The document discusses the halogens, which are the elements in group 17 of the periodic table (fluorine, chlorine, bromine, iodine, astatine). It provides details about their general properties, including their electron configuration, existence as diatomic molecules, colors, reactivity, and ability to gain electrons to achieve stable electronic structures. It also describes their physical and chemical properties such as ionization energy, electronegativity, electron affinity, and oxidizing power (which decreases down the group). Peculiar properties of fluorine are highlighted. Uses of halogens and facts about their presence in humans are also mentioned. Interhalogen compounds and pseudohalides/pseudohalogens

1. Group 17
The Halogens:
Fascinating aspects
1

2. fluorine
chlorine
bromine
iodine
I
Br
Cl
F
At
The elements in group 17 of the periodic
table, on the right, are called the
HALOGENS.
astatine
2

3. Why the name ….. HALOGEN??
* Halogen-metal compounds are salts
occurring in sea water
(e.g. NaCl; sodium chloride),
* halos = sea salts; genes=born.
3

4. STATE OF HALOGENS
• Astatine is radioactive and is one of the
rarest of the chemical elements.
4

5. Halogen Greek name meaning
Fluorine fluere Flow
(Fluorite melts when heated)
Chlorine chloros Greenish yellow
Bromine bromos Stench
Iodine iodes Violet
Astatine astatos Unstable (decay product of U, Th)
5

6.  poisonous and smelly.
 They are all toxic or harmful because they are
so reactive
GENERAL PROPERTIES OF THE HALOGENS
 Have 7 e- in their outer shells
 Exists as separate diatomic molecules ... F2, Cl2, Br2
 Colored and color darkens as we go down through the group
 non-metals
 do not conduct electricity
 never found free in nature because of their reactivity
– they are found as compounds with metals (eg. NaCl).
6

7. Electron configuration of halogens
Fluorine 1s2 2s2 2p5
Chlorine [Ne]3s2 3p5
Bromine [Ar]3d10 4s2 4p5
Iodine [Kr]4d10 5s2 5p5
Astatine [Xe]4f14 5d10 6s2 6p5
7

8. All halogens have seven electrons in their outer shell but one e- short of
the nearest noble gas configuration.
Electronic structure of halogens......
fluorine
2,7 (9)
chlorine
2,8,7 (17)
bromine
2,8,8,7 (35)
 They can easily attain a full and complete
outer shell by gaining one electron.
 They all gain an electron in reactions to
form negative ions with a -1 charge.
 So, they have similar chemical properties.
 Fluorine is the most electronegative
element in the periodic table and it has
no d orbitals in its valence shell, so it can't
expand its valence shell.
 Cl2, Br2 and I2 have valence shell d orbitals
and can expand their valence shells to hold
as many as 14 valence electrons.
8

9. All halogen atoms require one more electron to
obtain a full outer shell to become STABLE (8e-).
How do halogen molecules exist?
Each atom can achieve this by sharing one electron
with another atom to form a single covalent bond.
+ F F F F
So all halogens exist as diatomic molecules:
F2, Cl2, Br2 and I2. 9

10. 10

11. Physical properties of halogens
• Ionization energy
• Electron affinity
• Electronegativity
• Oxidizing states
• Oxidizing power
• Metals are electropositive (eg. Na)
• Non-metals are electronegative (Cl2)
11

12. Ionization Energy (decreases down the group)
Ionization energy (IE) is defined as the amount of
energy required to remove the most loosely valence
electron, of an isolated gaseous atom to form a cation.
If the outer valence electrons are far away from the
nucleus, it does not take as much energy to remove
them. So the energy required to pull off the
outermost electron will be less for the elements at the
bottom of the group since there are more energy
levels. Iodine lose an e- and forms I+
Also, the high ionization energy makes the element
appear non-metallic. Iodine and astatine display
metallic properties 12

13. Electronegativity (decreases down the group)
Electronegativity is a measure of the tendency of an atom
to attract a bonding pair of electrons towards itself.
The valence electrons will be at a distance from the
nucleus as we go down the group and therefore, the
nucleus and the electrons are not that much attracted
to each other. An increase in shielding is observed.
Electronegativity therefore decreases down the group.
So electrons can be easily removed from iodine.
13

