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Chapter 13. The Group 13 Elements. The Elements. History. Hans Christian Oersted (1777-1851) In 1825, 3K ( Hg ) + AlCl 3 ( s )  Al( s ) + 3KCl( s ) + Hg( l ) Friedrich W öhler (1800-1882) In 1827, 3K( l ) + AlCl 3 ( s )  Al( s ) + 3KCl( s ). Group Trends. Melting and boiling points

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chapter 13

Chapter 13

The Group 13 Elements

history
History
  • Hans Christian Oersted (1777-1851)
    • In 1825,

3K(Hg) + AlCl3(s)  Al(s) + 3KCl(s) + Hg(l)

  • Friedrich Wöhler (1800-1882)
    • In 1827,

3K(l) + AlCl3(s)  Al(s) + 3KCl(s)

group trends
Group Trends
  • Melting and boiling points
    • no apparent trend in melting points
    • decreasing trend in boiling points
group trends1
Group Trends
  • Melting and boiling points
    • each element has different arrangments in the solid phase

2180°C

660°C

30°C

157°C

303°C

Boron

Rhombohedral

Aluminum

CCP

Gallium

Orthorhombic

Indium

Tetragonal

Thallium

HCP

group trends2
Group Trends
  • Bond formation
    • favors covalent bond formation
      • high charge densities
group trends3
Group Trends
  • Bond formation
    • hydrated ions are the only stable ionic complexes
      • [Al(OH2)6]3+
      • [Ga(OH2)6]3+
      • [In(OH2)6]3+
      • [Tl(OH2)6]3+
group trends4
Group Trends
  • Oxidation states
    • B and Al only exhibit +3
    • Ga, In, and Tl exhibit both +3 and +1
      • +3 most common for Ga and In
      • +1 most common for Tl
    • can have a mixed oxidation state
      • GaCl2
        • [Ga]+[GaCl4]-
boron
Boron
  • Semimetal
    • mostly nonmetallic properties
  • Obtained by heating the oxide with magnesium

B2O3(s) + 3Mg(l)  2B(s) + 3MgO(s)

MgO(s) + 2H3O+(aq) + H2O(l)  [Mg(OH2)4]2+(aq)

boron1
Boron
  • Natural occurrence
    • found most in salts around volcanic areas
    • borax
      • Na2B4O7·10H2O
      • [B4O5(OH)4]2-
    • kernite
      • Na2B4O7·4H2O
boron2
Boron
  • Deposits
    • largest found at Boron, California
      • 10 km2
      • beds of kernite up to 50 m thick
boron3
Boron
  • Worldwide production
    • over 3 million tons
    • 35% used to manufacture borosilicate glass
      • Pyrex®
      • highly resistant to cracking under heat
boron4
Boron
  • 20% used to manufacture borax
    • cleaning agent
    • NaBO3 is now more commonly used
      • [B2(O2)2(OH)4]2-
boron5
Boron
  • Sodium peroxoborate

[B4O5(OH)4]2-(aq) + 4H2O2(aq) + 2OH-(aq)  2[B2(O2)2(OH)4]2-(aq) + 3H2O(l)

    • 5 x 105 tons produced annually
    • used in Europe as a bleaching agent
boron6
Boron
  • Control rods in nuclear power plants
    • strong absorber of neutrons
  • Wood preservatives
  • Fire-retardant in fabrics
  • Flux in soldering
borides
Borides
  • Binary compounds of boron
    • very hard
    • high melting
    • chemically resistant
  • Boron carbide
    • B4C (empirical)
    • B12C3
borides1
Borides
  • Boron carbide
    • one of the hardest substances known
    • high tensile strength
      • used in bulletproof clothing
      • bulletproof plates in armored vehicles
      • bicycle frames

2B2O3(s) + 7C(s)  B4C(s) + 6CO(g)

borides2
Borides
  • Titanium boride
    • TiB2

2TiO2(s) + B4C(s) + 3C(s)  2TiB2(s) + 4CO(g)

    • hexagonal layers of boron
  • Magnesium boride
    • superconducting
boranes
Boranes
  • Diborane
    • B2H6
    • 200 tons produced annually

2BF3(g) + 6NaH(s)  B2H6(g) + 6NaF(s)

    • highly reactive
    • toxic
    • colorless
boranes1
Boranes
  • Diborane
    • burns in air

B2H6(g) + 3O2(g)  B2O3(s) + 3H2O(g)

    • reacts with water

B2H6(g) + 6H2O(l)  2H3BO3(s) + 3H2(g)

