I. Group IVA

A. The Elements

1) Sn and Pb are metals known since antiquity

a) Sn alloy with Cu is Bronze (5000 yrs ago)

b) Pb used in Egyptian pottery glazes and Roman plumbing systems

2) Si is a metalloid with long-known oxide: Flint = SiO

The free element was identified by Berzelius in 1823

3) Ge is metalloid that was identified as “missing” by Mendeleev in 1871

Discovered in 1886 by Winkler

Ch 8 Main Group Elements continued

4) C is a nonmetal known as charcoal and diamond, not as an element until 1700’s

a) Isotopes:

i. 12C 98.9% is main component of “organic compounds”

ii. 13C 1.1% is an NMR active isotope

iii. 14C 1.2 x 10-10% is formed in the atmosphere and is radioactive

iv. 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

b) Allotropes

i. Diamond is the densest form

- Tetrahedral single bonds at all C

- Hardest of all natural substance

ii. Graphite is the thermodynamically most stable form

- Layers of fused 6-membered rings with all C sp2 hybridized

- Pi-bonding between layers allows lubrication and electrical conduction

H C n N 11

146

10

147

-147

146 e N C 5730 year half-life

Carbon Allotropes

c) Fullerenes = spherical or tubular C oligomers of 5- and 6 membered rings

i. Buckminsterfullerene = C60 discovered in 1985 (Nobel Prize)

ii. Found in nature at meteorite impact sites

iii. C70, C80, Carbon Nanotubes prepared soon after by Laser vaporization of graphite: Kroto, Curl, Smalley 1996 Nobel Prize in Chemistry

iv. Easily functionalized and used to trap small molecules

v. Hard to synthesize in large amounts

vi. Non-fullerene –C—C≡C—C≡C—C≡C— also identified in nature

d) Si and Ge also have diamond structures, but much weaker bonds

Ge(mp) = 945 oC while C(mp) = 4100 oC

B. Compounds

1) “Inorganic” Carbon Compounds

a) Carbon can be 5- or 6-coordinate (or even more) when bridging metals

Crystalline C60

b) Carbon Monoxide :C≡O:

i. Stable carbon with only 3 bonds

ii. Toxic gas byproduct of combustion; takes place of O2 in hemoglobin

c) Carbon Dioxide O=C=O

i. Component of the atmosphere; product of respiration and combustion

ii. Greenhouse effect = reabsorption of heat bouncing off Earth

- Carbon dioxide concentrations increasing since industrial revolution

- Global Climate change is predicted

d) Carbides = anionic carbon ions or clusters

i. C4- is simply called Carbide

ii. C22- is called acetylide

iii. C34- is called tricarbide

iv. Reactive ions

Al4C3 + 12 H2O ----> 4 Al(OH)3 + 3 CH4

CaC2 + 2 H2O ----> Ca(OH)2 + HC≡CH (exothermic, flame!)

2) Si 2nd most abundant (27%) on Earth’s crust (O = most abundant)

a) Semiconductors and Silicates (chapter 7)

b) Silanes = molecules with Si—Si bonds

i. Unstable because Si—Si (340 kJ/mol) weaker than C—C (368 kJ/mol)

ii. Si less electronegative than H (1.90 vs. 2.20) so attacked by Nu

iii. Si larger than C, which also makes it more easily attacked by Nu

iv. Empty d-orbitals act as e-pair acceptors

c) Ge, Sn, Pb all exhibit the Inert Pair Effect: PbX2, SnX2, etc…

II. Group VA

A. The Elements

1) As, Sb (metalloids) and Bi (metal) known since antiquity

a) Variety of allotropes for all of them

b) Bi is the heaviest nonradioactive element

2) P is a nonmetal first isolated from urine by Brandt in 1669

a) Glowed when exposed to air: “light bringing” = name

b) Has many solid allotropes

i. White P4 has cubic and hexagonal forms that react with air--store in H2O

ii. Red P has an amorphous structure and can be formed by heating white P

iii. Black P has 6-membered rings, converts to other forms at high Pressure

c) P4 tetrahedron in liquid and gas phasesP P

P

P

white

white

black

blackred

3) Nitrogen is a nonmetal diatomic gas making up 78.1% of Earths’ atmosphere

a) Isolated from air in 1772 by Rutherford, Cavendish, and Scheele

b) Colorless, odorless, nonreactive gas

i. :N≡N: structure has strong stable triple bond

ii. Used as inert atmosphere for performing chemical reactions

iii. N2(l) (bp = 77K) useful for cooling and trapping other compounds

c) Ions

i. N3- = azide = useful inorganic anion (like Cl- or Br-)

