Electronic configurations Questions

Explain the oxidation states of CI, in terms of its electronic configuration.

Ans : Chlorine has only one-electron less than the next noble gas. Therefore, it can get the noble gas configuration either by gaining one electron to form uninegative ion, Cl or by sharing electrons with other atom. Thus, it shows an oxidation state of -1 or + 1.

Chlorine also show positive oxidation states of + 3, + 5 and + 7 due to the presence of empty d-orbitals in its valence shell. As a result the outer s- or p- electrons can easily be promoted to the vacant d-orbitals as shown below.

State of chlorine atom Electronic configuration Oxidation states
Ground state 3s23p53d° -1 or+1
First excited state 3s23p43d1 +3
Second excited state 3s23p33d2 +5
Third excited state 3s13p33d3 +7

Give the reaction of Cl2 with the following

(i) S02 (ii)NaOH (iii) Iron metal

Ans : (i) Reaction with SO2

CI2 when reacts with SO, underthe influence of sunlight and gives SO, CV (sulphury! chloride).

(ii) Reaction with NaOH :

a) When chlorine reacts with cold, dilute NaOH gives sodium chloride and sodium hypochlorite(NaOCI).

CI2 + 2NaOH NaCI + NaOCl + H20

b) When chlorine reacts with hot, concentrated NaOH gives sodium chloride and sodium chlorate (NaCI03)

3CI2 +6NaOH 5NaCl+ NaCIO3 +3H2O

(iii) Reaction with iron metal:
Chlorine reacts with iron metal and gives ferric chloride(FeCI3).
3Cl2+2Fe 2FeCI3

Write the names and formulae of oxoacids of CI2

Ans : Oxoacids of chlorine

Name Formula
Hypochlorous acid HCIO
Chlorous acid HCIO2
Chloric acid HCIO3
Perchloric acid HCIO4

How does F2 react with (i) H20 (ii) NaOH. Give equations for them.

Ans : (i) Reaction with H2O :

F2 reacts with water and gives ozonized oxygen.

2F2+2H2O MHF +O2

3F2+3H2O 6HF+O3

(ii) Reaction with NaOH

a) When F2 reacts with cold, dilute NaOH gives sodium fluoride and oxygen diftuoride (OF2)

2NaOH + 2F3 2NaF + OF2 + H20

When F, reacts with hot, concentrated NaOH gives sodium fluoride and oxygen.

4NaOH + 2F2 4NaF+ O2+2H20

What is “Available chlorine” ? Give chtirriicaf equation(s) which determine the same.

Ans : “Available chlorine” is the amount of Cl2 set free when bleaching powder is treated with excess of dilute H2SO2, orCO2

A good sample of bleaching powder contain about 35-38% available chlorine.

CaOCI2 + H2SO4 CaSO4+H2O + Cl2
CaOCl2+CO2 CaCO3 + Cl2
What are the different classes of Interhalogen compounds

Ans : Halogens mutually combine together to form a set of compounds of general formula AXn where both A and X are halogen atoms and n = 1, 3, 5 or 7. These compounds are called interhalogen compounds.

In the general formula AXn of interhalogen compounds, A is always a larger halogen atom, whereas X is always a smaller halogen atom.

The oxidation states ofthe halogen atom A could be +1, + 3, + 5 or + 7, but the oxidation state of the halogen atomX is always -1.

Depending upon the value of n, interhalogen compounds can be classified into the following four categories.













  ClF BrF, BrCI, ICI  

CIF3 . BrF3


BrF5. IF5



Name the hybridizations occuring in the interhalogen compounds.

Ans : (i) Interhalogen compounds ofthe type AX are consists ofthe two halogen atoms linked together through a single covalentbond.
Ex; CI –F

(ii) Interhalogen compounds ofthe type AX2 possess a T-shaped structure and are formed by sp¬¬3d hybridisation of the central atom A in its first excited state.
Ex: CIF3

(iii) Interhalogen compounds ofthe type AX5 have square pyramidal structure and are formed by sp3d2 hybridisationofthe central atom A in its second excited state.
Ex: BrF5

(iv) The only known interhalogen compound ofthe type AX7, i.e., IF7 is formed by sp3d3 hybridisation ofthe centra! iodine atom in its third excited state. The molecule has a pentagonal bipyramidal structure.

Write the names of all the VIIA group elements.
Ans :





















List out the atomic numbers and the corresponding electronic configurations of halogens

Ans :




Atomic number


Electronic configuration






[He] 2s22p5


CI 17 [Ne] 3s23p5


Br 35 [Ar] 3d104s24p5


1 53 [Kr] 4d105s25p5


At 85 [Xe] 5d104f46s26p5


Mention the most electronegative element in the periodic table. What is the electronegativity value of F3

Ans : Fluorine is the most electronegative element in the periodic table. Electronegativity value of fluorine is 4.0 (on pauling scale)

Name the element with highest E.A. and gnrelfs value.

Ans : Chlorine is the highest electron affinity element in the periodic table.
Electron affinity value of chlorine is ∆H = -349 kJ mol

Why is the E.A. of Cl2 greater than that of F3

Ans : Fluorine has unexpectedly low electron affinity than chlorine. This is due to very small size of the fluorine atom. As aresult, there are strotuj intacelectcotuc repulsions irv the relatively small 2 euhehaii of electron does not feel much attraction. Therefore, its election affinity is less.

What is the order of oxidising capacity of halogens? Give an example to prove the order.

Ans : The decreasing order of oxidising capacity of halogens is Fluorine > Chlorine > Bromine > IodineFluorine displaces all other halogens from their ionic compounds.

Chlorine oxidises bromides and iodides to Br2 and I2 respectively.
Bromine oxidises iodides to I2.
Iodine cannot oxidise any ionic halide.

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