14. Electron Affinity (decreases down the group)
Electron affinity of an atom or molecule is the amount of
energy released or spent when an electron is added to a
neutral atom or molecule in the gaseous state to form a
negative ion i.e X-
Since the atomic size increases down the group, electron
affinity generally decreases but only gradually
(At < I < Br < F < Cl)
However, fluorine has a lower electron affinity than
chlorine and this can be explained by the small size of
fluorine, compared to chlorine.
14

15. Oxidizing states of halogens
Halogen
Oxidation States in
Compounds
Fluorine (always) -1
Chlorine -1, +1, +3, +5, +7
Bromine -1, +1, +3, +4, +5
Iodine -1, +1, +5, +7
Astatine -1, +1, +3, +5, +7
-1 NaCl, +1 HClO, +3 BrF3, +5 HClO3 , +7 IF7
15

16. Oxidizing Power
(decreases down the halogen group)
• The halogens are strong oxidizing agents.
• The oxidizing power decreases from fluorine to
Iodine. Fluorine is the strongest oxidizing agent.
• It oxidizes other halide ions to halogens in
solution or when dry.
F2 + 2X-  2F- + X2; X- = Cl- , Br- , I-
(F2 has high e- affinity)
• Halogen of low atomic number oxidizes the
halide ion of higher atomic number.
16

17. 17

18. Oxidation or reduction?
18

19. How does electron structure affect reactivity?
Reactivity of alkali metals decreases going down the group
 The atoms of each element get larger
going down the group.
 This means that the outer shell gets
further away from the nucleus and is
shielded by more electron shells.
 The farther the outer shell is from the
positive attraction of the nucleus, the
harder it is to attract another electron
to complete the outer shell.
 This is why the reactivity of the halogens
decreases going down group 17.
decreaseinreactivity
F
Cl
Br
Reactivity: F > Cl > Br > I 19

20. Difficulties encountered in the
isolation of fluorine
• Fluorine is so reactive that it attacks the materials of all
the vessels. For example, fluorine attacks carbon and
silicon present in the glass vessels forming CF4 and SiF4
respectively.
• It also attacks the electrodes and vessels made of Pt to
form PtF4. Lead, iron and tin vessels were also found to
be unsuitable for the preparation.
• Isolation of fluorine from HF got failed because HF is so
stable that it cannot be decomposed by oxidizing
agents. 20

21. KHF2 KF +HF HF H + F
2H + 2e H2 (At cathode) 2F 2e F2 (At Anode)
Isolation of Fluorine: Dennis’ Method:
Fluorine is prepared by the electrolysis of fused potassium
hydrogen fluoride.
Electrolysis is carried out between graphite electrodes in a V-
shaped electrically heated copper tube. The ends of the tube are
covered with copper caps into which the graphite electrodes are
fixed with Bakelite cement. The copper tube is thickly bagged to
prevent loss of heat.
21

22. Fluorine liberated at the anode is passed through the U-tube containing
sodium fluoride. This removes the hydrogen fluoride vapors
coming with fluorine.
NaF +HF NaHF2
22

23. Abnormal behavior of fluorine
Fluorine differs from the other members
of the halogen family. This is due to
i) Small size
ii) High electronegativity
iii)Non availability of d orbitals in fluorine
23

24. Peculiarity of fluorine
Oxidation state : Halogens exhibit oxidation states of -
1,0,+1,+3,+5 and +7 where as fluorine exhibits only -1
oxidation state
Reactivity: Fluorine is the most reactive element among the
halogens. This is due to strong electrostatic repulsion
between the non bonding electrons present in fluorine
molecule. The F- F bond is very weak.
Behavior of hydrogen fluoride: Hydrogen fluoride has
abnormally high melting and boiling points than the other
hydrogen halides due to hydrogen bonding.
Formation of HF2
- ions : Due to hydrogen bonding the
fluoride ion forms the anion HF2
-. On the other hand
halides do not form such ions. E.g., KHF2
H F H F H F
24