ii. N3- = nitride = strong ligand in some metal complexes (gives 6 e-)

iii. N22- = “pernitride” = long bond (122.4pm) compared to N2 (109.8pm)

iv. N5+ unstable cation prepared as [N5

+][AsF6-] in 1999

B. Compounds

1) Hydrides

a) Ammonia = NH3

i. Used as a fertilizer and in chemical synthesis and industry

ii. 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

N2 + 3H2 + catalyst ----> 2 NH3

b) Hydrazine = N2H4 used as rocket fuel

N2H4 + O2 ----> N2 + 2 H2O H = -622 kJ/mol

c) Phosphine = PH3 = poisonous gas

i. Weaker intermolecular attraction than NH3 (little H-bonding)

ii. mp, bp < NH3

iii. Phosphine derivatives (PR3) important Lewis Base Ligands

2) Nitrogen Oxides and Oxyions

a) Nitrous Oxide = N2O = dental anesthetic

i. Decomposes to N2 and O2 (nontoxic)

ii. Suspected greenhouse gas

b) Nitric Oxide = NO

i. Coordinating Ligand forms metal complexes

ii. Biological functions (Viagra helps regulate it)

c) N2O4 and NO2 Equilibrium

i. N2O4(g) 2 NO2(g) H = 57.3 kJ/mol

ii. N2O4 = colorless and diamagnetic

iii. NO2 = brown and paramagnetic

d) NOx Pollution

i. NO formed from atmospheric N2, O2 during fossil fuel combustion

ii. Can be oxidized to NO2; collectively they are known as NOx

iii. Acid Rain: 3 NO2 + H2O ----> 2 HNO3 + NO

e) Nitric Acid = HNO3 is an Industrially Important Acid

i. Used in the synthesis of ammonium nitrate fertilizer (much N content)

ii. Ammonium Nitrate is also an explosive

2 NH4NO3 ----> 2 N2 + O2 + 4 H2O

iii. Synthesis of nitric acid

4 NH3 + 5 O2 ----> 4 NO + 6H2O

2 NO + O2 ----> 2 NO2

3 NO2 + H2O ----> 2 HNO3 + NO

f) 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

III. Group VIA ChalcogensA. The Elements

1) Se = nonmetal important to the xerography industry as a photoconductor

2) Te = metalloid not important industrially

3) Po = radioactive metal discovered by Curie (1898) and used to power satellites

4) O = nonmetal diatomic gas making up 21% of Earth’s atmosphere, 46% crust

a) Discovered in 1770’s by Priestly

b) O2 is paramagnetic: 2p* __ __

c) Important in oxidation reactions

d) Respiration by binding to Hemoglobin

e) O3 form = Ozone shields Earth from UV = 200-360 nm

i. O3 is formed in the atmosphere form O2

O2 + h ----> 2 O

O + O2 ----> O3

ii. UV Protection: 2 O3 + h ----> 3 O2

iii. Ozone Depletion

NO2 + O3 ----> NO3 + O2 CF2Cl2 + h ----> CF2Cl + Cl

NO3 ----> NO + O2 Cl + O3 ----> ClO + O2

NO + O3 ----> NO2 + O2 ClO + O ----> Cl + O2

2 O3 ----> 3 O2 O3 + O ----> 2 O2

f) Liquid oxygen has a blue color due to absorption of light

g) Diamagnetic, red, O8 allotrope discovered 2006—unpaired O2 e- form bonding MO’s

