HomeSS 2ELECTRONIC CONFIGURATION OF HALOGENS

ELECTRONIC CONFIGURATION OF HALOGENS

 

SECOND TERM E-LEARNING NOTES

SUBJECT: CHEMISTRY

CLASS: SS 2

SCHEME OF WORK

 

 

 

 

 

WEEK 4

TOPIC: HALOGENS

CONTENT:

  1. ELECTRONIC CONFIGURATION OF HALOGENS, PHYSICAL PROPERTIES OF HALOGENS AND GRADATION DOWN THE GROUP.
  2. CHEMICAL PROPERTIES OF HALOGENS AND GRADATION DOWN THE GROUP
  3. USES OF HALOGENS AND THEIR COMPOUNDS.

PERIOD 1 AND 2: ELECTRONIC CONFIGURATION OF HALOGENS

Halogens are found in group (viii) of the periodic table and consist of fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I) and Astatine (At),.

The name halogen is of Greek origin meaning salt formers because they readily form salts from metals. Halogens are very reactive non- metals with remarkable similarities in properties. This is because each halogen atom has seven only one electron to attain the octet. They are strong oxidizing agents with varying oxidation Numbers. The halogens are highly electro negative elements. The halogens share electrons to form covalent compounds or accept electrons to form ionic compounds. It is the electronic configuration of halogens that accounts for their electronegative nature, oxidising ability and the fact that they form mainly single covalent bonds.

ELECTRO CONFIGURATION AND SOME PROPERTIES OF THE HALOGENS AND GRADATION OF THE PROPERTIES

ElementAtomic

Number

Electronic configurationAtomic radiusIonic radiusElectro-negativityElectro-affinityAtomic

Mass

Fluorine [F]9[2,7] IS22S22P50.0720.1364.0-3.3519.0
Chlorine [Cl]17[2,8,7] IS22S2 2p63S23P5-0.0990.1813.0-3.6135.5
Bromine [Br]35(2,8,18,7)

..3S23P63d104S2

-0.1140.1952.8-3.3680.0
Iodine

[I]

53(2,8,18,18,7)

….4S24P64d10

0.1330.2162.5-3.06126.9
Astatine

[At]

85(2,8,18,32,18,7) ..5S25P65d106S26P5—-—-2.2—-210

PHYSICAL PROPERTIES OF THE HALOGENS

ElementFluorine[F]Chlorine[Cl]Bromine [Br]Iodine[I]
Atomic number9173553
Relative Atomic Mass1925.579.9126.9
Physical state at 20GasGasLiquidSolid
ColourPale yellowGreenish yellowDark-redBlack
Density(g/cm3)——1.93.24.9
Melting point (). Boiling point (-220-101-7113
Solubility in water(g per 100g of water)Reacts readily with water0.593.60.018

EVALUATION

  1. What is the atomic number of chlorine?
  2. With the knowledge of atomic number, draw the electronic configuration of chlorine.
  3. What is the colour of chlorine gas?

PERIOD 3: CHEMICAL PROPERTIES AND GRADATION DOWN THE GROUP

The chemical reactivity of the halogens decreases down the group from fluorine to iodine. The halogens are good oxidising agents and their oxidising power decreases from fluorine to iodine. The halogens try to attain the stable noble gas configuration either by sharing electrons or by accepting electrons. The following reactions illustrate the reactivity trend among the halogens.

  1. Halogens can react with metals as shown in the equations below

2Na(s) + F2(g) 2NaF(s)

  1. Halogens react with non-metals as shown below

C(s) + 2F2(g) CF4(s)

Xe+ 2F XeF4(s)

P4(s) + 6I2(s) 4PI3(s)

P4(s) + 6Cl2(g) 4PCl2(s)

P4(s) + 10Cl2(g) 4PCl5(s)

H2(g) + F2(g) 2HF(g)

H2(g) + Cl2(g) 2HCl(g)

Br2(g) + H2(g) 2HBr(g)

I2(g) + H2(g) 2HI(g)

The order of reacting is F2> Cl2>Br2>I2. The acid strength of the hydrogen halides follow the order:

HI>HBr>HCl>HF

The stability of Hydrogen halides decreases from chlorine to iodine: HCl>HBr>HI.

Chlorine is now an electron acceptor and so are other halogens and in so doing acts as oxidising agents.

2Na(s) + Cl2(g) 2Na+Cl–(s)

The order of decreasing power as oxidising agents is F2> Cl2>Br2>I2.

  1. More reactive halogen displaces the less reactive from aqueous solution

Cl2 + 2Br– 2Cl- + Br2

Cl2 + 2I– 2Cl– + I2

Br2 + 2I– 2Br– + I2

Iodine is a weak oxidizing agent.

