Why the melting and boiling points of halogens increases in going from top to the bottom of the group?

All the halogens are diatomic molecules. The forces of attraction are weak Van der Waals forces. The strengths of these forces depends on the surface area which in turn depends on the molecular mass. Down the group, molecular mass and surface area increases, hence melting and boiling points increases down the group.
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Assign reason for the following:
Bismuth is a strong oxidizing agent in a pentavalent state.

The stability of + 5 oxidation state decreases down the group due two inert pair effect. So + 5 oxidation state of Bi is less stable than its + 3 oxidation state.
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Assign reason for each of the following:
Noble gases are mostly chemically inert.

Genral electronic configuration of noble gas is ns2 np6. Thus having stable coniguration.
Noble gases are mostly chemically inert due to the following reasons:
(i)    Atoms of the noble gases have stable closed shell electronic configuration.
(ii)    Noble gases have exceptionally high ionisation energies.
(iii)   Noble gases have very low electron affinities.

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NO is paramagnetic in the gaseous state but diamagnetic in the solid and liquid states. Justify?


NO has odd number of electrons (7 + 8 = 15) and due to the presence of unpaired electron, it is paramagnetic in the gaseous state.



However, in the liquid and solid states, the unpaired electrons are involved in the formation of loose dimer. In the absence of any unpaired electrons, it is diamagnetic in nature.
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(CH3)3 N is basic but (CF3)3 N is not basic. Explain.

Basicity can be account by the availbility of electron in case of (CH3)3 N there is more electron avaliable than (CF3)3 . This is due to different electronegativities of H and F bonded to nitrogen. In (CH3)3 N the lone pair of N is concentrated on N and so it can act as an electron pair donor (Lewis base). However in (CF3)3 N, the electron density on n is decreased due to strongly electronegative F atom attached to C. Hence it cannot act as a Lewis base.
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