Main group VII

1. Main group VII The Halogens Chapter 20

2. The Halogens • F,Cl,Br,I,At • All elements through the periodic table of elements do form halides • Exception: He,Ne,Ar • They are easiest to prepare • Use: precursors in synthesis reactions • Halides with elements with more than one valence are best known • In organic compounds the F have special properties

3. The Halides At is a greek name and means unstable. At has no stable isotope. At behaves like I, but is less electronegative.

4. The Halides • F: occurs widely as Fluorspar (CaF2) • Na3AlF6 Cryolite, • Ca3(PO4)2Ca(F,Cl)2 Fluorapatite. • It is more abundant than Chlorinne • F is obtained by electrolysis of molten fluorides. • Most common used electrolyte KF.2-3HF • Under electrolysis the melting point increases but the electrolyte is regenerated by HF

5. The Halides • Fluorine cells are made out of Steel, Cu, Ni-Cu alloys. • They become coated with a layer of fluoride. • Cathodes are steel or Cu. • Anodes ungraphitized carbon. • F2 is handled in metal apparatus • But it can be handled in glas, but HF needs to be removed by passing through anhydrous NaF,KF forming MHF2

6. The Halides Fluorine is the most chemically reactive of all the elements combines directly (often with extreme vigor), at ordinary or elevated temperatures, with all the elements other than 02, He, Ne, and Kr. Attacks many compounds transforming them to fluorides. Organic material burn in F2.

7. The Halides The great reactivity ofF2 is in part attributable to the low dissociation energy of the F-F bond, and because reactions of atomic fluorine are strongly exothermic. The low F-F bond energy is probably due to repulsion between nonbonding electrons

8. The Halides Chlorine occurs as NaCl, KCI, MgCl2sea water, salt lakes deposits originating from the prehistoric evaporation of salt lakes. Cl2 is obtained by electrolysis of brine. Old technology: Mercury cathode New technology: Membrane cells

9. The Halides Chlorine is a greenish gas It is moderately soluble in water Bromine occurs in much smaller amounts, as bromides, along with chlorides

10. The Halides Bromine is a dense, mobile, dark red liquid at room temperature It is moderately soluble in water and miscible with nonpolar solvents such as CS2and CCI4 Iodine occurs as iodide in brines and as iodate in Chile saltpeter NaNO3 Various forms of marine life concentrate iodine

11. The Halides Production of 12 involves either oxidizing 1-or reducing iodates to 1-followed by oxidation An acid solution of Mn02is commonly used as the oxidant. Iodine is a black solid with a slight metallic luster I2 sublimes at 1atm without melting

12. The Halides Soluble in nonpolar solvents such as CS2 and CCI4 Colour: Purple In polar solvents, unsaturated hydro carbons, and liquid S02' brown or pinkish-brown solutions are formed. colors indicate the formation of weak complexes I2 ---S known as charge-transfer complexes.

13. The Halides The bonding energy results from partial transfer of charge in the sense I2-S+ I2,Br2,Cl2 and Icl can sometimes be isolated as crystalline solids at low temperatures Iodine forms a blue complex with starch, in which the iodine forms linear I5- ions in channels in the polysaccharide amylose

14. The Halides At has been found as a product of the U and Th decay series. About 20 isotopes of At are known The longest lived has a half-life of 8.3 h At seems to follow the trend of the other halogens. It is volatile, somewhat soluble in water

15. The Halides There are many types of halides. Binary Haliddes Form simple molecules, complex infinite arrays. Metal halides in +1,+2,+3 oxidation state are ionic. Many metals show their highest oxidation state in fluorides

16. The Halides • Preparation of Anhydrous Halides • 1. Direct interaction with the elements • Direct fluorination normally gives fluorides in the higher oxidation states • Most metals and nonmetals react very vigorously with F2 • nonmetals such as P4 the reaction may be explosive • Metal and halide react faster in THF. The Halide is a solvate.