25. Peculiarity of fluorine ….. continued
• Maximum covalency: As fluorine lacks d orbitals it
cannot have covalency more than one. But the other
halogens can have covalency up to 7. (eg. IF7)
• Formation of SF6: Due to small size and high
electronegativity, fluorine brings about the + 6 state in
sulphur forming SF6. Other halogens do not form such
hexahalides
• Complex formation: Flouride ion a greater tendency to
form [FeF6]3-, [AlF6]3-
• Formation of polyhalides: Due to the non-availability
of d-orbitals fluorine does not form any polyhalides. But
other halogens form polyhalide ions. E.g. [Br2]+, [I2]+ ,
[Cl3]+, [Br3]+, [I3]+ [I3]−
, [Br4]2−, [I4]2−etc 25

26. Electropositive nature of iodine
• It has the lowest electronegativity value , i.e.
highly electropositive. It behaves like a metal
• Like the other halogens, it has one electron short of
a full octet and reacts with many elements in order
to complete its outer shell, although in keeping
with periodic trends, it is the weakest oxidizing
agent among the stable halogens
• Similarly, the iodide anion, I−, is the strongest
reducing agent among the stable halogens, being
the most easily oxidized back to diatomic I2.
26

27. Basic Iodine
Metallic or basic properties increase down the group
Among the halogens, iodine shows strong basic
character.
For e.g. Iodine has a metallic lustre
has a tendency to form unipositive I+ ion
and tripositive I3
+ ion.
27
Atomic size increases from fluorine to iodine.
Thus the nucleus of I2 holds the electrons in the
orbit less firmly. So Iodine looses one e- easily
forming unipositive cation. I2  2I+ + 2e-

28. Evidence for basic iodine
ICl acts as a strong electrophilic iodinating
agent. This again confirms the basic character
of iodine.
28
OH
COOH
+ 2ICl
COOH
II
OH
+ 2HCl
Salicylic acid
3, 5- di-iodo
salicyclic acid

29. IODINE TEST …. A TEST FOR STARCH
Starch gives an intense "blue-black" color upon addition
of aqueous solutions of the triiodide anion (I3
-), due to
the formation of an intermolecular charge-transfer
complex. In the absence of starch, the brown color of the
aqueous solution remains. This interaction between starch
and triiodide is the basis for iodometry.
29
KI + I2  I3
-

30. Uses of halogens
Halogen Uses
Fluorine In tooth pastes, Teflon®
Chlorine purify water in wells, swimming pools etc as it
kills bacteria (chlorination)
Bromine Fire extinguishers, disinfectant, camera films
Iodine Iodized salt, in artificial rain, dyes, specialized soaps,
lubricants, photographic film, tincture, and
pharmaceuticals, test for starch, treatment of thyroid
disorders
30

31. Facts about halogens in human …
• There are 3 to 6 grams of fluorine,
• 95 grams of chlorine,
• 260 milligrams of bromine,
• 10 to 20 milligrams of iodine in a 70 kg person.
• Chlorine is found in human blood in a
concentration of 0.3%.
31

32. Interhalogen Compounds….
32

33. Interhalogen Compounds
• These covalent compounds are formed when two
different halogens react .
• These are formed due to the electronegativity difference
among the halogens.
Classification:
• Interhalogens have the general formula Axn where n=1, 3,
5 &7.
Type AX eg: ClF, BrF, BrCl, ICl, Ibr
Type AX3: eg : ClF3, BrF3, ICl3
Type AX5 eg: BrF5 ClF5 Type AX7 eg: IF7
When representing the compound, the less electro
negativity element has to be written first. 33

34. Iodine mono chloride ….. ICl
is formed by passing chlorine over
solid iodine at temperature below 0 0C.
I2 +Cl2 2ICl
• It is a red-brown chemical compound
• melts near room temperature.
• Because of the difference in the electronegativity
of iodine and chlorine, ICl is highly polar ; I+Cl-
* In organic synthesis, estimation of iodine No. of
oils and as a source of I+.
34

