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Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET PDF Download

What are Halogens?

The halogens are the elements that form group 17 of the periodic table. They are reactive nonmetals and include fluorine, chlorine, bromine, and iodine.

Halogens are highly reactive non-metals. These elements greatly resemble in property with each other. Group 17 elements are collectively called halogens (In Greek: halo means salt and genes mean producing, so collectively salt-producing) and it consists of fluorine, chlorine, bromine, iodine, and astatine.

The 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 (ns2np5) and are short of one electron from the configuration of the nearest noble gas. The chemical properties and reactivity of an element are determined by the oxidation state exhibited by them.Group 17 - HalogensGroup 17 - Halogens


General Physical Properties of Group 17 Elements:

  1. Electronic configuration: 

    Their valence shell electronic configuration is nsnp5.
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  2. Physical state: 

    Intermolecular forces in halogens are weak and increase down the group. Thus, F2 and Cl2 are gases, Br2 is volatile liquid and I2 is solid.
  3. Atomicity: 

    All are diatomic in nature.
  4. Abundance: 

    Being very reactive in nature, they are not found free in nature. Their presence in the earth’s crust follows the order: F2 > Cl2 > Br2 > I2
  5. Colour: 

    They absorb light in the visible range forming excited states and are thus, coloured in nature.
    F2 ⇒ pale Yellow
    Cl2 ⇒ yellowish green
    Br2 ⇒ reddish brown
    I2 ⇒ deep violet
  6. Metallic character: 

    All the elements are non-metals and metallic character increases down the group. Thus, 1 forms 1+.
  7. Oxidation state:

    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET

  8. Bond energy & bond length: 

    The bond length increases from fluorine to iodine and in the same order bond energy decreases. However, the bond dissociation energy of F2 is lesser due to its smaller size. The order of bond energy is:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  9. Density: 

    It increases down the group in a regular fashion and follows the order F > Cl > Br >I.
  10. Ionisation enthalpy: 

    The ionisation enthalpy of halogens is very high and decreases down the group. The iodine also forms I+ and I3+ and forms compounds like LiI, lCN, IPO4. In a molten state, the compounds conduct electricity showing ionic character.
  11. Electron affinity: 

    The halogens have high values for electron affinity. The order of electron affinity is: Cl2 > F2 > Br2 > I2
    Due to the small size of fluorine (hence, high electron density), the extra electron to be added feels more electron-electron repulsion. Therefore, fluorine has less value for electron affinity than chlorine.
  12. Reduction potentials and oxidising nature: 

    red of halogens are positive and decrease from F to I. Therefore, halogens act as strong oxidising agents and their oxidising power decreases from fluorine to iodine. Fluorine is the strongest oxidising agent and is most reactive. That’s why it is prepared by the electrolysis of a mixture of KHF2 and anhydrous HF using Monel metal as a catalyst.
  13. Solubility: Halogens are soluble in water which follows the order: F2 > Cl2 > Br2 > I2
    The solubility of iodine in water is enhanced in the presence of KI.
    KI + I2 ⇔ KI3 ⇔ K+ + I2
    I2 forms a blue colour complex with starch.

Chemical Properties of Group 17 Elements:

  1. Hydrides: 

    HF is a low boiling liquid due to intermolecular hydrogen bonding, while HCI, HBr, HI are gases. The boiling point follows the trend: HF > Hi > HBr > HCl
    Some other properties show the following trend:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  2. Oxides: 

    Fluorine forms two oxides, OF2 and O2F2, but only OF2 is thermally stable at 298K. O2F2 oxidises Plutonium to PuF6 and the reaction is used for removing plutonium as PuF6 from spent nuclear fuel.
    Chlorine forms a number of oxides such as, CI2O, CI2O3, Cl2O5 , Cl2O7 , CIO2 and CIO2 is used as a bleaching agent for paper pulp, textiles and in water treatment.
    Br2O, BrO2, BrOare the least stable bromine oxides and exist only at low temperatures. They are very powerful oxidising agents.
    The iodine oxides, i.e., I2O4, I2O5, I2O7 are insoluble solids and decompose on heating. I2Ois a very good oxidising agent and is used in the estimation of carbon monoxide.
  3. Reaction with alkali:

    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEETOther halogens form hypohalite with dilute NaOH and hypohalite with conc. NaOH4.Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  4. Oxoacids of halogens: 

    Higher oxoacids of fluorine such as HFO2, HFO3 do not exist because fluorine is the most electronegative and has the absence of d-orbitals.
    +3 oxidation state of bromine and iodine are unstable due to the inert pair effect. Therefore, HBrO2 and HIO2 do not exist.
    Acidic character of oxoacids decreases as the electronegativity of the halogen atom decreases. Thus, the order of acidic strength.Group 17 Elements: Halogens Family | Chemistry Class 12 - NEETFor the oxoacids of the same halogens. acidic strength and thermal stability increase as the number of O atoms increases.

