Group IVA

1
Ch 8 Main Group Elements continued

• Group IVA
• The Elements
• Sn and Pb are metals known since antiquity
• Sn alloy with Cu is Bronze (5000 yrs ago)
• Pb used in Egyptian pottery glazes and Roman
  plumbing systems
• Si is a metalloid with long-known oxide Flint
  SiO
• The free element was identified by Berzelius in
  1823
• Ge is metalloid that was identified as missing
  by Mendeleev in 1871
• Discovered in 1886 by Winkler

2

• C is a nonmetal known as charcoal and diamond,
  not as an element until 1700s
• Isotopes
• 12C 98.9 is main component of organic
  compounds
• 13C 1.1 is an NMR active isotope
• 14C 1.2 x 10-10 is formed in the atmosphere and
  is radioactive
• Radiocarbon dating
• - 14C is incorporated into living things at the
  same ratio as it exists
• When dead, no more 14C incorporated and that
  present begins to decay
• Assign a date to the object based on how much 14C
  is left
• Allotropes
• Diamond is the densest form
• Tetrahedral single bonds at all C
• Hardest of all natural substance
• Graphite is the thermodynamically most stable
  form
• Layers of fused 6-membered rings with all C sp2
  hybridized

5730 year half-life
3
Carbon Allotropes
4

• Fullerenes spherical or tubular C oligomers of
  5- and 6 membered rings
• Buckminsterfullerene C60 discovered in 1985
  (Nobel Prize)
• Found in nature at meteorite impact sites
• C70, C80, Carbon nanotubes prepared soon after by
  Laser vaporization of graphite
• Easily functionalized and used to trap small
  molecules
• Hard to synthesize in large amounts
• Non-fullerene CCCCCCC also identified in
  nature
• Si and Ge also have diamond structures, but much
  weaker bonds
• Ge(mp) 945 oC while C(mp) 4100 oC
• Compounds
• Inorganic Carbon Compounds
• a) Carbon can be 5- or 6-coordinate (or even
  more) when bridging metals

5

• Carbon Monoxide CO
• Stable carbon with only 3 bonds
• Toxic gas byproduct of combustion takes place of
  O2 in hemoglobin
• Carbon Dioxide OCO
• Component of the atmosphere product of
  respiration and combustion
• Greenhouse effect reabsorption of heat bouncing
  off Earth
• Carbon dioxide concentrations increasing since
  industrial revolution
• Global Climate change is predicted
• Carbides anionic carbon ions or clusters
• C4- is simply called Carbide
• C22- is called acetylide
• C34- is called tricarbide
• Reactive ions
• Al4C3 12 H2O ? 4 Al(OH)3 3 CH4
• CaC2 2 H2O ? Ca(OH)2 HCCH
  (exothermic, flame!)
• Si 2nd most abundant (27) on Earths crust (O
  most abundant)

6

• Silanes molecules with SiSi bonds
• Unstable because SiSi (340 kJ/mol) weaker than
  CC (368 kJ/mol)
• Si less electronegative than H (1.90 vs. 2.20) so
  attacked by Nu
• Si larger than C, which also makes it more easily
  attacked by Nu
• Empty d-orbitals act as e-pair acceptors
• Ge, Sn, Pb all exhibit the Inert Pair Effect
  PbX2, SnX2, etc
• II. Group VA

7

• The Elements
• As, Sb (metalloids) and Bi (metal) known since
  antiquity
• Variety of allotropes for all of them
• Bi is the heaviest nonradioactive element
• P is a nonmetal first isolated from urine by
  Brandt in 1669
• Glowed when exposed to air light bringing
  name
• Has many solid allotropes
• White P has cubic and hexagonal forms that react
  with air (store in H2O)
• Red P has an amorphous structure and can be
  formed by heating white P
• Black P converts to the others at high Pressure

8

• Nitrogen is a nonmetal diatomic gas making up
  78.1 of Earths atmosphere
• Isolated from air in 1772 by Rutherford,
  Cavendish, and Scheele
• Colorless, odorless, nonreactive gas
• NN structure has strong stable triple bond
• Used as inert atmosphere for performing chemical
  reactions
• N2(l) (bp 77K) useful for cooling and trapping
  other compounds
• Anions
• N3- azide useful inorganic anion (like Cl- or
  Br-)
• N3- nitride strong ligand in some metal
  complexes (gives 6 e-)
• Compounds
• Hydrides
• Ammonia NH3
• Used as a fertilizer and in chemical synthesis
  and industry
• Nitrogen Fixation converting N2 into NH3
• Done under mild conditions by bacterial enzyme
• Done at 300 oC and 200 atm by Haber-Bosch
  Industrial Process
• Natural gas and energy expensive, but no better
  alternative yet

9

• Hydrazine N2H4 used as rocket fuel
• N2H4 O2 ? N2 2 H2O DH -622
  kJ/mol
• Phosphine PH3 poisonous gas
• Weaker intermolecular attraction than NH3 (little
  H-bonding)
• mp, bp lt NH3
• Phosphine derivatives (PR3) important Lewis Base
  Ligands
• Nitrogen Oxides and Oxyions
• Nitrous Oxide N2O dental anesthetic
• Decomposes to N2 and O2 (nontoxic)
• Suspected greenhouse gas
• Nitric Oxide NO
• Coordinating Ligand form metals
• Biological functions (Viagra helps regulate it)
• N2O4 and NO2 Equilibrium
• N2O4(g) 2 NO2(g) DH 57.3
  kJ/mol
• N2O4 colorless and diamagnetic