  1. Reaction with water.

2F2(g) + 2H2O(l) 4HF(g) + O2

3F2(g) + 3H2O 6HF(g) + O3(g)

Cl2(g) + H2O(l) HCl(aq) + HClO(aq)

  1. Reaction with Alkalis

Cl2(g) + 2NaOH(aq) NaOCl(aq) + NaCl + H2O

3Cl2(aq) + 6NaOH(aq) NaClO3(aq) + 5NaCl + 3H2O(l)

Bromine and iodine react in a similar manner to form the oxobromate(v) and iodated(v) ions.

3Br2(aq) + 6KOH(aq) KBrO3(aq)

3I2(aq) + 6KOH(aq) KIO3(aq) +5KI(aq) + 3H2O(l)

EVALUATION

  1. Give one for each equation of reaction to demonstrate the reaction of Cl2, Br2, I2 and F2 respectively.

PERIOD 4: USES OF HALOGENS AND THEIR COMPOUNDS

  1. Fluorine is used in rocket propulsion and in making Uranium(iv) fluoride. It is also used in making fluorocarbon compounds which are used as refrigerant, aerosol propellant, anaesthetics and fire extinguisher and fluids. The flouoro- carbons contain only carbon and fluorine and are extremely inert and also are used as polytetrafluoroethene[PTFE] with the trade name Teflon in making valves, seals, gaskets, electrical insulators among others.
  2. CHLORINE: is used as oxidant in the manufacture of bromine and as bleach and germicide in treatment of water. Chlorine is used in production of HCl (hydrogen chloride) in commercial quantity, in the production of fabrics and papers and also insecticides. (e.g DDT)(3) Iodine dissolved in alcohol or potassium iodide [KI] is used as antiseptic for cuts and scratches.
  3. HYDROCHLORIC ACID which is one of the most laboratory acid, is used to remove rust from steel sheet before galvanizing.
  4. SODIUM OXOCHLORATE (I) [NaCLO] is used as disinfectant and for bleaching in laundries.
  5. SODIUM OXOCHLORATE (1) decomposes on warming to sodium oxochlorate(v), NaCLO3 which is used as weed killer.
  6. Tetrachloromethan and trichloroethene are degreasing solvents.
  7. Polychloroethene is used in making plastics
  8. Dettol is used as disinfectant and antiseptics.
  9. Dichlorodiphenyltrichloroethane (DDT) and benezehexachloride are used as pesticides
  10. Bromine finds application in the manufacture of dyestuffs and in making silver bromide used in photographic materials.

EVALUATION

Enumerate five uses of halogens you know[mediator_tech]

GENERAL EVALUATION

OBJECTIVE TEST:

  1. What is the atomic number of chlorine? A. 35 B. 53 C. 82 D. 17
  2. 2, 8,18,7 is the electronic configuration of A. F B. Cl C. Br D. I
  3. Why is the preparation of halogens carried out in a fume cupboard? A. they are odourless B. they are poisonous C. They are colourless D. They are harmless.
  4. In halogens the order of decreasing power as oxidising agents is

A. F2>Cl2>Br2>I2 B .Cl2>F2>Br2>I2 C. Br2>F2>I2>Cl2 D. Br2>Cl2>F2>I2

  1. In halogens, melting points and boiling points increase with an increase in A. Molecular mass B. Valence C. oxidation number D. Atomic number

ESSAY QUESTIONS

  1. Name two natural compounds of halogens.
  2. State the similarities in chemical properties of halogens giving balanced reactions.
  3. Write on the following giving balanced reaction examples. Halogen reaction with

(i) water (ii) iron (iii) alkali

  1. (a) What is the atomic number of chlorine? (b) Why is the preparation of halogens carried out in a fumed cupboard?
  2. What are the chemical properties of halogens?

WEEKEND ASSIGNMENT

  1. Read 2nd edition comprehensive certificate chemistry by by G.N.C Ohia, et al, pages 272-284

PRE READING ASSIGNMENT

Read about the uses of halogens and laboratory and chemical preparation of chlorine

WEEKEND ACTIVITY

  1. Write the formulae of the following.

(i) Chloroform (ii) iodoform (iii) Carbon tetrachloride (iv) fluorine molecule

  1. What are the uses of Carbon tetrachloride?

REFERENCES

  1. 2nd Edition Comprehensive Certificate Chemistry By By G.N.C Ohia, et al.
  2. New school chemistry for senior secondary schools by Osai Yaw Ababio reversed by L.E.S Akpanisi Herbert Igwe

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