AirEarth Crust

Oxygen on EarthOxygen on EarthH2O (oceans)

O2, CO2 (atmosphere)

CO3 (rocks, coral, seashells)

SiO2, silicates (sand, clay, rocks)

Made commercially by fractional distillation of air (b.p. = 90K)

Oxygen Content

ALLOTROPES OF OXYGEN

Ozone (O3) is a strong oxidizing agent, highly toxic

Kills bacteria (replacement for Cl2 in municipal water treatment)

Irritating component of photochemical smog

O2 Paramagnetic (why?)

O3 Higher energy form - important UV absorber

in the stratosphereLight or

electrical discharge

3O2 2 O3

decomposition

OXYGEN IONSOxide Ion O2 (most compounds)

e.g. Li2O = 2Li+ O2

Peroxide Ion O22 = O – O

e.g. Na2O2 = 2 Na+ O – O

Also, H2O2 (hydrogen peroxide)

Superoxide Ion O2

e.g. KO2 = K+ O2

Can have positive oxidation states in combination with fluorine

+ 2 in OF2

HYDROGEN PEROXIDE• Strong oxidizing agent

(30-85% solutions) e.g. bleaching wood pulp to produce white paper• Hair bleach (~6% solution)• Antiseptic (3% solution)

H2O2 decomposition can be explosive:

2 H2O2 2 H2O + O2 H = 200 kJ/mol

(disproportionation reaction)

HYDROGEN PEROXIDE

Reduction to H2O:

H2O2 + 2H+ + 2I I2 + 2H2O

Oxidation to O2:

2MnO4 + 5 H2O2 + 6H+ 2Mn2+ + 5O2 + 8H2O

SULFUR

Sources:

Sulfide Minerals (S2-):

FeS2 (Pyrite) - Iron Ore (Fool’s Gold)Cu3FeS3 (Bornite) - Source of CuPbS (Galena) - Source of PbZnS (Zinc Blende) - Source of Zn

Sulfate Minerals (SO42-)

e.g. Na2SO4, MgSO4

Also, CaSO4 · (H2O)2 (Gypsum)Used for wallboard, plaster of Paris.

COMMERCIAL SOURCES OF SULFUR

1) Sulfur Mines – Along Gulf of Mexico, deposits of S8 Frasch Process.

2) Byproduct from other manufacturing processes.a) Production of Zn, Pb, and Cu from their sulfide ores.b) Petroleum – 3% S.c) Coal – 5%.

SO2 forms when coal is burned.

SO2 + H2O H2SO3

Acid RainSO2 +[O] SO3 +H2O H2SO4

CaCO3 + H2SO4 CaSO4 + H2O + CO2

(Marble)

Sulfur

Two allotropes

S8 yellow, cyclic

Polymer Sx red-brown

polymer: zigzag chains of sulfur atoms

S8(s) S8(l) SSSSSSS

T> 150CMelts at 113C

Sulfur

Common Oxidation States

+6 SO3; H2SO4 (sulfuric acid)can’t be oxidizedcan only be reduced

+4 SO2; H2SO3 (sulfurous acid)can be both oxidized AND reduced

-2 H2S; S2-

can’t be reducedcan only be oxidized

Compounds of S• H2SO4 most important industrial chemical

• H2S (rotten egg smell) (S2- )source: metal sulfides + strong acid

e.g. ZnS + HCl ZnCl2 + H2S(g)– poisonous– tarnishes Ag in presence of O2

4Ag + 2H2S + O2 2Ag2S + 2H2O– Organic sulfides, e.g. C4H9SH

Strong odor – added to natural gas

• S2O32- (thiosulfate)

used in photography: forms water soluble complexes with Ag

Uses of H2SO4

• Making phosphate fertilizer

Ca3(PO4)2 + 3H2SO4 3CaSO4 + 2H3PO4

~65% of H2SO4

• Manufacture of chemicals• Metal refining• Petroleum refining (as catalyst)• Strong oxidizing agent• Drying agent

Selenium, TelluriumSource: metal sulfides

byproducts of Cu, Pb refiningUses: semiconductors

e.g. Se: Has low electrical conductivity in the dark which increases in light - photoconductor

Used in photocopiers, light meters in cameras

Compounds: form covalent bondsOxides and hydroxides are acidic (typical of nonmetals)

Se non metalTe semi-metalPo metal

Nitrogen

Nitrogen (N2) is very unreactivetriple bond energy = 941kJ/mol

Sourcefractional distillation of air

(78% of air is N2)

KNO3 water soluble salts

NaNO3 found in deserts

Nitrogen fixation: formation of N containing compounds from N2

N is an essenial element in proteins, nucleic acids& necessary to maintain soil fertility

