Ozone: the “other” form of oxygen
 allotropes: different forms of an element in the same physical state
Ozone is a pollutant in the lower atmosphere, even though we don’t have enough of it in the upper
atmosphere!
In the upper atmosphere, UV light breaks bonds in O2, a process called photodissociation.
Marconi (1901) found evidence of free electrons in the upper atmosphere, formed by photoionization.
Free O atoms from photodissociation can combine with molecular oxygen to form ozone.
Meanwhile, ozone absorbs photons in the 240-310 nm range (UV), experiencing photodissociation.
If there were no ozone in the upper atmosphere, all of these UV photons would reach Earth’s surface.
Ozone Depletion
Freon-11 CFCl3 unreactive, water-insoluble
Freon-12 CF2Cl2 not removed from atmosphere in rainfall
e.g., CF2Cl2 + hν → CF2Cl· + Cl· (190-225 nm, 30 km altitude)
Cl· + O3 → ClO· + O2 (1)
rate = k (Cl)(O3); k = 7.2 × 109 M–1·s–1 @25 °C
2ClO· → 2 Cl· + O2
more Cl atoms free to attack more ozone
(2)
2×(1) 2 Cl· + 2 O3 → 2 ClO· + 2 O2
(2)
2 ClO· → 2 Cl· + O2
net:
Replacing CFCs: HFCs (hydrofluorocarbons; C–H replaces C–Cl)
Downsides:
 Some damage is already done and hard to fix
 Costly to replace CFCs with HFCs
 CFC substitutes less effective refrigerants than CFCs
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Highlights of other representative elements
Beryllium
 occurrence: beryl Be3Al2Si6O18 (light blue-green: aquamarine; deep green: emerald)
 preparation: electrolysis of fused beryllium chloride/fluoride
 largest use: structural parts in nuclear reactors; window for x-ray instruments
 No 8Be in measurable quantities because it is formed by combination of two 4He nuclei.
 large degree of covalency in bonding: in gas phase, linear BeCl2 molecules (sp hybridized)
Boron
 occurrence: borax Na2B4O7(H2O)10 (used in laundry detergents)
↓ H2SO4
H3BO3 (boric acid, used in eyewash)
↓Δ
B2O3
↓ SiO2
borosilicate glasses (e.g., Pyrex)
 boron halides are prototypical Lewis acids.

boron nitride (BN): isoelectronic with and isostructural with diamond; used in cutting tools.

boron hydrides: electron-deficient molecules (3-center, 2-electron bonding)

borohydride ion (BH4–): common reducing agent as lithium or sodium salt
Carbon
 occurrence: half in carbonates (minerals); the other half in plants, animals, CO2, coal, petroleum
 elemental forms: graphite (and graphene), diamond, fullerenes (C60, C70, C80), nanotubes
 carbides:
CaC2 + 2 H2O →
Al4C3 + 2 H2O →
 halides: CX4
also CHX3 (“haloform”), CH2X2 (“methylene halide”), CH3X
COCl2: “phosgene”, poison gas in WWI

urea: NH2CONH2; can be formed by heating ammonium cyanate (NH4OCN) as
discovered by Wöhler in 1844. Previously it was thought that it was
impossible to make an organic compound from an inorganic one.
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Nitrogen
 80% of the atmosphere is N2, but nitrogen is needed in –3 (NH3) and +5 (NO3–) oxidation states.
 Recent catalysis research has made it easier to “fix” nitrogen, but the traditional processes will
probably still be used for a long time. Nitrogen-fixing bacteria can also do the job.
o Haber process: uses hydrogen gas at 450 °C and 500 atm to prepare NH3
o Ostwald process: through a series of steps, converts NH3 to HNO3.
o The ammonia and nitric acid can be combined to form ammonium nitrate (a fertilizer,
over 300 million tons per year).

oxides:
N2O (N≡N–O), anesthetic/laughing gas
NO, formed in auto exhaust and in reactions of dilute nitric acid with copper
NO2, oxidation product of NO
HNO2, HNO3
 oxoacids:
Fluorine
 preparation: electrolysis of KF/HF (also produces hydrogen)

most important compound: HF (stored in Ni cylinders)

F2 will combine with hydrogen in all compounds to form HF.

HF is a “universal” solvent—it attacks everything!

