Chapter 17 Group 17 Elements. Physical Properties The elements Hydrogen Halides Interhalogen compounds and polyhalogen ions Oxoacids and salts

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1 Chapter 17 Group 17 Elements Physical Properties The elements Hydrogen Halides Interhalogen compounds and polyhalogen ions Oxoacids and salts 1

2 Bromine resources and commercial demand 2NaClO 3 + 2NaCl + 2H 2 SO 4 2ClO 2 + Cl 2 + 2Na 2 SO 4 + 2H 2 O 5NaClO 2 + 4HCl 4ClO 2 + 5NaCl + 2H 2 O 2

Fluorine has several differences in properties from later halogens:

) Small size Low dissociation energy for F 2, bond breaks easily.

87 V) High electronegativity (highest element) The A-F bond is

strengthens bonds Fluorocarbons are volatile, have weak London forces.

3 Fluorine has several differences in properties from later halogens: Only exists in -1 formal oxidation state (unlike HClO 4, HClO 3 etc.) Small size Low dissociation energy for F 2, bond breaks easily. High oxidation power (+2.87 V) High electronegativity (highest element) The A-F bond is stronger than A-Cl bond Small size and good overlap of atomic orbitals strengthens bonds Fluorocarbons are volatile, have weak London forces. Nonpolarizable F Small size also leads to large lattice energies in solids Born-Lande equation. (melting point: NaF 993 C; NaCl 801 C) 3

4 [I(py) 2 ] Although anions are the most commonly observed ion form a group 17 elements, cations can be stabilized by complexation or solvation. Fluorine-19 NMR 19 F is (spin I =1/2, 100%) is valuable in structure elucidation and investigating reaction mechanisms. Neutron Activation Analysis Naturally occurring 19 F is converted to 20 F by neutron bombardment, the radioactive decay is monitored, allowing the original amount of 19 F in the sample to be determined. Fluoride ion-selective electrode An electrode that is sensitive to the concentration of a specific ion is called an ion sensitive electrode. (a ph meter electrode is sensitive to H + ions.) 4

5 Difluorine Difluorine is a pale yellow gas, but is difficult to store since it is highly reactive and extremely corrosive. Glass can be used* if the gas is freed of HF NaF + HF NaHF 2 SiO 2 + 2F 2 SiF 4 + O 2 SiO 2 + 4HF SiF 4 + 2H 2 O *Reaction is slow unless SiO 2 is powdered 2H 2 O + 2F 2 4HF + O 2 Typical F 2 source is gas cylinders, but F 2 may be produced by decomposition: K 2 MnF 6 + 2SbF K 2KSbF 6 + MnF 2 + F 2 Diiodine, dibromine, and dichlorine Cl 2 may be purchased for laboratory use, but also may be prepared in the lab scale by: MnO 2 + 4HCl MnCl 2 + Cl 2 + 2H 2 O Layered solid Solid State Structures van der Waals radius, r v Cl 180 pm Br 195 pm I 215 pm 5

6 Charge transfer complexes A charge transfer complex is one in which a donor and acceptor interact weakly together with some transfer of electronic charge, usually facilitated by the acceptor. HOMO-LUMO gap decreases in the order F 2 > Cl 2 > Br 2 > I 2 Shift in the absorption maximum from the near UV to the red region of the visible spectrum. When combined with donor atoms (e.g. ethers, ketones, pyridine), Br 2 and I 2 form charge transfer complexes with the halogen s* MO acting as the acceptor orbital. Solutions of I 2 in donor solvents are typically brown or yellow. Electronic spectrum contains an intense absorption in the UV ( nm) region arising a charge transfer band. 2MeCN Br Example charge transfer complexes charge transfer complexes involving Br 2 - chain structure of C 6 H 6 Br2 1,2,4,5-(EtS) 4 C 6 H 2 (Br2 ) 2 Ph 3 P Br 2 6