    • undergoes hydroboration

B2H6(g) + 6CH2=CHCH3(g)  2B(CH2CH2CH3)3(l)

boranes2
Boranes
  • nido-boranes
    • BnHn+4
    • B10H14 (decaborane(14))
  • arachno-boranes
    • BnHn+6
    • B4H10 (tetraborane(10))
boranes3
Boranes
  • Was studied as a potential rocket fuel
  • Now, main interest is in their unique structures
    • B2H7-
    • B12H122-
sodium tetrahydridoborate
Sodium Tetrahydridoborate
  • NaBH4
    • BH4- used largely in organic synthesis
    • reducing agent

2NaH(s) + B2H6(g)  2NaBH4(s)

    • sodium chloride crystal structure
boron trifluoride
Boron Trifluoride
  • BF3
    • does not dimerize
    • one of the strongest single bonds known
      • 613 kJ/mol
boron trifluoride1
Boron Trifluoride
  • Used as a Lewis acid
    • dative covalent bonding
      • “to donate”
boron trichloride
Boron Trichloride
  • smallest of covalently bound chlorides
    • gas at room temperature
    • reacts vigorously with water

BCl3(g) + 3H2O(l)  H3BO3(aq) + 3HCl(aq)

boron neutron capture theory bnct
Boron Neutron Capture Theory(BNCT)
  • under investigation as a cancer therapy
    • radioactive source kills only cancerous cells
    • boron can easily capture a neutron
      • large cross-sectional area
slide28
BNCT
  • What happens?
    • the energy of this process propels the atoms through cells destroying them
    • problems occur in getting them to the malignant cells only
aluminum
Aluminum
  • Highly, negative reduction potential (-1.66V)
    • highly reactive

4Al(s) + 3O2(g)  2Al2O3(s)

aluminum1
Aluminum
  • Anodized
    • provides a thicker layer of the oxide
aluminum uses
Aluminum Uses
  • Construction metal
    • low density (2.7 g/cm3)
      • magnesium (1.7 g/cm3)
      • iron (7.9 g/cm3)
aluminum uses1
Aluminum Uses
  • Cookware
    • good conductor of heat
aluminum uses2
Aluminum Uses
  • Wiring
    • good conductor of electricity
aluminum chemical properties
Aluminum Chemical Properties
  • Burns with oxygen and other halogens

4Al(s) + 3O2(g)  2Al2O3(s)

2Al(s) + 3F2(g)  2AlF3(s)

  • Amphoteric

2Al(s) + 6H+(aq)  2Al3+(aq) + 3H2(g)

2Al(s) + 2OH-(aq) + 6H2O(l)  2[Al(OH)4]-(aq) + 3H2(g)

aluminum chemical properties1
Aluminum Chemical Properties
  • Hydrated ions

[Al(OH2)6]3+(aq) + H2O(l)  [Al(OH2)5(OH)]2+(aq) + H3O+(aq)

[Al(OH2)5(OH)]2+(aq) + H2O(l)  [Al(OH2)4(OH)2] +(aq) + H3O+(aq)

Aluminum chlorhydrate free

aluminum chemical properties2
Aluminum Chemical Properties
  • Formation of hydroxides

[Al(OH2)6]3+(aq) + 3OH-(aq)  Al(OH)3(s) + 6H2O(l)

Al(OH)3(s) + OH-(aq)  [Al(OH)4]-(aq)

  • Use as an antacid

Al(OH)3(s) + 3H+(aq)  Al3+(aq) + 3H2O(l)

aluminum availability
Aluminum Availability
  • Most abundant metal in the Earth’s crust
    • commonly found in clays
      • aluminum silicates
      • mixture of sodium, potassium, iron, calcium, magnesium, and aluminum silicates
    • also found in bauxite
      • impure hydrated aluminum oxide

Fe2Al9Si4O22(OH)2

Staurolite

extraction history
Extraction History
  • Henri Sainte-Claire Deville (1818-1881)
    • first to produce aluminum in 1854

AlCl3(s) + 3Na(s)  Al(s) + 3NaCl(s)

    • produced approximately 2 tons annually
    • price dropped 90% over 10 years
extraction history1
Extraction History
  • Hall-Héroult Process (1886)

P. Héroult

C.M. Hall

hall h roult process
Hall-Héroult Process
  • Purification of bauxite
    • digesting with caustic soda

Al2O3(s) + 2OH-(aq) + 3H2O(l)  2[Al(OH)4]-(aq)

    • insoluble Fe2O3 is filtered off as “red mud”
hall h roult process1
Hall-Héroult Process
  • With cooling, hydrated aluminum oxide precipitates

2[Al(OH)4]-(aq)  Al2O3·3H2O(s) + 2OH-(aq)

  • The hydrate is heated to give the anhydrous aluminum oxide

Al2O3·3H2O(s) + heat  Al2O3(s) + 3H2O(g)

hall h roult process2
Hall-Héroult Process
  • Synthesis of cryolite (Na3AlF6)

3SiF4(g) + 2H2O(l)  2H2SiF6(aq) + SiO2(s)

