[mana]

hi guys
I have read in Silberberg general chemistry that in the periodic table the acidic character increases from left to right, but due to this table, it shows Mn, Tc and Re are exceptions, I wonder why?
can anyone explain?

[chenbeier]

This not really true, manganese has oxidation number from +2  in 1 steps until + 7
The oxids MnO, Mn2O3 are alkaline ,MnO2 amphother, the higher oxidations numbers have acidic behavour. This can be found also in 6 group  like Chromium. CrO, Cr2O3 and CrO2 is alkaline, CrO3 is chromic acid.

[mana]

This not really true, manganese has oxidation number from +2  in 1 steps until + 7
The oxids MnO, Mn2O3 are alkaline ,MnO2 amphother, the higher oxidations numbers have acidic behavour. This can be found also in 6 group  like Chromium. CrO, Cr2O3 and CrO2 is alkaline, CrO3 is chromic acid.

thank you for your answer, thus you mean I can't say which elements are acidic or which one is basic confidently, some oxides of one element such as Mn are amphoteric while the other oxides of Mn are acidic, am I right?

[chenbeier]

Correct.  You can say less oxygen or small oxidations number normaly has alcaline behaviour. Higher oxygen and larger oxidations number higher then 4 has acidic behaviour.