10

• NOx Pollution
• NO formed from atmospheric N2, O2 during fossil
  fuel combustion
• Can be oxidized to NO2 collectively they are
  known as NOx
• Acid Rain 3 NO2 H2O ? 2 HNO3 NO
• Nitric Acid HNO3 is an Industrially Important
  Acid
• Used in the synthesis of ammonium nitrate
  fertilizer (much N content)
• Ammonium Nitrate is also an explosive
• 2 NH4NO3 ? 2 N2 O2 4 H2O
• Synthesis of nitric acid
• 4 NH3 5 O2 ? 4 NO 6H2O
• 2 NO O2 ? 2 NO2
• 3 NO2 H2O ? 2 HNO3 NO
• Phosphoric Acid H3PO4 is also Industrially
  Important
• P4 5 O2 ? P4O10
• P4O10 6 H2O ? 4 H3PO4
• Ca3(PO4)2 3 H2SO4 ? 2 H3PO4 3 CaSO4

11

• Group VIA Chalcogens
• The Elements
• Se nonmetal important to the xerography
  industry as a photoconductor
• Te metalloid not important industrially
• Po radioactive metal discovered by Curie (1898)
  and used to power satellites
• O nonmetal diatomic gas making up 21 of
  Earths atmosphere, 46 crust
• Discovered in 1770s by Priestly
• O2 is paramagnetic p2p __ __
• Important in oxidation reactions
• Respiration by binding to Hemoglobin
• O3 form Ozone shields Earth from UV 200-360
  nm
• O3 is formed in the atmosphere form O2
• O2 hn ? 2 O
• O O2 ? O3
• UV Protection 2 O3 hn ? 3 O2
• Ozone Depletion
• NO2 O3 ? NO3 O2 CF2Cl2 hn ?
  CF2Cl Cl
• NO3 ? NO O2 Cl O3 ? ClO O2
• NO O3 ? NO2 O2 ClO O ? Cl
  O2

12

• S yellow solid nonmetal
• Known biblically as Brimstone
• Makes gunpowder with KNO3 and charcoal
• Many allotropes a-S8 orthorhombic is most stable
• Viscocity of solid varies unexpectedly with
  temperature
• Sulfuric Acid is the 1 Industrial Chemical
  (43.25 x 109 kg/yr in US)
• Dense (d 1.83 g/cm3), viscous, colorless liquid
  that burns skin
• Exothermic reaction with water (chars sugar by
  removing H2O)
• Synthesis S O2 ? SO2 or MxSy O2
  ? ySO2 MxOy
• SO2 ½ O2 ? SO3

ring-----------gtS8 chain----gtS16 chain----gtS24
chain
13

• Group VIIA Halogens
• The Elements
• Salts known since antiquity as food preservatives
  (name salt former
• Discovery as elements
• Cl2 in 1630 by van Helmont (HCl known since
  900) toxic yellow gas (bleach smell)
• I2 in 1811 by Courtois purple solid that easily
  sublimes
• Br2 in 1826 by Balard red-brown liquid that
  easily vaporizes
• F2 in 1886 by Moissan so reactive it is hard to
  even handle
• At2 in 1940 during particle collisions
  (radioactive with ½ life only 8 hours)
• Chemistry dominated by ready reduction to X-
• Excellent oxidizing agents (is reduced itself)
  F2 is best of all elements
• F is the most electronegative element, decreases
  down the group
• I2 has the highest London Forces, which is why it
  is solid
• Fluorine Discrepancies
• Low bond energy in F2 makes it more reactive than
  expected
• Extrapolate from others to 290 kJ/mol actually
  159 kJ/mol
• Repulsion of lone pairs responsible also has
  long 143 vs. 128 pm bond
• MO explanation poor overlap of small orbitals
• b) HF weak acid stronger HF bonds not easily
  dissociated

14

• Polyatomic Ions
• I2 I- ? I3- other polyiodides
• I2 oxidizing agent ? I2 I42
• Interhalogens multiple possibilities and ways
  to synthesize them
• Cl2 F2 ? 2 ClF
• I2 AgF ? IF Ag I
• 7) Pseudohalogens dimeric compounds with
  properties similar to X2

15

• Group VIIIA Noble Gases
• The Elements
• Discovery in 1766 by Cavendish
• Nonreactive, leftover fraction of air (after N2,
  O2, CO2 all reacted)
• Not separated from each other
• He discovered in 1868 by Locklear and Frankland
• New emission line observed during a solar eclipse
• Helios Greek for sun
• Rare on Earth (Dexter, Kansas) used as NMR
  coolant (bp 4.2 K)
• Second most abundant in Universe ( H 76, He
  23)
• Ar discovered in 1890 by Rayleigh and Ramsay
• N2 density discrepancies must be accounted for by
  a contaminant
• Argon no work because does not react
• Used as chemically inert atmosphere, and for
  filling light bulbs

16

• Ne, Kr, Xe discovered 1890s by Ramsay and
  Travers
• Neon Lights due to emission from gases when
  electricity passes through
• Xenon used as MRI contrast agent in lungs (NMR
  active isotope)
• Rn isolated from nuclear decay products in 1902
• Product of Uranium decay in minerals
• Enters homes through basements and floors
• Radioactive and causes lung cancer (gas is
  inhaled)
• Chemistry of Noble Gases
• Thought to be inert because of filled valence
  shells
• Clathrates noble gas trapped in a cage of other
  molecules
• Crystallized solvents under pressure gas in
  cavities (1940s)
• He, Ne too small and never trapped yet
• Bartlett, 1962 makes first true Noble Gas
  compounds
• Xe PtF6 ? XePtF6-
• XeF2, XeF4 made soon after
• Only Kr, Xe, Rn have been made into compounds so
  far, usually with F,O,Cl
• Reactivity of Compounds
• Flouronating agents 2 SF4 XeF4 ? 2SF6
  Xe