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

Element	Atomic Number	Electronic configuration	Atomic radius	Ionic radius	Electro-negativity	Electro-affinity	Atomic Mass
Fluorine [F]	9	[2,7] IS22S22P5	0.072	0.136	4.0	-3.35	19.0
Chlorine [Cl]	17	[2,8,7] IS22S2 2p63S23P5	-0.099	0.181	3.0	-3.61	35.5
Bromine [Br]	35	(2,8,18,7) ..3S23P63d104S2	-0.114	0.195	2.8	-3.36	80.0
Iodine [I]	53	(2,8,18,18,7) ….4S24P64d10	0.133	0.216	2.5	-3.06	126.9
Astatine [At]	85	(2,8,18,32,18,7) ..5S25P65d106S26P5	—-	—-	2.2	—-	210

PHYSICAL PROPERTIES OF THE HALOGENS

Element	Fluorine[F]	Chlorine[Cl]	Bromine [Br]	Iodine[I]
Atomic number	9	17	35	53
Relative Atomic Mass	19	25.5	79.9	126.9
Physical state at 20	Gas	Gas	Liquid	Solid
Colour	Pale yellow	Greenish yellow	Dark-red	Black
Density(g/cm3)	——	1.9	3.2	4.9
Melting point (). Boiling point (	-220	-101	-7	113
Solubility in water(g per 100g of water)	Reacts readily with water	0.59	3.6	0.018

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) + F_2(g) 2NaF_(s)

1. Halogens react with non-metals as shown below

C_(s) + 2F_2(g) CF_4(s)

Xe+ 2F XeF_4(s)

P_4(s) + 6I_2(s) 4PI_3(s)

P_4(s) + 6Cl_2(g) 4PCl_2(s)

P_4(s) + 10Cl_2(g) 4PCl_5(s)

H_2(g) + F_2(g) 2HF_(g)

H_2(g) + Cl_2(g) 2HC_l(g)

Br_2(g) + H_2(g) 2HBr_(g)

I_2(g) + H_2(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) + Cl_2(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.

2F_2(g) + 2H₂O_(l) 4HF_(g) + O₂

3F_2(g) + 3H₂O 6HF_(g) + O_3(g)

Cl_2(g) + H₂O_(l) HCl_(aq) + HClO_(aq)

1. Reaction with Alkalis

Cl_2(g) + 2NaOH_(aq) NaOCl_(aq) + NaCl + H₂O

3Cl_2(aq) + 6NaOH_(aq) NaClO_3(aq) + 5NaCl + 3H₂O_(l)

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

3Br_2(aq) + 6KOH_(aq) KBrO_3(aq)

3I_2(aq) + 6KOH_(aq) KIO_3(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 2^nd 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. 2^nd 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