Ground state

Excited states

5) S = yellow solid nonmetal

a) Known biblically as Brimstone

b) Makes gunpowder with KNO3 and charcoal

c) Many allotropes: -S8 orthorhombic is most stable

d) Viscosity of solid varies unexpectedly with temperature

e) Sulfuric Acid is the #1 Industrial Chemical (43.25 x 109 kg/yr in US)

i. Dense (d = 1.83 g/cm3), viscous, colorless liquid that burns skin

ii. Exothermic reaction with water (chars sugar by removing H2O)

iii. Synthesis: S + O2 ----> SO2 or MxSy + O2 ----> ySO2 + MxOy

SO2 + ½ O2 ----> SO3

SO3 + H2O ----> H2SO4

SS

S

SSS

S

S

ring----------->S8 chain---->S16 chain---->S24 chain

IV. Group VIIA HalogensA. The Elements

1) Salts known since antiquity as food preservatives (name = “salt former”)

2) Discovery as elements

a) Cl2 in 1630 by van Helmont (HCl known since ~900); toxic yellow gas (bleach smell)

b) I2 in 1811 by Courtois; purple solid that easily sublimes

c) Br2 in 1826 by Balard; red-brown liquid that easily vaporizes

d) F2 in 1886 by Moissan; so reactive it is hard to even handle

e) At2 in 1940 during particle collisions (radioactive with ½ life = only 8 hours)

3) Chemistry dominated by ready reduction to X-

a) Excellent oxidizing agents (is reduced itself); F2 is best of all elements

b) F is the most electronegative element, decreases down the group

c) I2 has the highest London Forces, which is why it is solid

4) Fluorine Discrepancies

a) Low bond energy in F2 makes it more reactive than expected

i. Extrapolate from others to 290 kJ/mol; actually 159 kJ/mol

ii. Repulsion of lone pairs responsible; also has long 143 vs. 128 pm bond

iii. MO explanation: poor overlap of small orbitals

b) HF weak acid: stronger H—F bonds not easily dissociated

F2 Cl2 Br2 I2

5) Polyatomic Ions

a) I2 + I- ----> I3- + other polyiodides

b) I2 + oxidizing agent ----> I2+ + I4

2+

6) Interhalogens: multiple possibilities and ways to synthesize them

a) Cl2 + F2 ----> 2 ClF

b) I2 + AgF ----> IF + AgI

7) Pseudohalogens = dimeric compounds with properties similar to X2

V. Group VIIIA Noble GasesA. The Elements

1) Discovery in 1766 by Cavendish

a) Nonreactive, leftover fraction of air (after N2, O2, CO2 all reacted)

b) Not separated from each other

2) He discovered in 1868 by Locklear and Frankland

a) New emission line observed during a solar eclipse

b) Helios = Greek for “sun”

c) Rare on Earth (Dexter, Kansas); used as NMR coolant (bp = 4.2 K)

d) Second most abundant in Universe ( H = 76%, He = 23%)

3) Ar discovered in 1890 by Rayleigh and Ramsay

a) N2 density discrepancies must be accounted for by a contaminant

b) Argon = “no work” because does not react

c) Used as chemically inert atmosphere, and for filling light bulbs

4) Ne, Kr, Xe discovered 1890’s by Ramsay and Travers

a) “Neon Lights” due to emission from gases when electricity passes through

b) “Hyperpolarized” 129Xe used as MRI contrast agent in lungs

5) Rn isolated from nuclear decay products in 1902

a) Product of Uranium decay in minerals

b) Enters homes through basements and floors

c) Radioactive and causes lung cancer (gas is inhaled)

B. Chemistry of Noble Gases

1) Thought to be inert because of filled valence shells

2) Clathrates = noble gas trapped in a cage of other molecules

a) Crystallized solvents under pressure; gas in cavities (1940’s)

b) He, Ne too small and never trapped yet

3) Bartlett, 1962 makes first true Noble Gas compounds

a) Xe + PtF6 ----> Xe+[PtF6]-

b) XeF2, XeF4 made soon after

c) Only Kr, Xe, Rn have been made into compounds so far, usually with F,O,Cl

4) Reactivity of Compounds

a) Fluoronating agents: 2 SF4 + XeF4 ----> 2SF6 + Xe

b) Oxidizing agents: XeO3 + 6 H+ + 6 e- ----> Xe + 3 H2O Eo = +2.10 V