Halogens P-block elements

1. P-block Elements
VI A- GROUP 17

2.  Group 17 elements, fluorine (F), chlorine (Cl), bromine (Br),
iodine (I) and astatine (At), belong to halogen family.
 Electron configurations ns2np5 (n is the period number).
 In its elemental state, all halogens atoms combine to form
diatomic molecules (ex F2,I2,…)
 With the exception of F, the halogens can also lose valence
electrons and their oxidation states can range from -1 to +7
Group 17: The Halogens
The Halogen

3. Group 17: The Halogens
General trend
 Atomic and ionic radii:
 Halogens have the smallest atomic radii in their respective periods because of maximum effective
nuclear charge.
 Ionisation enthalpy:
 They have very high ionization enthalpy because of small size as compared to other groups.
 Electron gain enthalpy:
 Halogens have maximum negative electron gain enthalpy because these elements have only one
electron less than stable noble gas configuration.
 Electron gain enthalpy becomes less negative down the group because atomic size increases.
 Eelctronegativity:
 These elements are highly electronegative and electronegativity decreases down the group. They have
high effective nuclear charge.

4. Group 17: The Halogens
General trend
 Bond dissociation enthalpy:
 Bond dissociation enthalpy follows the order Cl2 > Br2 > F2 > I2
 This is because as the size increases bond length increases.
 Bond dissociation enthalpy of Cl2 is more than F2 because there are large electronic repulsions of lone
pairs present in F2.
 Colour:
 All halogens are coloured because of absorption of radiations in visible region which results in the
excitation of outer electrons to higher energy levels.
 Oxidising power:
 All halogens are strong oxidising agents because they have a strong tendency to accept electrons.
 Order of oxidizing power is F2 > Cl2 > Br2 > I2

5. Group 17: The Halogens
Gaseous Liquid Solid
Chlorine Bromine Iodine
• Because the atoms INCREASE in
atomic size down the group, the
electron clouds of these non polar
atoms become increasingly polarized,
which leads to weak van Der Waals
forces among the atoms.
• Thus, the formation of liquids and
solids is more possible for these
heavier elements because of their
melting and boiling points.

6. Group 17: The Halogens
General trend
 Trends in selected physical properties of the group 17 elements

7. Group 17: The Halogens
 All the halogens react directly with hydrogen, forming covalent bonds and (at sufficient levels of purity)
colorless gases at room temperature.
 Hydrogen reacts with fluorine, chlorine, bromine, and iodine, forming HF, HCl, HBr, and HI, respectively.
 The hydrogen halides (HX) can be prepared by the direct reaction of the elements.
H2(g) + X2 (g)  2HX(g)
 Fluorine reacts explosively by a radical chain reaction as soon as the F2 and H2 are mixed.
 The mixture of H2 and Cl2 explodes when it is exposed to light.
 Br2 and I2 react much more slowly.
 Another way to produce the hydrogen halides is the reaction of a metal halide with a non-volatile acid
CaF2 (s) + 2H2SO4 (aq, conc)  Ca(HSO4)2(aq) + 2HF(g).
 All hydrogen halides dissolve in water to give acidic solutions
Compounds of the Halogens (Hydrogen Halides)

8. Group 17: The Halogens
 The bond strength of these molecules decreases down the group: HF>HCl>HBr>HI.
 Acidic strength: HF < HCl < HBr < HI increases down the group
 Stability: HF > HCl > HBr > HI decreases down the group
 This is because of decrease in bond dissociation enthalpy.
 Boiling point: HCl < HBr < HI < HF increases down the group expect HF
 HF has strong intermolecular H bonding
 As the size increases van der Waals forces increases and hence boiling point increases
Reactivity with H2:
Compounds of the Halogens (Hydrogen Halides)

9. Group 17: The Halogens
 Halogens react with metals to form halides.
 Ionic character: MF > MCl > MBr > MI decreases down the group
 Halides in higher oxidation state will be more covalent than the one in the lower
oxidation state.
Reactivity with metals:

10. Group 17: The Halogens
 Fluorine forms only one oxoacid HOF (Fluoric (I) acid or
hypofluorous acid) due to high electronegativity.
 Acid strength: HOF > HOCl > HOBr > HOI
 This is because Fluorine is most electronegative.
 Acid strength: HOCl < HClO2 < HClO3 < HClO4
 Reason: HClO4 → H+ + ClO4-
 The acid strengths and the oxidizing ability of the
halogen oxoacids increase with the oxidation number of
the halogens
 most stable
Compounds of the Halogens (Oxoacids)