17. The Halides • 2. Dehydration of hydrated halides • The dissolution of metals, oxides, or carbonates in aqueous halogen acids followed by evaporation or crystallization gives hydrated halides. • Dehydration of chlorides can be effected by thionyl chloride

18. The Halides • 3. Treatment of oxides with other halogen compounds • Oxides may often be treated with halogen-containing compounds to replace oxygen with halogen

19. The Halides • 4. Halogen exchange • Many halides react to exchange halogen with • (a) elemental halogens • (b) acid halides • (c) halide salts • (d) an excess of another halogen con-taining substance • Chlorides can often be converted to either bromides (by KBr) or especially to iodides (by KI)

20. The Halides Halogen exchange is especially important for the synthesis of fluorides from chlorides, using various metal fluorides such as CoF3or AsF5.

21. The Halides Molecular Halides Molecular Halides are also called covalent halides. Between 2 metal atoms, most common 2 halogen atoms.

22. The Halides A fairly general property of molecular halides is their easy hydrolysis, for example

23. The Halides Reaction of Halogens with H2O and OH- The halogens are all soluble in water to some extent. In such solutions there are species other than solvated halogen molecules disproportionation reaction occurs rapidly.

24. The Halides

25. The Noble gases • Occurrence: • Minor constituents of the atmosphere • He : radioactive minerals, natural gas • Origin fromt he decay of U, Th that emit alpha particles. • The alpha particles are He nuclei athat acquire electrons from surounding medium. • He stays trapped in the rocks. • Rn is radioactive, comes formt he decay series of U, Th

26. The Noble Gases Properties of the Noble Gases:

27. The Noble Gases Ne,Ar,Kr,Xe prepared by fractionation of liquid air. Known as inert gases Thought not to have any reactivity Key to the problem of valency, the interpretation od the periodic table, and the concept of the closed electron shell configuration. Point of reference

28. The Noble Gases He: Main use cryoscopy. Ar: Used to provide an inert atmosphere Ne: Used in discharge lamps Rn: Health hazard in houses, Cancerogenicc

29. The Noble Gases Xe Chemistry

30. The Noble Gases Chemistry of Xe Fluorides: Thermodynamic studies show that only these 3 fluorides exist

31. The Noble Gases Chemistry of Xe: Xenon difluoride (XeF2) preparation by interaction of Xe with a deficiency of F2 at high pressures Soluble in water Hydrolysis is slow in acid solution, but rapid in the presence of bases

32. The Noble Gases Xenon tetrafluoride (XeF4 ) is the easiest of the three fluorides to prepare. On heating a 1:5 mixture of Xe and F2 at 400°C and about 6-atm pressure for a few hours, XeF4 is formed quantitatively. Fluorination agent in organic chemistry

33. The Noble Gases Xenon hexafluoride (XeF6 ) is obtained by the interaction ofXeF4 and F2 under pressure or directly from Xe and F2 at temperatures above 250°C and pressures greater than 50 atm. Xenon hexafluoride is extremely reactive, attacking even quartz

34. The Noble Gases Xenon hexafluoride is a strong acid according to the Lux-Flood definition It accepts oxide ion from other compounds and inserts fluoride ion in its place.

35. The Noble Gases • The xenon fluorides will react with strong Lewis acids such as SbFs or 1rFs • 3 types of adducts formed by XeF2 are: XeF2.MF5, • 2XeF2.MF5 • XeF2.2MF5 • where M = Ru, Ir, Pt, and so on. • molecular rather than ionic structure, in most cases adduct formation involves fluoride ion transfer to give structures that contain ions, such as XeF+

36. The Noble Gases Crystal structure of XeF

37. The Noble Gases Xenon hexafluoride can act as a Lewis acid toward F-and can be converted to heptafluoro or octafluoro xenates Most stable compounds, decompose above 400 degC.

38. The Noble Gases Xenon-Oxygen Compounds On evaporation of water, XeO3 is obtained as a white deliquescent solid that is dangerously explosive.