how does the basicity of amines(primary ,secondary ,tertiary)change if in aqueous medium?

2> in coordination compounds when to nomenclatae the compounds 'ammine' and when 'amine'?

Answers of your questions are as follow:

(1) The basicity of amines should decrease in the order:

3⁰ amine > 2⁰ amine >1^o amine >  NH₃

But it is found that in aqueous solution, 2⁰ amine is invariably more basic than 1^o and 2^o amine.

Order of basic strength in the case of methyl-substituted and ethyl-substituted amines is as follows:

The basicity of an amine  in aqueous solution depends upon the stability of the ammonium cation, which in turn depends upon a combination of the following three factors:

(1) +I effect of the alkyl group

(2) Extent of hydrogen bonding with water molecules.

(3) Steric effect of the alkyl groups

On the basis of +I effect, basicity of amines should decrease in the order,

3⁰ amine > 2⁰ amine >1^o amine >  NH₃

But if we look at the stability of ammonium cation, then cation derived from 1^o amine should be more stable because it can form more hydrogen bonds with water. Thus on the basis of H-bonding and steric factors, basicity of amines should decrease in the order:

1^o amine > 2⁰ amine > 3⁰ amine

From all this discussion, we may conclude that it is a combination of +I effect of the alkyl groups, H-bonding and steric factors which determine the stability of the ammonium cation.

So overall decreasing strength of methylamines is :

If however alkyl group is bigger than CH₃ group, there will be some steric hindrance to H-bonding. As a result, stability due to +I effect predominates over the stability due to H-bonding and hence  3⁰ amine becomes more basic than 1^o amine. In other words, overall decreasing strength of ethylamines will be:

(2) In coordination compounds, while naming them, 'ammine' is used when the ligand is NH₃.

For example:

IUPAC name of the compound [Co(NH₃)₆]ClSO₄ will be hexaamminecobalt(III) chloride sulphate

But when the ligand is substituted amine for example: ethylenediamine (NH₂CH₂CH₂NH₂) then we use word ' amine'.

For example: IUPAC name of [CoCl₂ (en)₂]SO₄ dichlorobis(ethane-1,2-diamine) cobalt(IV) sulphate.