CHEMISTRY OF THE MAIN GROUP ELEMENTS

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CHAPTER 21

• CHEMISTRY OF THE MAIN GROUP ELEMENTS
• Problems All bold numbered problems

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Main Group elements 1,2, 13-18
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CHAPTER OVERVIEW

• This chapter examines the main group elements.
• Our primary focus will be to use the chemistry of
  these elements to review all of the topics we
  have covered in General Chemistry.

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CHAPTER OVERVIEW

• Read the chapter carefully and use it to review
  the fundamental concepts of chemistry.
• For example, names of certain industrial process
  may be involved in examination questions.

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THE PERIODIC TABLE A GUIDE TO THE ELEMENTS

• Valence Electrons
• The most significant factor in the behavior of
  these elements is the electronic configuration.
• Elements in the same group have the same
  configuration and same electron dot structure.
• Be able to calculate oxidation numbers

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THE PERIODIC TABLE

• Valence Electrons
• For the non-metals, the minimum oxidation number
  is equal to the group number minus 18.
• The elements become more metallic from top to
  bottom in a group, and from right to left in a
  period.
• Ionic Compounds
• Ionic compounds form between metals and
  non-metals.
• These compounds have formulas based on charge
  balance.

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THE PERIODIC TABLE

• Covalent Compounds
• The formulas of these compounds are based on
  sharing of electrons and not charge balance.
• The formulas for these compounds are difficult to
  predict and a variety of compounds usually exist.
  
• For example, there are more than six oxides of
  nitrogen that have been identified and
  characterized.

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21.2 Hydrogen

• Synthesis
• Commercially from methane gas and from the
  reaction with coke (graphite/coal).
• The latter is called syngas.
• In the laboratory
• acid metal
• metal water or base
• metal hydride water

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Calcium Hydride Hydrides have a -1 charge on
the hydrogen H-1 Only seen when H attached to a
metal (rare?)
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Water Gas or Syngas
100 years old
Modern method uses iron or cobalt oxides
Water gas shift reaction
Used for producing near pure hydrogen gas H2
400-500 oC
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Hydrogen

• Properties
• Ionic hydrides ( H-1), e.g. NaH, CaH2
• Covalent compounds (H), e.g. CH4
• Reactions to form ammonia and methanol

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21.3 SODIUM AND POTASSIUM

• These elements are in the alkali metals group.
  All the metals in this group have melting points
  below 200oC.
• Preparation and Properties
• Preparation from molten salts by electrolysis.
• Sodium forms the peroxide, Na2O2, when reacted
  with oxygen, and potassium forms the superoxide,
  KO2.

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SODIUM AND POTASSIUM

• Commercial Importance of Sodium Compounds
• Electrolysis of sodium chloride solution to
  produce sodium hydroxide and chlorine gas.
• Recall our discussion between the Brine vs-
  Molten Sodium process

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Solid NaCl
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CALCIUM AND MAGNESIUM

• Group 2A elements are called the alkaline earths.
  They form 2 ions and are easily oxidized.
• Magnesium is a low density metal that forms many
  very useful alloys.
• Since magnesium hydroxide is less soluble than
  calcium hydroxide, it will form when calcium
  hydroxide is added to a solution containing
  magnesium ion.

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Only Ca reacts with water, not Mg
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CALCIUM AND MAGNESIUM

• Magnesium Metallurgy is the process used to
  recover magnesium ion from sea water.
• The recovered magnesium hydroxide is converted to
  the chloride salt which is then electrolyzed to
  produce pure magnesium metal.
• Calcium is found in limestone, CaCO3, which can
  be converted to lime (quick lime), CaO, by
  heating (for cement) or Slake Lime Ca(OH)2
  (common reagent)

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Not soluble
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Hard Water
Limestone aka Scale which clogs pipes
Water Softener or Ion Exchange 2 ions bind more
tightly then 1 ions.
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ALUMINUM AND BORON

• Aluminum forms a 3 ion, is easily oxidized,
  but the oxide coating protects the metal
  rendering is passive in most cases.

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Aluminum Production

• The pure metal is prepared by electrolysis, the
  Hall process, but the ore must first be purified
  by the Bayer process.
• Abundance in earths curst
• O 45.5
• Si 25.7
• Al 8.37
• Fe 6.2

Aluminum is the most abundant metal in the earths
crust. Al is found in clay mainly as bauxite
Al2O3nH2O
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Bayer Process

• The first step is to separate bauxite from the
  iron(III)oxide and silicon dioxide relying on
  Al2O3 amphoteric characteristics.
• Treatment with base solubilizes the aluminum and
  silicon oxides (acids), leaving the basic
  iron(III)oxide as a solid.
• Treatment of the solution with carbonic acid
  forms the insoluble Al2O3, but leaves the silicon
  in solution as a hydroxo complex ion.

