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1.
The soft and hard classification of acid and alkali
On the basis of the acid-base electron theory, the acid-base is classified into soft and hard
.
Hard acid: The acid with small deformability of the electron cloud
.
Generally small radius, a high positive charge, such as H + , of Na + , of Mg 2 + , of Al 3+ , Si 4+ , of Cr 3+ , Mn 2+ , of Fe 3+ and the like
Soft acid: acid with large deformability of electron cloud
.
Generally large radius, low charge, such as a Cu + , of Ag + , of Cd 2+ , Hg 2+ , Hg 2 2+ , Tl + , of Pt 2+ and the like
Boundary acid: The deformability of electron cloud is between hard acid and soft acid, such as Cr 2+ , Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ , Zn 2+ , Sn 2+ , Sb 3+ , of Bi 3+ and the like
.
Hard alkali: alkali with small deformability of electron cloud
.
A large electronegativity electron atoms, lose electrons easily, such as F.
Soft alkali; alkali with large deformability of electron cloud
.
Feeding small electronegative atoms, easy to lose electrons, such as the I - , S 2- , the CN - , the SCN - , CO.
Base junction: deformability between the hard base and soft base, such as Br - , SO .
3 2- , N 2 , NO 2 - and the like
.
2.
Principles of combination of soft, hard acid and base
The principle of the combination of soft and hard acid and base is: soft and soft, hard and hard; soft and hard, unstable
.
The principle of soft-hard acid-base combination is very successful in explaining the stability of some complexes and the existence of elements in nature
.
For example, the order of stability of the complex is
The reason is Hg 2+ soft acids with soft bases I- bound complex is more stable; and of Al 3+ is a hard acid, hard base F.
- bound complex more stable
Ammonia can dissolve AgCl, Na 2 S 2 O 3 solution can dissolve AgBr, NaCN solution can dissolve Agl, and it can also be explained by the relationship between soft, hard and acid-base
.
Therefore, the order of stability is