Group 17 are collectively called as halogens (In Greek: halo means salt and genes mean producing, so collectively salt producing) and it consists of fluorine, chlorine, bromine, iodine and astatine. Halogens are highly reactive non-metals. These elements greatly resemble in property with each other. Similarity to this extent is not found in other groups of the periodic table. They have a regular gradation in the physical and chemical properties. Astatine is the only radioactive element in the group. They have seven electrons in their outermost shell (ns2 np5) and are short of one electron from the configuration of nearest noble gas. The chemical properties and reactivity of an element is determined by the oxidation state exhibited by them.
Chemical properties and oxidation state
All the elements of halogen family exhibit -1 oxidation state. However elements such as chlorine, bromine and iodine also show +1, +3, +5 and +7 state. This higher oxidation state of chlorine, bromine and iodine is realized when these halogens are in combination with small and highly electronegative atoms of fluorine and oxygen. The oxides and oxoacids of chlorine and bromine have +4 and +6 states. There are no valence shell d orbitals in fluorine atom and therefore it cannot expand its octet. Fluorine being the most electronegative element exhibits only -1 oxidation state.
Halogens are highly reactive, they react with metals and non-metals in order to form halides. Their reactivity decreases as we move down the group. Halogens have strong oxidizing properties. F2 is the strongest oxidizing halogen. It easily oxidizes other halide ions present in solution or in solid phase. In general, a halogen oxidizes halide ion which is of higher atomic number. For example:
F2 + 2X– → 2F– + X2 (X = Cl, Br or I)
From standard electrode potential, the decreasing oxidizing ability of halogen can be easily observed.
The relative oxidizing nature of halogens can be illustrated by their reactions with water. Fluorine oxidizes water to oxygen. Whereas chlorine and bromine react with water in order to form respective hydrohalic and hypohalous acids. Iodine reacts with water in a non-spontaneous way. I– can be oxidized by water in the acidic medium. For example:
4 I– (aq) + 4H+ (aq) + O2 (g) → 2I2(s) + 2H2O (l)
This article covers the properties and oxidation state of group 17 elements. For further query install Byju’s the learning app.
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