✔ 最佳答案
1希望你有心機睇
2.以下的化學符號是代表atoms, eg H->hydrogen atom
為什麼Cl在ClO3中的ON是5?
原因是O比Cl搶電子的能力更強!!!
搶電子的能力有多強可參考electronegativity(out syl, 中六教)
http://en.wikipedia.org/wiki/Electronegativity
在這裡, 你只要記O比Cl搶電子更強
so you could imagine that O recieve e- from Cl
i.e Cl loses e-, so the ON for O and Cl are -2 and +1 respectively
(although ClO3 - is a polyatomic anion in which O and Cl are held by covalent bond, they are not actually "sharing" e-
e- tends to be shifted to the side of O)
the textbook said Cl has ON -1 at all time is incorrect.
IN MOST CASES, the ON for Cl is -1, but there are exceptions
而F是所有element中, 搶電子最強的
in OF2, the ON for O and F are +2 and -1 respectively
(Oxygen difluoride)
the higher the electronegativity, the higher the oxidising power and vice versa
the higher the electropositivity, .....
the ON for cation is the most easily to be regonized
eg. K+ must be +1,
Pb2+ must be +2,Pb4+ in PbO2 must be +4,
Fe3+ must be +3, Fe2+ must be +2
for the anion, the first thing you have to do is to find out which matter has the highest electronegativity(邊個搶電子最強, 做多幾條有經驗就ok架啦, 中五唔洗學electronegativity, 做多幾次就知O幾時都係-2 , 除左同F一齊)
in this case the power for gaining e- of O is higher than that of S
so you should start with giving ON for O = -2
3
it is a special case, memerize it
(the disproportionation reaction is required in the old syllabus)
consider the structure of H2O2
HOOH
(e- from H, e- from O)(e- from left O, e- from right O)(e- from H, e- from O)
in the middle of two O, since they are the same element, e- is neither attracted to the left or to the right, so e- is in the middle
so left O "gain" 1 e- from left H and right O.....
the disproportionation of H2O2:
2 H2O2----->2H2O + O2
see the ON for O, O is simultaneously being oxidised and reduced, we call is disproportionation
the production of chlorin bleach is also a disproportionation reaction
2008-03-28 01:08:41 補充：
at last, i know you are good at imagine, but somehow you should use more sense in imagination
electronic arrangement for K is 2,8,8,1
suppose ON for K is +5, it will lose 1e- in the 4th shell(possible) and 4e- in the 3rd shell(not possible)
suppose ON for H is +2, where does this +2 charge come from??
2008-03-28 01:08:57 補充：
H has only one proton(carry +1 charge)...even it loses its only single electron, it cannot give +2 charge
there are two e- in the outermost shell of O, so it may be able to gain two or one e-
O may lose 1e-, even 6e-(imagination), but 7e- is even over-imaginative=.=
2008-03-28 01:09:03 補充：
(from my chem knowledge, O can "lose" up to 2e-)
you may seeOxidation states at the right hand side
http://en.wikipedia.org/wiki/Oxygen