7 . Proposed bonding scheme for [(AgI 2 ) n ] n illustrating the ability of I 2 to act as both a charge donor and a charge acceptor. Physical Properties of hydrogen halides 7

8 IBr -ICl ClF 8

9 Cation-anion interaction [I 2 F 12 ] 2- dimer [BrF 4 ] [Sb 2 F 11 ] - dimer 9

10 Bonding in [XY 2 ] - ions Review Chapter 5 MO theory Homonuclear cations are known: Polyhalogen Cations [Br 2 ] +, [I 2 ] +, [Cl 3 ] +, [Br 3 ] +, [I 3 ] +, [Br 5 ] +, [I 5 ] +, [I 4 ] 2+ Br 2 + SbF 5 --BrF 5 [Br 2 ] + [Sb 3 F 16 ] - (unbalanced) 2I 2 + S 2 O 6 F 2 ---HSO 3 F 2[I 2 ] + [SO 3 F] - Using MO theory, predict the change in X-X bond length on going from X 2 to [X 2 ] + [Br 2 ] + [Sb 3 F 16 ] - Br-Br stretching is 368 cm -1 Br 2 Br-Br stretching is 320 cm -1 I 2+ [I 2 ] + dimerizes at 193 K to give [I 4 ] 2+ I I 2I 2 + 3AsF 5 liq SO 2 [I 4 ][AsF 6 ] 2 + AsF 3 I 3Br 2 + 2[O 2 ] + [AsF 6 ] - 2[Br 3 ] + [AsF 6 ] - + 2O 2 3I 2 + 3AsF 5 liq SO 2 2[I 3 ] + [AsF 6 ] - + AsF 3 10

11 Polyhalide anions Homonuclear polyhalide anions are known: [I 3 ] -, [I 4 ] 2-, [I 5 ] -, [I 7 ] -, [I 8 ] 2-, [I 9 ] -, [I 10 ] 4-, [I 12 ] 2-, [I 16 ] 2-, [I 16 ] 4-, [I 22 ] 4-, [I 26 ] 3-, [I 29 ] 3- [I 5 ] - [I 7 ] - [I 8 ] - Oxides of chlorine, bromine, and iodine Iodine is the only halogen to form an oxide which is thermodynamically stable with respect to decomposition into its elements. I 2 + 5/2 O 2 I 2 O 5 D f H o (298 K) = kj mol -1 11

12 Br 2 O 3, 195 K Br 2 O 3 O 3, 195 K Br 2 O 5 Brown Orange Colorless Charge separated species for coordination numbers greater than 4 and still obey the octet rule. CCl 3 F, 195 K H 2 O + 2BrOTeF 5 Br 2 O + 2HOTeF 5 2Cl 2 + 3HgO Cl 2 O + Hg 3 O 2 Cl 2 2Cl 2 + 2Na 2 CO 3 + H 2 O 2NaHCO 3 +2NaCl+Cl 2 O Cl 2 O + H 2 O 2HOCl 2KClO 3 + 2H 2 C 2 O 4 K 2 C 2 O 4 + 2ClO 2 + 2CO 2 + 2H 2 O 12

13 ClO 2 F + HClO 4 Cl 2 O 6 + HF May decompose by: Cl 2 O 6 + H 2 O - HClO 4 + HClO 3 Cl 2 O 7 anhydride of perchloric acid Oxofluorides of chlorine, bromine, and iodine 13

14 trans-[f 2 BrO 3 ] - [F 5 IO 2 ] 2- H 5 IO 6 HIO 3 HClO 4 ClO 4 - HIO 4 14

15 Aqueous solution chemistry Potential diagrams 15

The Periodic Table consists of blocks of elements

The Periodic Table consists of blocks of elements s block d block p block There is a clear link between the Periodic Table and the electronic configuration of an element 1s 2s 2p 3s 3p 4s 3d 4p 1s ATOMIC