Compounds of NitrogenCompounds of Nitrogen

Oxidation states of 3 to +5

Compounds with H

1. NH3 (3 oxidation state)

2. N2H4 (2 oxidation state)

strong reducing agent:

N2H4 N2(g) + 2 H2(g) H =

forms N2 readily: S = +

3. Dimethyl hydrazine (rocket fuel)

N compounds with oxygenN compounds with oxygen

N2O colorless, odorless gas

used as anesthetic (laughing gas)propellant in whipping cream

NO formed in car engines: N2 +O2 2NO

N2O3 blue solid, decomposes: N2O3 NO + NO2

NO2 brown gas; component of smog

N2O4 2NO2 N2O4

N2O5 unstable, decomposes to NO2

HNO3

Produced from NH3 by Ostwald process (catalytic oxidation).

Uses: fertilizer

NH3 + HNO3 NH4NO3(s)strong acidstrong oxidizing agent.cleaning agentto make explosives

(e.g. nitroglycerine, TNT)

Hydrolysis of oxides

Hydrolysis: reaction with water

N is a non metal: oxides are acidic.

Oxide + H2O = hydroxide

N2O3 + H2O 2HNO2 (nitrous acid)

3NO2 + H2O 2HNO3 + NO

N2O5 + H2O 2HNO3 (nitric acid)

PHOSPHORUSPHOSPHORUS

Source: Phosphate Minerals

Ca3(PO4)2 contains PO43- (tetrahedral P)

P is made by heating Ca3(PO4)2 and coke in an electric furnace.

2Ca3(PO4)2(s) + 10C(s) + 6SiO2 6CaSiO3(s) + 10CO(g) + P4(g)Two allotropes:

White P: P

4

, tetrahedral

Red P: Polymeric

P

P

P P

P

P

P P

P

P

White phosphorus (P4) burns spontaneously in air.

P4(s) + 5O2(g) P4O10

H = 3000 kJ/mole

Red phosphorus (polymeric) is more stable. Not volatile.Does not react with air at 25°C.

PHOSPHORUS ALLOTROPES

Red P White P

600

o

C

Let Stand

OXIDES OF PHOSPHORUSOXIDES OF PHOSPHORUS

PHOSPHORUS OXYACIDSPHOSPHORUS OXYACIDS

P4O10 + 6H2O 4H3PO4 phosphoric acid

P4O6 + 6H2O 4H3PO3 phosphorous acid

Also H3PO2 hypophosphorous acid

USES OF PHOSPHORUSUSES OF PHOSPHORUS

FertilizerP is essential for plant growth

Ca3(PO4)2 + 3H2SO4 2H3PO4 + 3CaSO4

H3PO4 + 3NH3 (NH4)3PO4

Detergent

Complexes metal ions

Biological molecules (DNA, RNA)

Biochemical energy source (ATP)

COMPARISONS IN GROUP VCOMPARISONS IN GROUP V

Nitrogen N2(g) NNNH3 is stable.

Non-metal oxides dissolve to give acidic solutions

N2O3 + H2O 2HNO2

N2O5 + H2O 2HNO3

3NO2 + H2O 2HNO3 + NO

PHOSPHORUSPHOSPHORUS

Allotropes: White P P4, tetrahedral. Red P polymer.

PH3 burns in air.

Non-metal oxides dissolve to give acidic solutions:

P4O10 + 6H2O 4H3PO4

P4O6 + 6H2O 4H3PO3

ARSENICARSENIC

Allotropes:Yellow As As4

Gray As brittle solid.

AsH3 ignites spontaneously in air.

As4O10 – acidic oxide:

As4O10 + 6H2O 4H3AsO4

As4O6 is amphoteric, but is more soluble in base.

ANTIMONY – SbANTIMONY – Sb

Brittle gray metalloid.Sb4O6 is amphoteric.There is no Sb4O10.

Bismuth is a metal.Bi4O6 is basic and dissolves only in acids.Bi(OH)3 is basic.Bi5+ is rare.

BISMUTH - BiBISMUTH - Bi

OXIDATION STATES

P5+ dominates.As3+, As5+ are equally common.Sb3+ dominates.Bi3+ dominates.

Inert Pair Effect

HYDRIDE STABILITY

NH3 is stable.PH3 is stable but burns in air.AsH3 decomposes easily.SbH3, BiH3 are very unstable.

GROUP V TRENDS

Going down the periodic table:

1) Electronegativity decreases.2) Switch from non-metallic to metallic.3) Hydroxides and oxides become more basic.4) Hydrides become less stable.5) “Inert pair effect” becomes more pronounced: +3

becomes more stable as compared to +5.