35. Bromine trifluoride… BrF3
• It is obtained by mixing bromine vapor and
fluorine in a stream of nitrogen at 20oC.
Br2 +3F2 2BrF3
It is a straw-colored liquid with a pungent odor.
It is a powerful fluorinating agent
It is used to produce uranium hexafluoride (UF6) in the
processing and reprocessing of nuclear fuel.
35

36. Bromo pentafluoride … BrF5
It is pale yellow liquid
By the direct reaction of bromine with
excess fluorine at temp. over 150°C
Br2 + 5 F2 → 2 BrF5
It is an extremely effective fluorinating agent, converting
most uranium compounds to the hexafluoride at room
temperature like BrF3 .
36

37. Iodine heptafluoride….IF7
• It is a colorless gas
• It is prepared by passing a mixture of iodine
pentafluoride vapors and fluorine through a
platinum tube at 300 0C.
• It is a strong oxidizing agent
• Used to prepare periodic acid.
IF5 +F2 IF7
37

38. Shapes of interhalogens
38

39. Pseudohalides
and
Pseudohalogens …
39

40. Pseudohalides & Pseudohalogens
Pseudohalides are univalent negative inorganic
radicals, composed of two or more electronegative
atoms (ions), which exhibit reactions similar to
those of the halide ions (X-).
E.g. Cyanide CN-
, Thiocyanide SCN- , Azide N3
-
Covalent dimers of such pseudohalides are called
pseudohalogens These possess properties similar to
those of halogens. Examples.,
–Cyanogens (CN)2 -Thiocyanogen(SCN)2
Selenocyanogen (SeCN)2 etc. 40

41. Similarities between pseudohalogens and halogens
1. Dimeric and isomorphic nature:
Cl2 is isomorphous to (CN)2; Br2 is isomorphous to (SCN)2.
2. Like halogens, pseudohalogens combine with metals like
silver, lead &mercury to form insoluble salts.
AgCN, Pb(CNS)2 (CN, CNS are pseudohalogens)
Ag+ + Cl-  AgCl; Ag+ + CN-  AgCN
3. Pseudohalogens also react with alkalis
Cl2 + 2OH-  Cl- + OCl- + H2O;
(SCN)2 + 2OH-  SCN- + OSCN- + H2O
41

42. Similarities … continued
4. Formation of monobasic hydracids:
Cl2 + H2  2HCl; (CN)2 + H2  2HCN
5. Addition to ethylenic bonds: Like halogens,
pseudohalogens also form addition
compounds with unsaturated hydrocarbons.
42

43. Preparation and properties of
pseudohalogens …
43

44. Preparation of cyanogen (CN)2
• Dry cyanogen is obtained by heating a mixture of
mercuric cyanide and mercuric chloride
2Hg(CN)2 Hg2(CN)2 + (CN)2
• It is a colorless, toxic gas with a pungent odor.
• The two cyano groups are bonded together at
their carbon atoms: N≡C−C≡N
• Uses: an important intermediate in the production of
many fertilizers. It is also used as a stabilizer in the
production of nitrocellulose.
44

45. Preparation of Thiocyanogen (SCN)2
• Adding lead thiocyanate to Br2 in methylene
chloride solution at 0oC.
Pb(SCN)2 + Br2  PbBr2 + (SCN)2
• PbBr2 (solid) is filtered off under argon gas
and the filtrate on evaporation yields free
thiocyangen.
45

46. Compd Uses
Na3AlF6 Manufacture of aluminum
BF3 Catalyst
CaF2 Optical components, manufacture of HF, metallurgical flux
ClF3 Fluorinating agent, reprocessing nuclear fuels
HF Manufacture of F2, AlF3, Na3AlF6, and fluorocarbons
LiF Ceramics manufacture, welding, and soldering
NaF Fluoridating water, dental prophylaxis, insecticide
SF6 Insulating gas for high-voltage electrical equipment
SnF2 Manufacture of toothpaste
UF6 Manufacture of uranium fuel for nuclear reactors
46

47. 47

48. DISPLACEMENT REACTIONS OF HALOGENS
Reactive halogen displaces less reactive one
from its salt solution…
Cl2 + 2NaBr  2NaCl + Br2
48

49. SUMMARY OF GROUP I7
49