Chapter 20
The Representative
Elements
Section 20.1
A Survey of the Representative Elements
Reviewing the Periodic Table Regions
 Representative elements:
 Groups 1A – 8A (filling s and p orbitals)
 Transition metals:
 Center of the table (filling d orbitals)
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Section 20.1
A Survey of the Representative Elements
Reviewing the Periodic Table Regions
 Lanthanides and Actinides:
 Listed separately, on the bottom of the table
(filling 4f and 5f orbitals)
 Metalloids:
 Separate metals from nonmetals
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Section 20.1
A Survey of the Representative Elements
The Atomic Radii of Some
Representative Elements
(in Picometers)
Section 20.1
A Survey of the Representative Elements
CONCEPT CHECK!
Which should be the larger atom? Why?
Na
Cl
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Section 20.1
A Survey of the Representative Elements
CONCEPT CHECK!
Which should be the larger atom? Why?
Li
Cs
Section 20.1
A Survey of the Representative Elements
Distribution of the 18 Most Abundant Elements
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Section 20.1
A Survey of the Representative Elements
Abundance of Elements in the Human Body
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Section 20.2
The Group 1A Elements
Alkali Metals: Sources and Methods of Preparation
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Section 20.2
The Group 1A Elements
Group 1A Oxides
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Section 20.2
The Group 1A Elements
EXERCISE!
Predict the products formed by the following
reactants:
Na2O2(s) + H2O(l)
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→ NaOH(aq) + H2O2(aq)
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Section 20.3
The Chemistry of Hydrogen
Hydrides
 Binary compounds containing hydrogen:
 Ionic hydrides:
hydrogen + the most active metals
(eg; LiH, CaH2)
 Covalent hydrides:
hydrogen + other nonmetals
(eg; H2O, CH4, NH3)
 Metallic (interstitial) hydrides:
transition metal crystals treated with H2 gas
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Section 20.3
The Chemistry of Hydrogen
EXERCISE!
Predict the products formed by the following
reactants:
LiH(s) + H2O(l)
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→ H2(g) + LiOH(aq)
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Section 20.4
The Group 2A Elements
Alkaline Earth Metals
 Very reactive
 Great practical importance:
 Human life (Ca and Mg)
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Section 20.4
The Group 2A Elements
Selected Reactions of Group 2A Elements
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Section 20.4
The Group 2A Elements
Ion Exchange
 Ca2+ and Mg2+ are often removed during ion exchange,
releasing Na+ into solution.
 Ion exchange resin – large molecules that have many
ionic sites.
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Section 20.4
The Group 2A Elements
A Schematic Representation of a Typical Cation Exchange Resin
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Section 20.5
The Group 3A Elements
 Group 3A elements generally show the increase in
metallic character in going down the group that is
characteristic of the representative elements.
 B, Al, Ga, In, Tl
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Section 20.5
The Group 3A Elements
Some Physical Properties, Sources, and Methods of Preparation
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Section 20.5
The Group 3A Elements
Some Important Reactions
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Section 20.6
The Group 4A Elements
 Contains two of the most important elements on earth:
carbon and silicon.
 Can form four covalent bonds to nonmetals.
 CH4, SiF4, GeBr4
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Section 20.6
The Group 4A Elements
Some Physical Properties, Sources, and Methods of Preparation
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Section 20.6
The Group 4A Elements
Some Important Reactions
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Section 20.7
The Group 5A Elements
 Exhibits varied chemical properties.
 N, P, As, Sb, Bi
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Section 20.7
The Group 5A Elements
Some Physical Properties, Sources, and Methods of Preparation
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Section 20.8
The Chemistry of Nitrogen
Nitrogen
 The great stability of the NΞN bond means that most
binary compounds containing nitrogen decompose
exothermically to the elements.
NO2(g)
½N2(g) + O2(g)
ΔH° = –34 kJ
N2H4(g)
N2(g) + 2H2(g)
ΔH° = –95 kJ
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Section 20.8
The Chemistry of Nitrogen
Nitrogen Fixation
 The process of transforming N2 to other nitrogen–
containing compounds.
 The Haber Process:
N2(g) + 3H2(g)
2NH3(g)
ΔH° = –92 kJ
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Section 20.8
The Chemistry of Nitrogen
The Nitrogen Cycle
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Section 20.8
The Chemistry of Nitrogen
Nitrogen Hydrides
 Ammonia, NH3
 Fertilizers
 Hydrazine, N2H4
 Rocket propellant, manufacture of plastics,
agricultural pesticides
 Monomethylhydrazine, N2H3(CH3)
 Rocket fuels
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Section 20.8
The Chemistry of Nitrogen
Nitrogen Oxides

Nitrogen in its oxides has oxidation states from +1 to +5.
 In other compounds, nitrogen could have oxidation states of 1 to -3.