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Halls electrolysis process
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Gallium
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BORON

• Boron typically an alloy with other metals in
  conducting applications and building material,
  nuclear fuel rods to absorb neutrons.
• B2H6 has a unique hydrogen bridge structure.

Isolated 1963, called a 3 center 2 electron bond
Hydrogens weak dative bond, not like
H-bonding. This is stronger, though longer then
a normal covalent bond
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SILICON

• Used in brick, pottery, porcelain, lubricants,
  computer chips, and solar cells.
• Pure silicon is produced from silicon dioxide
  found in certain sands.
• Silicon dioxide
• The silicon is sp3 hybridized and forms a
  tetrahedron with four oxygen atoms.
• These basic units may be linked several ways.

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Silicates (SiO4)
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Mica
Silicates (SiO4)
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SILICON

• Silicates (SiO4)
• Portland cement, mica, feldspar, zeolite, etc.
• Silicone Polymers (-OSi(CH3)2-)n
• Calking, silly putty, lubricants, etc.

Oxygen atom not shown only Si vertices
Zeolite
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Silicone Polymers (-OSi(CH3)2-)n
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NITROGEN AND PHOSPHORUS

• N2(g) from air by liquefaction.
• P4(g) from calcium phosphate by reduction using
  carbon with silicon dioxide.
• Nitrogen Compounds
• Nitrogen takes on all oxidation states from -3 to
  5.
• Ammonia, Haber Process, from nitrogen and
  hydrogen gases (page 650)

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Nitrogen Compounds

• Hydrazine, Raschig Process, from ammonia and
  sodium hypochlorite. Used as a rocket fuel
• Hydrazine is used to treat chemical waste (to
  remove CrO4-2), and to remove dissolved oxygen
  (oxygen reacts with metals causing corrosion)
  from water in boiler tanks
• (N2H4 O2 ? N2 H2O)

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Nitrogen oxides, more than six exist.
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N2O fat soluble used to make whipping
cream. a.k.a. Laughing gas
N2O
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Pollution NO2

• NO2 is a brown gas often seen as a haze over
  large cities and is the source of acid rain

Brown gas seen when working with nitric acid
NO from car exhausts
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Nitrogen Compounds

• Nitric acid, Ostwald Process, from N2O4,
• Or from NO2 bubbled into water

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Phosphorus Compounds

• Phosphorus is made from calcium phosphate,
  silicon dioxide, and carbon in a phosphorus
  furnace.
• Phosphorus has a variety of uses
• Fertilizers, Detergents, Pesticides

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OXYGEN AND SULFUR

• Oxygen gas prepared from potassium chlorate (high
  purity)
• From liquefaction of air.
• N2 b.p. -196 ºC
• O2 b.p. -183 ºC

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OXYGEN AND SULFUR

• Ozone, O3, is a second, less stable allotrope of
  oxygen.
• Ozone absorbs the suns harmful ultraviolet
  radiation thereby protecting the earth from the
  sun
• Sulfur has more allotropes than any other
  element.
• The most common is S8 (this is a ring/cyclic
  compound.

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Compounds of Sulfur

• H2S(g) deadly, 100 ppm
• SO2, SO3, and H2SO4

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Plastic sulfur
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CHLORINE

• Laboratory preparation of chlorine gas from solid
  sodium chloride, sulfuric acid, and solid
  manganese(IV)oxide.
• Laboratory preparation of hydrogen chloride gas
  from solid sodium chloride and concentrated
  sulfuric acid.
• Oxy anions form in the 1, 3, 5, and 7 states.

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Brine Process for making NaOH (aq) and Cl2(g)
from sea-water
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CHLORINE

• Chlorine disproportionates in water to form Cl-
  and OCl-.
• In this reaction, chlorine is both oxidized and
  reduced.
• What is the oxidation state of each Cl?

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CHLORINE
Ammonium perchlorate (NH4ClO4) is unstable when
heated above 200 ºC since it contains an
oxidizing agent and a reducing agent.
NH4ClO4(s) ? N2(g) Cl2(g) O2(g)
4H2O(g) Sº 280J/K The space shuttle uses
this with Al powder for the solid engine
boasters. Half of all NH4ClO4 produced is used
by the space shuttle
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Catalytic destruction of Ozone by Cl