11. Group 17: The Halogens
 Hypohalous acids (HXO note +1 oxidation number) are prepared by direct reaction of the halogen with
water
 Cl2(g) + H2O(g)  HClO(g) + HCl
 Hypohalite ions (XO-) are formed when a halogen is added to the aqueous solution of a base
 Calcium hypochlorite (Ca(ClO)2) is used to chlorinate swimming pools
 because when placed in the pool it forms Ca2+ ions which form insoluble calcium carbonate which can
be removed through filter systems.
 Because hypochlorites (HClO) oxidize organic material they are used in liquid household bleaches and
as disinfectants.
Compounds of the Halogens (Oxoacids)

12. Group 17: The Halogens
 Binary compounds of two different halogen atoms of general formula X Xn are called interhalogen
compounds where n = 1, 3, 5, or 7
 These are covalent compounds.
 Interhalogen compounds are more reactive than halogens because X-X’ is a more polar bond than X-X
bond.
 All are diamagnetic.
 Their melting point is little higher than halogens.
 XX (CIF, BrF, BrCl, ICl, IBr, IF) (Linear shape)
 XX3 (CIF3, BrF3, IF3 , ICl3) (Bent T- shape)
 XX5 – CIF5, BrF5, IF5, (square pyramidal shape)
 XX7 – IF7 (Pentagonal bipyramidal shape)
Compounds of the Halogens(Interhalogen)
Reactivity of halogens towards other halogens:

13. Group 17: The Halogens
Compounds of the Halogens(Interhalogen)

14. Group 17: The Halogens
 These compounds are prepared by direct reaction of the
two halogens, the product formed being determined by the
proportions of the reactants used
Example:
Cl2(g) + 3F2 (g)  2ClF3(g)
Cl2 (g) + 5F2 (g)  2ClF5(g)
Compounds of the Halogens(Interhalogen)

15. Group 17: The Halogens
The Elements (Fluorine)
 Fluorine is the halogen with greatest abundance in the Earth’s crust. It occurs widely in many minerals
 Fluorine is the most strongly oxidizing element. Therefore, it cannot be obtained from its compounds by
oxidation with another element.
 Fluorine is produced by electrolyzing an anhydrous molten mixture of potassium fluoride and hydrogen
fluoride at about 75ºC with a carbon anode
 Most of the F produced by industry is used to make the volatile solid UF6 used for processing nuclear fuel.
 The next biggest user of F is the production of SF6 for electrical equipment.
 It is the most electronegative element.
 It has an oxidation number of -1 in all its compounds.
 The high electronegativity and small size (it allows for several F atoms to pack around a central atom) allow
it to oxide other elements to their highest oxidation number.
 F is less soluble than other halides.

16. Group 17: The Halogens
 Chlorine is more soluble in water than fluorine.
 As a result even though there is more F present in the Earth’s crust the oceans are salty with chlorides rather
than fluorides
 Cl is one of the most heavily manufactured chemicals.
 It is obtained from electrolysis of molten rock salt (NaCl) or brine.
 Cl will directly react with nearly all the elements except for C, N,O and the noble gases
 It is a strong oxidizing agent.
 It is gas.
 Uses:
 In a number of industrial processes, including the manufacture of plastics, solvents, and pesticides.
 It is also used as bleach in the paper and textile industries and as a disinfectant in water treatment plants.
 In addition, Cl is used to produce Br.
The Elements (Chlorine)

17. Group 17: The Halogens
The Elements (Bromine)
Uses:
Br is used widely in synthetic organic chemistry because of the ease at which it can be
added to and removed from organic chemicals.
Organic bromides are incorporated into textiles as fire retardants and are used as
pesticides.
Inorganic bromides, particularly silver bromide, are used in photographic emulsions
Properties:
• Corrosive
• Red-Brown
• Liquid
 Bromine is a reddish-brown fuming liquid at room temperature.
 It is the only non-metal that is a liquid at normal room conditions.
 Bromine on the skin causes painful burns that heal very slowly. It is an element to be treated with the
extreme respect in the laboratory.
 Elemental bromine is made by oxidation, removal of electrons from bromide ions in brine.

18. Group 17: The Halogens
 When iodine dissolves in organic solvents it produces solutions having a variety of colors.
 Iodine is an essential trace element for living systems; a deficiency in humans leads to a swelling of
the thyroid gland in the neck
 Iodides are added to table salt (iodized salt) to prevent this deficiency.
The Elements (Iodine)

19.  Astatine could be described as the most rare element on earth.
 All isotopes are radioactive; even its name is Greek for "unstable.
 At occurs naturally as one of the atoms produced when the 235U isotope undergoes radioactive decay.
 However, astatine does not stay around long. Most of its identified isotopes have half-lives of less than
one minute.
 Weighable amounts of astatine have never been isolated, and little is known about its chemical or
physical properties.
 In a mass spectrometer, astatine behaves much like the other halogens, especially iodine.
 There is evidence of compounds formed by its combining with other halogens, such as AtI, AtBr, and
AtCl.
The Elements (Astatine)