CARBON and Group IV

Carbon Sources:

1) Elemental form – coal.

2) Carbonate rocks (CO32-)

Limestone, marble, chalk = CaCO3

Dolomite = MgCO3

ALLOTROPIC FORMS OF CARBONALLOTROPIC FORMS OF CARBON

1) Diamond - used as abrasive, in drill bits and cutting tools, and as a gem.

2) Graphite - used in batteries, pencils, and lubricants.

3) Fullerenes - More recently discovered molecules such as C60 which has the shape of a soccer ball.

Carbon Black – SootAmorphous form of carbon used in

tires, inks, pigments, and carbon paper.

CARBIDESCARBIDES1) Ionic Carbides

Contain C4- or C22- (-CC-)

C4-: Be2C, Al4C3 react with water to give CH4.

C2 2-(-CC-): CaC2 reacts with water to give HCCH.

2) Covalent Carbides Carbon is bound covalently to a metal or metalloid.SiC - almost as hard as diamond, does not react w/water

3) Interstitial CarbidesMetals with carbon atoms found in between the metal atoms in the structure.Steel – often harder than the pure metal.

SILICONSILICON

Second most abundant element.Found in combination with O.

Silicate Minerals: [Si2O52-]n, SiO4

4-

Sand: SiO2 (this is also quartz).With aluminum in aluminosilicates (clay, feldspars).

Prepared by:

SiO2(s) + 2C(s) Si(l) + 2CO(g) (3000C)sand coke 98%

Very pure silicon (<1 ppb impurity) is required for electronics applications.

GROUP IV TRENDSGoing down the periodic table:

1) The +2 oxidation state becomes more stable than +4 due to the “inert pair” effect.

+2 is rare for C, Si, Ge.+2 in some compounds, +4 most common for Sn.+4 is unstable for Pb strong oxidizing agent (PbO2)

2) Basicity of oxides and hydroxides increases.CO2, SiO2, GeO2 are weakly acidic.SnO, SnO2, PbO are amphoteric.

3) Hydrides become less stable.Enormous number of stable hydrocarbons.SiH4 is stable but is spontaneously flammable.

Ge, Sn, Pb hydrides are very unstable.

Orbital Hybrids and Valence

Li

Na

Be

Mg

B

Al

C

Si

N

P

O

S

F

Cl

2p

3p

2s

3s

The differences between the 2nd and 3rd periods:

2nd period: Only s and p orbitals are possible with n = 2

Therefore, the maximum number of bonds is 4 (single and/or double bonds)

Examples: CH4, NF4+, BH4

-

3rd (and higher periods): can use d-orbitals to make bonds

E.g. PF5 P atom is sp3d

SF6 S atom is sp3d2

Let’s look at valences:

N can gain 3 electrons or lose 5 to make an octet

But, N can only make 4 bonds (maxiumum for n=2)

Therefore N usually has a valence of 3

(NH3, NCl3, CH3NH2 - all have 3 bonds and one lone pair on the N atom)

N with oxidation state 5 never has more than four bonds:

Oe.g., NO3

- N=O (4 bonds to N) O

NO2+ O=N=O (4 bonds to N, like CO2)

Likewise, O usually makes 2 bonds: H2O, OF2, H2C=O

Likewise, C can gain 4 or lose 4 electrons to make an octet (valence = 4)

So carbon always makes 4 bonds

CH4 (4 single bonds)

O=C=O (2 double bonds)

H-CC-H (1 single + 1 triple bond)

H2N C=O (2 single + 1 double bond)

H2N (urea)

What about 3rd (and higher) periods - Si, P, S…?

For these elements, double bonds are very uncommon (usually only single bonds)

Si, P, S, ... Compounds have only

Ge, As, Se, ... single bonds (double and

Sn, Sb, Te, ... triple are very rare)

Reason: atoms past second row are too big

C C

good sideways

overlap of p orbitals

(double and triple bonds OK)

Si Si

poor overlap of p orbitals

---- no multiple bonds

(can still make single bonds)

So CO2 is molecular (O=C=O, has double bonds)

But SiO2 (quartz, sand, glass…) is a 3-dimensional solid network:

O2 is molecular (O=O, has a double bond)

But S forms rings (e.g., S8)

Nitrogen (N2) has a triple bond NN (very stable molecule)

But phosphorus is found in several forms (white, red, black), all of which have only single bonds.

The chemistry of carbon is unique because:

• It has a valence of 4 (highest in 2nd period)

• It can make stable bonds with itself

• It can make multiple bonds to C, N, O

• The C-H bond is nonpolar, but bonds to other elements (N, O, halogens) are polar

This is why life is based on the chemistry of carbon (organic chemistry)