chemical properties
As already mentioned, since the halogens are very active elements, they occur either as diatomic molecules or in the form of their compound in nature. they are good oxidizing agents. They have -1 oxidation state in their stable compounds. All halogens, except flourine (it takes only -1 oxidation), can take several oxidation numbers from -1 to +7.
Halogens, after the noble gases, have the secound greatest ionization energies. the activity order of halogens is F>Cl>Br>I. A more active halogen eliminates a less active halogen from its compounds. That means an active halogen oxidizes the other -1 charged halogen ion into elemental form.
Halogens, having diatomic structure, are oxidized in strong base solution, except F2.
Their compounds with hydrogen are acidic. Since HCl, HBr and HI dissolve and dissociate well in water (all except HF), they are known as strong acids. Among these, HCl is a well-known and frequently used acid. Although HI is stongest of all, it is not stable at hight temperature and it dissociates immediately into its elements.
some chemical reaction of halogens are given below.
1. A more active Halogens eliminates a relativity passive halogen from its compounds.
Br2 (l) + 2Nal(aq) ===> 2NaBr(aq) + I2(s)
Cl2(g) + 2KBr(aq) ===> 2KCl(aq) + Br2 (l)
a. when chlorine gass is passed through the test tube (on the left) containing Br- ions, bromine is reduced and bromine water is formed (in the middle), calor change can be observed more cleary in an organic solvent (on the right).
b. when chlorine gass is passed through the tube (on the left) containing I- ions, iodine is reduced and iodine water is formed (in the middle). color change can be observed more cleary in an organic solvent (on the right).
2. They produce acids by reacting with H2. These acids are called as halo acids.
H2(g) + F2(g) ===> 2HF(g)
H2(g) + Cl(g) =light=> 2HCl(g)
in the table 1. some physical properties of halo-acide are given.
since the halo-acids do not have an ionic structure, they do not conduct electricity. However, their ionic solutions are produced by dissolving them in water. HF is a weak acid and its ionization precent (α) is very low. theremore, it is weak electrolyte. The strength order of halo-acids is as given HF<HCl<HBr<HI
HF(aq) <===> H+(aq) + F- (aq) α =9.0
HCl(aq) ===> H+(aq) + Cl- (aq) α = 92.6
HBr(aq) ===> H+(aq) + Br- (aq) α = 93.6
HI(aq) ===> H+(aq) + I- (aq) α =
95.0
3. Halogens form compounds between each other
Cl2(g) + F2(g) ==2000C==> 2ClF (g)
Equal volumes chloro
fluoride
Cl2(g) + 3F2(g) ==2800C==> 2ClF3
(g)
Excess chloro trifluoride
Cl2(g) + Br2(g) ==00C==> 2ClBr (g)
chloro
bromide
in the table, the compounds formed between the halogens are given. the halogens are given. the halogens caryying +1 change have lower electronegativity, those carrying -1 charge have higher electronegativity.