H2SiF6(aq) + 6NH3(aq) + 2H2O(l)  6NH4F(aq) + SiO2(s)

6NH4F(aq) + Na[Al(OH)4](aq) + 2NaOH(aq)  Na3AlF6(s) + 6NH3(aq) + 6H2O(l)

hall h roult process3
Hall-Héroult Process
  • Electrolysis of a cryolite-Al2O3 solution

2Al3+(cryolite) + 6e- 2Al(l)

3O2-(cryolite) + 3C(s)  3CO(g) + 6e-

hall h roult process4
Hall-Héroult Process
  • Four major by-products
    • red mud
      • NaOH solution is neutralized
      • Fe2O3 is used to extract pure iron
    • hydrogen fluoride gas

Al2O3(s) + 6HF(g)  2AlF3(s) + 3H2O(g)

      • aluminum fluoride is then dissolved in cryolite
hall h roult process5
Hall-Héroult Process
  • Four major by-products
    • carbon monoxide

2CO(g) + O2(g)  2CO2(g) + energy

      • burn with O2 to provide energy for powering the plant
    • fluorocarbons
      • 1 kg CF4 and 0.1 kg C2F6 produced for every 1 ton of Al
hall h roult process6
Hall-Héroult Process
  • Four major by-products
    • Fluorocarbons
      • fluorosilicic acid (H2SiF6)
        • fluoridation of water supplies

SiF62-(aq) + 8H2O(l)  H4SiO4(aq) + 4H3O+(aq) + 6F-(aq)

aluminum producers
Aluminum Producers
  • Major producers
aluminum uses3
Aluminum Uses
  • 25% in the construction industry
    • lightweight materials
  • 18% in the transportation industry
    • lower fuel consumption
  • 17% in the containers and packaging industry
    • soda cans
  • 14% in the power line industry
aluminum recycling
Aluminum Recycling
  • Uses less energy than the extraction of aluminum
    • melt in a smelter
aluminum halides
Aluminum Halides
  • AlF3
    • ionic (octahedral)
    • melts at 1290ºC
  • AlCl3
    • ionic character in the solid phase (hydrated octahedral)
    • covalent character in the liquid phase (dimer)
aluminum halides1
Aluminum Halides
  • AlBr3
    • covalent
    • melts at 97.5ºC
  • AlI3
    • covalent
    • melts at 190ºC
aluminum halides2
Aluminum Halides
  • AlCl3·6H2O
    • acidic due to hydrolysis

[Al(OH2)6]3+·3Cl-(aq) + H2O(l)  [Al(OH2)5(OH)]2+·2Cl-(aq) + H3O+(aq) + Cl-(aq)

  • AlCl3
    • exothermic reaction with water

AlCl3(s) + 3H2O(l)  Al(OH)3(s) + 3HCl(g) + heat

aluminum halides3
Aluminum Halides
  • AlCl3 as a catalyst in the Friedel-Crafts reaction
    • aluminum chloride acts as a strong Lewis acid

R—Cl + AlCl3 R+ + [AlCl4]-

    • carbocation reacts with an aryl compound

Ar—H + R+ Ar—R + H+

    • the catalyst is regenerated

H+ + [AlCl4]-  HCl + AlCl3

aluminum potassium sulfate
Aluminum Potassium Sulfate
  • Alum
    • KAl(SO4)2·12H2O

K2SO4 + Al2(SO4)3 + 24H2O  2KAl(SO4)2·12H2O

    • used as dyes
    • stops bleeding
spinel
Spinel
  • Magnesium aluminum oxide
    • MgAl2O4
spinels
Spinels
  • AB2X4
    • A is a dipositive metal ion
    • B is a tripositive metal ion
    • X is a dinegative anion
  • Indicate sites by t and o
    • (Mg2+)t(2Al3+)o(O2-)4
inverse spinels
Inverse Spinels
  • When the dipositive cation takes up some of the octahedral sites
    • Fe3O4
    • (Fe3+)t(Fe2+,Fe3+)o(O2-)4
spinels properties
Spinels Properties
  • Magnetic
    • Fe3+ (ferrites)
      • ZnxMn1-xFe2O4
  • Electrical
    • NaAl11O4
      • sodium atom is free to roam
      • high conductivity
biological aspects
Biological Aspects
  • Boron
    • Essential micronutrient in plants
      • dicots
      • monocots
    • Possible essential element in bone formation
biological aspects1
Biological Aspects
  • Aluminum
    • very toxic
      • 5 x 10-6 mol/L is sufficient to kill fish
      • a little higher in humans
        • anti-perspirant sprays
    • acidic soils release aluminum ions
      • decreases crop yields
biological aspects2
Biological Aspects
  • Thallium
    • is placed in the environment by coal-burning and cement manufacturers
    • highly toxic
      • mimics potassium