Compound
Oxidation State of N
N2O
+1
NO
+2
N2 O3
+3
NO 2
+4
HNO 3
+5
Section 20.8
The Chemistry of Nitrogen
Nitrogen Oxyacids
 Nitric acid, HNO3
hv
4HNO3 (l ) 
4NO2 (g ) + 2H2O(l ) + O2 (g )
 Nitrous acid, HNO2
HNO2 (aq )
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+

2
H (aq ) + NO (aq )
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Section 20.8
The Chemistry of Nitrogen
The Ostwald Process
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Section 20.9
The Chemistry of Phosphorus
Allotropes of Phosphorus
 White Phosphorus = P4 (tetrahedral) - very reactive
 Black Phosphorus = crystalline structure - much less
reactive
 Red Phosphorus = amorphous with P4 chains
heat, 1 atm, no air
P(white) 
 P(red)
P(white) or P(red) 
 P(black)
high pressure
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Section 20.9
The Chemistry of Phosphorus
Allotropes of Phosphorus
a) Pwhite
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b) Pblack
c) Pred
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Section 20.9
The Chemistry of Phosphorus
Phosphorus Oxyacids
 Phosphoric acid, H3PO4
 Phosphorous acid, H3PO3
 Hypophosphorous acid, H3PO2
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Section 20.10
The Group 6A Elements
 O, S, Se, Te, Po
 Although in Group 6A there is the usual tendency for
metallic properties to increase going down the group,
none of the Group 6A elements behaves as a typical
metal.
 Can form covalent bonds with other nonmetals.
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Section 20.10
The Group 6A Elements
Some Physical Properties, Sources, and Methods of Preparation
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Section 20.11
The Chemistry of Oxygen
Oxygen
 O2 makes up 21% of the Earth’s atmosphere.
 O3 (ozone) exists naturally in the upper atmosphere of
the Earth.
 Ozone layer absorbs UV light and acts as a screen to
prevent this radiation from penetrating to the
Earth’s surface.
 Scientists have become concerned that Freons and
nitrogen dioxide are promoting the destruction of the
ozone layer.
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Section 20.11
The Chemistry of Oxygen
Ozone
Section 20.12
The Chemistry of Sulfur
 Sulfur is found in nature both in large deposits of the
free element and in ores such as galena, cinnabar,
pyrite, gypsum, epsomite, and glauberite.
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Section 20.12
The Chemistry of Sulfur
Frasch Process
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Section 20.12
The Chemistry of Sulfur
Aggregates of Sulfur
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Section 20.12
The Chemistry of Sulfur
Sulfur Oxide Reactions
2SO2(g) + O2(g)
2SO3(g)
SO2(g) + H2O(l)
H2SO3(aq)
SO3(g) + H2O(l) H2SO4(aq)
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Section 20.13
The Group 7A Elements
Halogens
 All nonmetals: F, Cl, Br, I, At
 Because of their high reactivities, the halogens are not
found as free elements in nature. They are found as
halide ions (X–) in various minerals and in seawater.
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Section 20.13
The Group 7A Elements
Trends in Selected Physical Properties
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Section 20.13
The Group 7A Elements
Some Physical Properties, Sources, and Methods of Preparation
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Section 20.13
The Group 7A Elements
Preparation of Hydrogen Halides
H2(g) + X2(g)
2HX(g)
 When dissolved in water, the hydrogen halides behave
as acids, and all except hydrogen fluoride are completely
dissociated.
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Section 20.13
The Group 7A Elements
Halogen Oxyacids and Oxyanions
 All halogens except fluorine combine with various
numbers of oxygen atoms to form a series of oxyacids.
 The strengths of these acids vary in direct proportion to
the number of oxygen atoms attached to the halogen,
with the acid strength increasing as more oxygens are
added.
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Section 20.13
The Group 7A Elements
The Known Oxyacids of the Halogens
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Section 20.14
The Group 8A Elements
Noble Gases
 Filled s and p valence orbitals
 He and Ne form no compounds.
 Kr and Xe have been observed to form chemical
compounds:
Xe(g) + 2F2(g)
XeF4(s) [6 atm, 400°C]
XeF6(s) + 3H2O(l)
XeO3(aq) + 6HF(aq)
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Section 20.14
The Group 8A Elements
Selected Properties
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Section 20.14
The Group 8A Elements
CONCEPT CHECK!
Which of the following groups is the most reactive?
a) Group 1A Elements
b) Group 5A Elements
c) Group 6A Elements
d) Group 8A Elements
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Section 20.14
The Group 8A Elements
CONCEPT CHECK!
Which of the following groups does not contain at least
one element that forms compounds with oxygen?
a)
b)
c)
d)
e)
Group 4A Elements
Group 5A Elements
Group 6A Elements
Group 7A Elements
All of these groups contain at least one element
that forms compounds with oxygen.
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