1

Chapter 16

Group 16 Elements

Physical Properties

The elements

Halides, oxohalides, oxides, salts of oxoacids

Metal sulfides, polysulfides, polyselenides, polytellurides

Compounds of sulfur and selenium with nitrogen

2

Relative abundances of the group 16 elements in the Earth’s crust

• Dioxygen makes up 21% of the Earth’s atmosphere and 47% of the Earth’s crust is composed of O-containing compounds (water, limestone, silica, silicates).

• Sulfur occurs around volcanoes and hot springs, iron pyrites fool’s gold (FeS2), and other minerals.

• Selenium and Tellurium are relatively rare and occur in only a few minerals

• Polonium is omitted because its abundance is only 3 × 10−7 ppb,

giving a negative number on the log scale.

Production of sulfur in the US from 1980 to 2008

3

Uses of sulfur and sulfuric acid

4

Given the ∆fHo(Na2O,s) = -414 kJ/mol, determine the enthalpy change for the process: 2Na+(g) + O2-(g) � Na2O(s)

Hint: Create an appropriate Born-Haber cycle and look up the necessary values for each of the steps.

Na2O (s)

2Na (s) + ½ O2(g) 2Na (g) + O (g)

2Na+ (g) + O2-(g)

2∆aHo(Na)

∆aHo(O)

2 IE1(Na) ∆EAHo1(O)

∆EAHo2(O)

∆latticeHo(Na2O,s)

∆fHo(Na2O,s)

5

Chemistry of oxygen

2H2O2 O2 + 2H2OMnO2 or Pt catalyst

2KClO3 3O2 + 2KCl∆, MnO2 catalyst

Describe bonding in [O2]+, O2, [O2]-, [O2]2- using MO theory.

O2 + PtF6 � [O2]+[PtF6]-

2O2F2 + 2BF3 � 2[O2]+[BF4]- + F2

The structures of O3 and [O3]−, and contributing resonance structures in O3.

• The O−O bond order in O3 is taken to be 3/2.

3/2 O2(g) → O3(g) ∆fHo(O3,g,298 K) = +142.7 kJ mol-1

O3(g) + 2H+(g) + 2e- ⇌ O2(g) + H2O(l) Eo = +2.07 V

Phosphite ozonide

Chemistry of ozone and ozonide

2KOH + 5O3 � 2KO3 + 5O2 + H2O

(Ozonide salts)

6

Sulfur: allotropes

S6 S7 S8

catena-S

structure of [S2I4]2+

S8 + 24F2→ 8SF6

S8 + 4Cl2→ 4S2Cl2

S8 + 4Br2→ 4S2Br2

SF6

7

Polysulfides, [Sx]2-, and polythionates are formed from reaction of sulfur

with hot aqueous alkali

polythionate

Vulcanization – soft rubber is toughened by cross-linking polyisoprene chains. Hydrocarbons are dehydrogenated when heated with sulfur and further reaction with alkenes occur.

Other reactions of sulfur:1/8 S8 + CO � O=C=S 1/8 S8 + CN- � N=C=S- ⇌ NΞC-S-

Na2SO3 + 1/8S8 –H2O, 373 K� Na2S2O3

S8 + 3AsF5 –liquid SO2 � [S8][AsF6]2 + AsF3

[S8]2+ is red and undergoes a change in ring conformation…

[S8]2+

8

• transannular interactions• Cross ring S-S separations

smaller than the sum of van der Waals radii

• Delocalized bonding

S82+

[S19]2+

• Two 7-membered, puckered rings connected by a 5-atom chain

• Charge localized on the three-coordinate S

SeleniumSelenium

Inorganic Chemistry By Egon Wiberg, Nils Wiberg, Arnold Frederick Holleman

4SeCl2 + 4Ph3PSe � Se8 + 4Ph3PCl2

9

telluriumtellurium

4+

2ReCl4 + 15Te + TeCl4 –heat in sealed tube→ 2[Te8][ReCl6]

H2O2 stabilizer

catalytic cycle used in the industrial manufacture of hydrogen peroxide

BaO2 + H2SO4 → BaSO4 + H2O2

2[NH4][HSO4] – electrolytic oxidation, “-H2” � [NH4]2[S2O8] � 2[NH4][HSO4] + H2O2

Production of H2O2

10

H2O2H2O2

H2O2H2O2

H2O2 + 2H+ + 2e- ⇌ 2H2O Eo = +1.78 VO2 + 2H+ + 2e- ⇌ H2O2 Eo = +0.70 V

Cl2 + H2O2 → 2HCl + O2

11

[V(O2)2(O)(bpy)]−

Peroxo complexes

[Mo2(O2)4(O)2(µ-OOH)2]2−

12

Polysulfanes: H2SXPolysulfanes: H2SX

2H2S + SnnCl2 � H2Sn+2 + 2HCl

n = 2

Polysulfides: [SX]2-Polysulfides: [SX]2-

[S6]2-

[Zn(S4)2]2- [Mn(S5)(S6)]

2-

[AuS9]2-

[(S6)Cu(µ-S8)-Cu(S6)]4-

13

1,2-diaminoethane, crypt-222

Polyselenides and polytellurides: [Sex]2- and [Tex]

2-Polyselenides and polytellurides: [Sex]2- and [Tex]

2-

3Se + K2Se2 K2[Se5]

4Se + K2Se2 + 2[Ph4P]Br [Ph4P]2[Se6] + 2KBr

3 Se + K2Se2 [K(15-crown-5)]2[Se5]

2K + 3 Te [K(crypt-222)]2[Te3]

DMF*

*DMF = Dimethylformamide =

DMF, 15-crown-5

[Te5]2- [Te8]

2-

O

FF

141 pm

103°

14

S2F10

SOF2

Sulfur fluorides and oxofluoridesSulfur fluorides and oxofluorides

15

Sulfur chlorides and oxochloridesSulfur chlorides and oxochlorides

1/4S8(l) + Cl2(g) -� S2Cl2206 pm

193 pm

Cl-S-S108°

Internal dihedral angle = 84°

Reaction Chemistry S2Cl2

2SO2 + S2Cl2 + 3Cl2 � 4SOCl2

SO3 + SCl2 � SOCl2 + SO2

2SCl2 � S2Cl2 + Cl2

SOCl2 SO2Cl2

Reaction Chemistry of SOCl2

RCO2H + SOCl2 �

RC(O)Cl + SO2 + HCl

16

SeF4TeF4 Se4Cl16

Tellurium halidesTellurium halides

17

MO diagram for octahedral [ECl6]2− (E = Se or Te)

Oxides of SulfurOxides of Sulfur

SOCl2 + Ag2S -430 K� S2O + 2AgCl

HS7H + SOCl2 → S8O

S8 ----CF3C(O)OOH → S8O

18

[SO2N3]- [(SO2)3N3]

-

19

Gas phase form of SO3 also exists as a trimer of SO4 units.

Solid state form exists as polymeric chains

Oxides of selenium and telluriumOxides of selenium and tellurium

[Te3O6F3]3-

SeO3 tetramer

20

Oxoacids and their salts: SOxoacids and their salts: S

H2O2 H2SO5 H2S2O8

ClSO3H-HCl

ClSO3H-HCl

H2S + HSO3Cl -low temp-� H2S2O3 + HCl

21

[S2O6]2− H2SO4 (g)

H2SO4 (l)

Sulfur-Nitrogen CompoundsSulfur-Nitrogen Compounds

22

Potential diagrams (values in V) for sulfur, selenium and tellurium at pH = 0.