Interhalogen Compounds:

  • When two different halogens react with each other, interhalogen compounds are formed. These compounds are covalent and diamagnetic in nature. They are volatile solids or liquids except for elf which is a gas at 298 K. Interhalogen compounds are more reactive than halogens (except fluorine).
  • The XY3 type compounds have bent ‘T’ shape, XY5 type compounds have square pyramidal shape and IF7 has pentagonal bipyramidal structure.
  • BrF3 has “T” shaped structure due to 3 bp and 2 lp.
  • ICI is more reactive than I2 due to a weak bond. ClF3 and BrF3 are used for the production of UF6 in the enrichment of 235 U.
  • U(s) + 3CIF3(l) → UF6(g) + 3CIF(g)

Pseudohalogens and Pseudohalides:

The substances behaving like halogens are known as pseudohalides. Some examples are

Pseudohalogenn

Pseudohalide ion

(CM)2 Cyanogen

CN- Cyanide

(OCN)2 Oxycyanogen

OCN- Cyanate

 (SCN)2 Thiocyanogen       

SCN- Thiocyanate

 

Chlorine and its Compounds:

Occurrence:

Common salt, NaCl is most important. Chlorine is also present in sea water and as rock salt.

Preparation of Chlorine:

  1. By oxidation of conc. HCl:
    4NaCl + Mn02 + 4H2SO4 → 4NaHSO4 + MnCl2 + 2H2O + Cl2
  2. Weldon’s process
    MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
  3. Deacon’s process 
    In this process, HCl is oxidised by O2 in the presence of CuCl2 as a catalyst at 400oC.
    4HCl + O2 → 2Cl2 + 2H2O
  4. Electrolytic process:  By the electrolysis of brine solution in Nelson cell.Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET2Na+ 2e- → 2Na + H2O → 2NaOH + H2 (at cathode)
    2Cl- → 2Cl +  2e- → Cl2  (at anode)

Properties:

It is yellowish-green gas, collected by upward displacement of air poisonous in nature, soluble in water. Its aqueous solution is known as chlorine water.

Chemical Reactions:

  1. Action of water:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEETColoured matter + [0] → colourless matter. The bleaching action of chlorine is due to oxidation and is permanent.
  2. Action of hydrogen:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET  
  3. Displacement reactions:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  4. Action of NaOH (cold):
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEETAn aqueous solution of NaOCl is called Javelle water, 
  5. Action of H2S:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  6. Action of dry SO2:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  7. Action of CO:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  8. Oxidising properties:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  9. Reaction with ammonia:
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET
  10. Chromyl chloride test: When a mixture of chloride and solid K2Cr2O7 is heated with concentrated H2SO4 in a dry test tube, deep red vapours of chromyl chloride are evolved.
    Group 17 Elements: Halogens Family | Chemistry Class 12 - NEETWhen these vapours are passed through NaOH solution, the solution becomes yellow due to the formation of sodium chromate.Group 17 Elements: Halogens Family | Chemistry Class 12 - NEETThe yellow solution is neutralised with acetic acid and on the addition of lead acetate gives a yellow precipitate of lead chromate.Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET

Uses: 

It is used as a bleaching agent, disinfectant and in the manufacture of CHCl3, CCl4, DDT, anti-knocking compounds and bleaching powder.

2. Hydrochloric Acid (HCl)

Preparation: 

Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET

Properties:

It is a colourless and pungent-smelling gas. It is extremely soluble in water and ionises as below:
Group 17 Elements: Halogens Family | Chemistry Class 12 - NEET

[Noble metals like gold, platinum can dissolve in aqua-regia [three part conc. HCl and one part of conc. HNO3].

Uses:

It is used in the manufacture of chlorides. Chlorine, in textile and dyeing industries, in medicine and in the extraction of glue from animal tissues and bones.

Iodine (I2)

  1. Its major source is deep seaweeds of laminaria variety. Their ashes which are called kelp contain 0.5% iodine as iodides.
  2. Another source of I2 is caliche or crude chile saltpetre (NaNO3) which contains 0.2%, NaIO3. Iodine is purified by sublimation.
  3. It shows no reaction with water. The tincture of iodine is a mixture of I2 and KI dissolved in rectified spirit.
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FAQs on Group 17 Elements: Halogens Family - Chemistry Class 12 - NEET

1. What are halogens?
Ans. Halogens are a group of elements in the periodic table that belong to Group 17. These elements include fluorine, chlorine, bromine, iodine, and astatine. They are highly reactive nonmetals and are known for their strong oxidizing properties.
2. What are the general physical properties of Group 17 elements?
Ans. The general physical properties of Group 17 elements include being nonmetals, having relatively low melting and boiling points compared to other elements, and existing in various states of matter at room temperature (fluorine and chlorine are gases, bromine is a liquid, and iodine is a solid).
3. What are the chemical properties of Group 17 elements?
Ans. The chemical properties of Group 17 elements include their ability to readily gain an electron to achieve a stable electron configuration, forming negatively charged ions known as halides. They are strong oxidizing agents and can react with metals to form salts. They also readily form covalent compounds with other elements.
4. What are interhalogen compounds?
Ans. Interhalogen compounds are compounds formed by the combination of two different halogen elements. For example, chlorine and fluorine can combine to form chlorine trifluoride (ClF3). These compounds often exhibit unique properties and are used in various industrial applications.
5. What are inert gases?
Ans. Inert gases, also known as noble gases, are a group of elements in Group 18 of the periodic table. These elements include helium, neon, argon, krypton, xenon, and radon. They are characterized by their extremely low reactivity and stable electron configurations. Inert gases are often used in lighting, as fillers in incandescent bulbs, and in various other applications where their lack of reactivity is beneficial.
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