Chapter 20
The Representative
Elements
Section 20.1
A Survey of the Representative Elements
The Atomic Radii of
Some
Representative
Elements (in
Picometers)
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Section 20.2
Atomic
The
Group
Masses
1A Elements
Reaction of Group 1A Metals
• Reactions with water:
2Li(s) + 2H2O → 2LiOH + H2
2Na(s) + 2H2O → 2NaOH + H2
2K(s) + 2H2O → 2KOH + H2
2Rb(s) + 2H2O → 2RbOH + H2
2Cs(s) 2H2O → 2CsOH + H2
(aq)
(aq)
(aq)
(aq)
(aq)
2X(s) 2H2O → 2XOH + H2
(aq)
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Section 20.2
Atomic
The
Group
Masses
1A Elements
Reaction of Group 1A Metals
• In the presence of excess oxygen:
4Li + O2 → 2Li2O
2Na + O2 → Na2O2
K + O2 → KO2
Rb + O2 → RbO2
Cs + O2 → CsO2
• In the presence of a halogen:
2Na + Cl2 → 2NaCl
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Section 20.2
Atomic
The
Group
Masses
1A Elements
Reactions of Group 1A Oxides
In water…
• oxides form hydroxides
Li2O + H2O → 2LiOH
•
peroxides form hydroxides and hydrogen peroxide
Na2O2 + 2H2O → 2NaOH + H2O2
• superoxides form hydroxides and hydrogen peroxide and
oxygen
2KO2 + 2H2O → 2KOH + 2H2O2 + O2
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Section 20.2
Atomic
The
Group
Masses
1A Elements
Reactions of Group 1A Oxides continued…
• In dilute acid, instead of a base forming, an acid-base
reaction occurs and forms a salt and the other products
from reaction with water.
Li2O + HCl → LiCl + H2O
Na2O2 + HCl → NaCl + H2O2
KO2 + HCl → KCl + H2O2 + O2
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Section 20.3
The Chemistry
Mole
of Hydrogen
Hydrides
• Binary compounds containing hydrogen:
 Ionic hydrides:
hydrogen + the most active metals (group I and group II)
(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
Mole
of Hydrogen
Exercise
Predict the products formed by the following
reactants:
LiH(s) + H2O(l) → H2(g) + LiOH(aq)
Ionic hydrides react with water to produce hydrogen gas and a
hydroxide.
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Section 20.3
The Chemistry
Mole
of Hydrogen
Reaction of Group 2A Metals
• Reactions with water:
Be has no rxn with water
Mg(s) + H2O(l) → Mg(OH)2 + H2
Ca(s) + 2H2O(l) → Ca(OH)2 + H2
Sr(s) + 2H2O(l) → Sr(OH)2 + H2
(s)
(aq)
(aq)
More reactive with water as you go down the group
X(s) + 2H2O → X(OH)2 + H2
(aq)
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Section 20.4
The Group 2A Elements
Reactions of Group 2A Metals
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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
• Notice that Boron is a nonmetal!
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Section 20.5
The Group 3A Elements
Some Important Reactions
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Section 20.5
The Group 3A Elements
Complex ion formation of Al
•
Al(H2O)63+ ↔ Al(OH)(H2O)52+ + H+
• Salt that produces an acidic solution
• Lewis acid base reaction
What species is acting as the Lewis acid? Lewis base?
Al
OH-
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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 20.8
The Chemistry of Nitrogen
• Exhibits varied chemical properties.
• N, P, As, Sb, Bi
• Compounds of N
– NH3 NF3 only 3 bonds total
• Compounds of P
– PH3, PF3, but also PF6
How???
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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)
∆Ho = -92 kJ
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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
N 2O
NO
N 2O 3
NO 2
HNO 3
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Oxidation State of N
+1
+2
+3
+4
+5
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Section 20.8
The Chemistry of Nitrogen
Nitrogen Oxyacids
• Nitric acid, HNO3 (strong acid)
hv
4HNO3 (l ) 
4NO2 (g ) + 2H2O(l ) + O2 (g )
• Nitrous acid, HNO2 (weak acid)
HNO2 (aq )
+

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
Phosphorus Oxyacids
• P4O10 + H2O → H3PO4 (phosphoric acid)
• P4O6 + H2O → H3PO3 (phosphorous acid)
• Hypophosphorous acid, H3PO2
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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) (sulfurous acid)
SO3(g) + H2O(l) → H2SO4(aq) (sulfuric acid)
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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 (strong acids)
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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
Notice the varying oxidation states of the halogen.
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Section 20.13
The Group 7A Elements
Halogen Oxyacids and Oxyanions
• 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 20.14
The Group 8A Elements
Noble Gases
• He and Ne form no compounds.
• Kr and Xe have been observed to form
chemical compounds:
Xe(g) + 2F2(g) → XeF4(s) [6 atm, 400oC]
XeF6(s) + 3H2O(l) → XeO3(aq) + 6HF(aq)
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Section 20.14
The Group 8A Elements
Of course there are more reaction types to consider
• Refer to Packet from Winter Break for more reaction
types
• (Ch 9, 10, 13 Chemical Equations Handouts)
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