2) for solubility we follow the rule "Like dissolves like"
Alkyl halides are comparatively non-polar to water hence are insoluble in water. They are fairly soluble in non-polar solvents.
3) As the size of halogen atom increases, the size of its electron cloud also increases. Due to the increased cloud of electron, the possibility of induced dipole increases that will increase force of attraction in between the molecules hence higher in boiling and melting points. Therefore, an alkyl fluoride has a lower boiling point than an alkyl chloride with the same alkyl group. Similarly, alkyl chlorides have lower boiling points than alkyl bromides, which have lower boiling points than alkyl ioddes.