Chlorine, bromine and Iodine form oxy acids easly due to less electronegative than oxygen but oxy acids of fluorine are unsatble due to high electronegativity only hypofluorous (HOF) acid is stable.
|
O.S of
halogens |
Name of
acids |
Name of salts |
fluorine |
Chlorine |
Bromine |
Iodine |
|
(+1) |
Hypohalous |
Hypohalite |
HOF |
HOCl |
HOBr |
HOI |
|
(+2) |
Halous |
Halite |
---- |
HClO2 |
---- |
---- |
|
(+3) |
Halic |
Halate |
---- |
HClO3 |
HBrO3 |
HIO3 |
|
(+4) |
Perhalic |
Perhalate |
---- |
HClO4 |
HBrO4 |
HIO4 |
Important
Note: All the
hypohalous acids (HXO) are unstable and readly form HXO3. Among the relative
order of stability is: HClO > HBrO > HIO
Relative
acidic strength of oxy acid Halogens:
(1) According to Bronsted
Lowery concept, a strong acid has weak conjugate base and vice
versa.
The
given oxy acids of chlorine HCIO, HCIO2, HClO3 and HClO4 and their conjugate
bases are CIO-,
CIO2-, ClO3-, ClO4- respectively. These
anions are stabilised to greater extent, due to the presence of π-bond and lone
pair, if number of π-bond increase extent of stabilisation increase. In case
of ClO- there is no π-bond
hence if form less stable conjugate base hence act as weak acid while in case
of ClO4- it has three pπ-dπ bond which stablised
greater extent and form more stable conjugate base hence it conjugate acid
(HClO4) is strongest acid. Oxy acids of chlorine and their number
of pπ-dπ
bonds given
as:
HOCI
(0=Pπ-dπ bond)
HOCIO
(1=Pπ-dπ bond)
HOClO2 (2=Pπ-dπ
bond)
HOCIO3 (3=Pπ-dπ
bond)
Thus
overall order of acidic strength of oxy acids of chlorine is as:
Acidic srength of acid as
: (HClO) < (HClO2)<(HClO3)<(HClO4)
(2) In general the relative strength of
oxy acid can pridicted on the basis of electronegativity
and oxidation state of central non
metal atom.
(1) For given oxy acid on increasing of electronegativity
acidic strength increses for example perchloric (HClO4) is stronger
acid than perbromic acid(HBrO4), which should be a stronger acid than
periodic acid (HIO4) because the electronegativity of the central
atom increses as (Cl>B>I).
Acidic srength of acid as :
(HIO4)<
(HBrO4)<(HClO4)
(2) For given non metal oxy acid the
strength of oxy acid increases as the oxidation state of central atom increases
for example; "HClO (+1),HClO2(+3), HClO3 (+5),
HClO4(+7)
Acidic srength of acid as :
(HClO)< (HClO2)<(HClO3)<(HClO4)
Relative
oxidizing character of oxy acid of Halogens:
Hypochlorous
(HClO) act as the best oxidizing agent because it give nascent oxygen easily.
HClOàHCl + O (nascent oxygen)
Order of oxiding character: (HClO4)<(HClO3)<(HClO2)<(HClO)
Relative
thermal stability of oxy acid of Halogens:
As the
number of pπ-dπ bond incrases
bond strength incrases and thus order of thermal stability also increases.
Thermal stability order: (HClO)< (HClO2)<(HClO3)<(HClO4)
Relative
(Cl-O) bond order and bond length
HOCI (0=Pπ-dπ bond) BO=1
HOCIO (1=Pπ-dπ
bond) BO=1.5
HOClO2 (2=Pπ-dπ
bond) BO=1.66
HOCIO3 (3=Pπ-dπ
bond) BO=1.75
Hence (Cl-O) single bond length order as: (HClO)>(HClO2)>(HClO3)>(HClO4)
Question: which set of properties follow given order:
(HClO)< (HClO2)<(HClO3)<(HClO4)
(i) Acidic nature
(ii) Oxidizing nature(iii) Thermal stability (iv) Cl-O single bond
(A)
Only (i) (B) Only (i) & (iii) (C) Only (i), (iii) & (iii) (D) All of these
Answer
Key: (B)
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