Transcript CHAPTER 10

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
C(s) + H2O(g )  H2 (g ) + CO(g )
100 years old
Modern method uses iron or cobalt oxides
Catalytic steam reformation: 900-1000 C, near 100%
CH4 (g ) + H2O(g )  3H 2 (g ) + CO(g )
Water gas shift reaction
Used for producing near pure hydrogen gas H2
CO(g ) + H2O(g )  H2 (g ) + CO2 (g )
CO2 (g ) + CaO  CaCO3 (s)
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
N2 + H2  NH3
CO + 2H2  CH3OH
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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
Ca (aq) + 2HCO  CaCO3 (s) + H2O(l) + CO2
2+
3
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 earth’s curst
– O 45.5% Aluminum is the most
abundant metal in the earths
– Si 25.7
crust. Al is found in clay
– Al 8.37
mainly as bauxite Al2O3∙nH2O
– Fe 6.2
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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.
Step 1: add base
clay + H 2O  Al 2O3 (s) + SiO 2 (aq) + Fe +3 (aq) 

NaOH
Step 2: add acid
Fe(s) + Al(OH)-4 (aq) + SiO2 (aq) 
 Al2O3 (s) + SiO2 (aq)
H 2 CO3
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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Hall’s 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
Isolated 1963,
structure.
called a
3 center 2 electron
bond
Hydrogen’s 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.
Oxygen atom not shown
only Si vertices
Zeolite
Silicone Polymers (-OSi(CH3)2-)n
• Calking, silly putty, lubricants, etc.
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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
2NH3 (aq) + NaClO(aq)  N2 H4 (aq) + NaCl + H2O(l )
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
2HNO3 (aq)  2NO2 (g) + H 2O(l) + 1 O2 (g)
2
Brown gas seen when working with nitric acid
NO from car exhausts
2NO(g) + O2 (g)  2NO2 (g)
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Nitrogen Compounds
• Nitric acid, Ostwald Process, from N2O4,
2NaNO3 (s) + H2SO4 (aq)  2HNO3 (aq) + Na 2SO4 (s)
• Or from NO2 bubbled into water
NO2 (g) + H2O(l )  HNO3 (aq)
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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)
2KClO3 (s)  2KCl(s) + 3O2 (g)
catalyst
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 sun’s 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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S
U
L
F
U
R
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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.
Cl2 (g) + 2H2O  H3O + HClO(aq) + Cl (aq)
+
-
• 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∙
X = Cl, Br
X
O2
O3
XO + O
XO + O2
net
O3 + O
2O2
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