[karnaty.rohit]

1.what do we mean when we say a certain oxide is more acidic than another oxide, basically what quantifies the acidic nature of oxides? why does acidity of oxides increase across the period from left to right and decrease down the group?

2.why does the acidity of group 5 and group 6 hydrides increase down the group? is there a connection between the acidity of hydrides and their reducing character as reducing character also increases down the group?

[DevaDevil]

Can you start a reasoning on your own? We will be able to help you along to get to the answer

[karnaty.rohit]

some thoughts which i have...
1. as long as i know acidity is compared by the ability to release H+(Bronsted definition) or the ability to accept a pair of electrons(Lewis definition). so is the acidity of oxides actually referring to the acids we get on hydrolysis?

2.  about this one the only thing i know is that the bond dissociation energy decreases down the group for the hydrides. what i felt was as a result H- is released easily down the group as it is a hydride(H has negative charge in it) but how does that increase acidity and reducing character?

[DevaDevil]

let us assume Bronsted for 1.:

1. In what cases can an oxide be an acid?
          - reacting with water to form an acid
          - neutralizing a base (reacting with a base to form water)
this is mainly valid for high-oxidation state metal oxides, which are represented most on the left and lower sides of the transition metal bloc.

2. Metal hydrides are usually basic. (you can write the simple reaction of a metal hydride with water yourself) Acidic hydrides are usually complexes (with carbonyl; HFe(CO)₄^- is such an example), but I do not know of any in group 5 or 6 to be honest.


Now if you are talking about old Group V and VI, then we can talk a bit, as in those groups the "hydrides" are actually protons (positively charged), which will probably alter your reasoning as well. Best to ask to make sure which is meant.

[karnaty.rohit]

ya i was referring to the old groups. for example the acidity and reducing character order for nitrogen group is NH3 < PH3 < AsH3 < SbH3 < BiH3. except for nh3 in all others hydrogen is more electro negative. is it a misconception that instead of a proton a negative H- is released in these cases?? and how does reducing character come into the picture?