Breakthrough in 1986: first chemical preparation of F2 (previously thought impossible)

UF6 used to separate 235UF6 from 238UF6 to purify uranium for early nuclear weapons.

SF6: insulating fluid in high-voltage transformers.

F– (as NaF) used for fluoridation of drinking water and toothpaste.
Ca5(PO4)3OH vs. Ca5(PO4)3F
apatite
fluoroapatite
Magnesium
 occurrence: seawater (MgCl2 and other salts)
 preparation: electrolysis of salts
 uses: *light structural alloys (with Zn, Al, Mn) [density = 1.74 g·cm–3 vs. 7.87 g·cm–3 for Fe]
*sacrificial anodes
*Grignard reagents: Mg + CH3Br → Br–Mg–CH3
 protected by MgO film
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Aluminum
 preparation: Hall-Heroult process (uses lots of electricity; it’s much more efficient to recycle
aluminum than to produce it from new ores)
 Al2O3 film protects the metal.
 LiAlH4 is a powerful reducing agent—stronger than NaBH4 due to weaker Al–H bonds.
 Al is amphoteric: reacts with acid or base.
o 2 Al + 6 HCl → Al2Cl6 + 3 H2
o 2 Al + 6 OH– → 2 AlO33– + 3 H2
 Al is the most abundant metal in the Earth’s crust (a question that was missed on Millionaire
once; you never know where this information might be useful!)
 Al can expand its valence shell (seemingly using vacant 3d orbitals), e.g., AlF63–
Silicon




occurrence: most abundant element in Earth’s crust (after oxygen)
preparation: SiO2 + 2 C → 2 CO + Si (98% pure) (3000 °C)
silicon dioxide aka quartz. Many impure forms (amethyst, opal…)
silicon carbide (SiC): diamond structure, very hard (9.5 vs. diamond’s 10 on Mohs scale)
SiO2 + 3 C → SiC + 2 CO (at 1950 °C; SiC decomposes at 2700 °C)
Phosphorus
 occurrence: phosphate rock (Ca3(PO4)2 and Ca5(PO4)3F); adenosine triphosphate
 reactions with oxygen: P4O6 or P4O10, depending on amount of oxygen
Sulfur
 occurrence: free on Gulf coast; sulfide ores (FeS, PbS, ZnS, Cu3FeS3); sulfates in seawater;
proteins (amino acid cysteine); coal
 allotropes include S8 rings (octagonal, puckered)
 oxides: SO2, SO3
 oxoacids: H2SO3, H2SO4, H2S2O7. Sulfuric acid the most important industrial chemical.
 hydride: H2S (weak acid, mp = –83 °C)
Chlorine
 occurrence: as NaCl (seawater)

preparation: electrolysis of NaCl(aq) or NaCl(l)

oxoacids: HOCl, HOClO, HOClO2, HOClO3 (strengths discussed in Chapter 16)
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A few other tidbits that every Principles of Chemistry alumnus should know
 Sr provides a crimson flame in fireworks. Ooh! Ahh!
Clearance Sale!
Something for Every
Element! Everything
Must Go!

BaSO4 is used in pigment that is opaque to x-rays.

Ga has one of the largest liquid ranges of all substances (mp = 30 °C;
bp = 2403 °C) and finds use in high-temperature thermometers.

In appears to have a +2 oxidation state in “InF2”, but is actually +1 and +3 as In[InF4].

Tl is a cumulative poison like Hg and Pb.

Ge was used in the original semiconductors, since replaced by Si.

Sn was known to the ancients; used in many alloys.
o bronze: 20% Sn; 80% Cu
o traditional solder: 50% Sn; 50% Pb

Pb was also known to the ancients.
o Pb(C2H5)4 a former antiknock agent in “leaded” gasoline.

As very poisonous, but traces needed in the body.

Bi is one of only two substances to expand on freezing.
o Bi is a much less toxic replacement for Pb in many applications.
o
209
Bi has the longest radioactive half-life known: 1.9×1019 years.

Se gives red color to glass; is also poisonous, but traces needed in the body.

H2Te is the worst-smelling inorganic compound.

Br2 is the only liquid nonmetal at room temperature.

A lack of iodine causes enlargement of the thyroid gland, known as goiter.
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