Chapter 20. The Main Group Elements
20.1 Lewis Acids and Bases
20.2 Hard and Soft Lewis Acids and Bases
20.3 The Main Group Metals
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20.5 Phosphorus
20.4 The Metalloids
20.6 Other Nonmetals
20.1 Lewis Acids and Bases
Learning objective:
Explaining the chemistry of formation of adducts.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.1 Lewis Acids and Bases
 Works for solutions that are not aqueous.
 Focuses on electron pairs, instead of protons.
 Lewis Acid: any chemical species that acts as an
electron-pair acceptor: example B(CH3)3
 Lewis Base: any chemical species that acts as an
electron-pair donor: example NH3
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Adduct Formation
A +
Acid
:B → A – B
Base
Adduct
 Adduct: what is formed when a Lewis Acid and Base
react.
SiF4 + :F- → SiF5A
B Adduct
AlCl3 + :PCl3 → Cl3Al-PCl3
A
B
Adduct
 The chemical bond formed is called a coordinate
covalent bond.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Ammonia and Trimethylboron
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Recognizing Lewis Acids And Bases
Lewis acids can be:
1.
2.
3.
A molecule that has vacant valence orbitals.
A molecule with delocalized p bonds involving
oxygen.
A metal cation.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 20 – 1 Lewis Acids and Bases
Identify the Lewis acids and bases in each of the following
reactions and draw structures of the resulting
adducts:
a. AlCl3 + Cl- → AlCl4b. Co3+ + 6 NH3 → [Co(NH3)6]3+
c. SO2 + OH- → HSO3-
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.2 Hard and Soft Lewis Acids and Bases
Learning objective:
Applying the concepts of hardness and softness to
reactions.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.2 Hard and Soft Lewis Acids and Bases
 The strength with which an atom holds its valence
electrons determines the ability of that atom to act as a
Lewis Base.
 Polarizability – a
measure of how
tightly electrons
are bound to an
atom or molecule.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
The Hard-Soft Concept
 Hard Lewis Base – electron pairs of low polarizability
and high electronegativity. (e.g. F-)
 Soft Lewis Base – large donor atom of high
polarizability and low electronegativity. (e.g. I-)
 Hard Lewis Acid – acceptor atom with low
polarizability, most metal atoms and ions. The smaller
the ionic radius and the larger the charge, the harder
the acid. (e.g. Al3+)
 Soft Lewis Acid – relatively high polarizability, large
atoms with low oxidation state. (e.g. Hg2+)
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 20 – 2 Ranking Hardness and Softness
Rank the following groups of Lewis acids and bases from
softest to hardest: (a) H2S, H2O and H2Se (b) Fe, Fe3+
and Fe2+ (c) BCl3, GaCl3 and AlCl3
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
HSAB Principle
 HSAB = Hard – Soft – Acid – Base
 Hard Lewis acids tend to combine with hard Lewis
bases
 Soft Lewis acids tend to combine with soft Lewis bases.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
HSAB Principle
e.g. Soft acids such as gold and platinum have low
affinities for oxygen, a hard base. Thus these metals are
not easily oxidized.
e.g. Soft acids such as Pb, Hg, Ag have high affinities for
the soft base sulphur, and exist in nature as PbS, HgS
and Ag2S.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Metathesis Reactions
 Metathesis reaction – an exchange in bonding partners.
 Lewis acids and bases often undergo this exchange.
 They proceed in the direction that couples the harder
acid with the harder base.
 Important in organic synthesis because organoboron
and organoaluminum species are valuable reagents.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.3 The Main Group Metals
Learning objective:
Explaining the production, reactions, and uses of the
main group metals.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.3 The Main Group Metals
Although most metals if important are in the d block,
Al, Pb and Sn have considerable technological
importance.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Production of Aluminum
 The only main group element without filled d valence
orbitals is a hard Lewis acid
 Highly reactive, usually found in the +3 oxidation state,
difficult to reduce to Al atom.
 Al metal produced from the oxide by electrolysis.
 4.6 % of all electricity in Canada is used to produce Al
metal.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Production of Aluminum
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Uses of Aluminum
 Al alloys – aircraft bodies, trailers, cooking utensils, highway
signs, storage tanks, beverage cans, etc.
 AlCl3 – used as industrial catalysts, forms adduct with itself
(Al2Cl6)
 Catalysis of Friedel –
Crafts Reactions.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Sn and Pb
 +2 and +4 oxidation state common
 Easy to reduce to free metal
 Sn – alloys of bronze, solder and pewter, also used as
coating because of its resistant to oxidation
 Pb – most commonly used in automobile industry
(battery), being phased out of other process because of
the toxicity to organisms.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.4 The Metalloids
Learning objective:
Explaining the production, reactions, and uses of the
metalloids.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.4 The Metalloids
 B, Si, Ge, As, Sb and Te
 Si most abundant (27% of Earth’s crust)
 Si was not discovered until 1824, due mostly to the fact
that it was in the form of silica, SiO2.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Boron
 Has no valence d orbitals to participate in bonding.
 Boron trihalides are strong Lewis acids that react with a
wide collection of Lewis bases.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Silicon
 Primary ingredient in most
semiconductors, mainly in
the form of SiO2, silica.
 In order to make pure Si for
semiconductors, silica is first
converted to SiCl4, which is
then reduced to Si by Mg.
 Further purification is
achieved using zone refining.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Silicones
 Si is major component
of silicone polymers
 ~ 70,000 tons of
silicone polymers are
produced each year
 Used in greases,
caulking, gaskets,
biomedical devises,
cosmetics,
surfactants,
antifoaming agents,
hydraulic fluids and
water repellents.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.5 Phosphorous
Learning objective:
Explaining the production, reactions, and uses of
phosphorus.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.5 Phosphorous
 First extracted from human urine in 1669
 Occurs in deposits as apatite, Ca5(PO4)3X where X = F,
OH or Cl
 Elemental phosphorous: as P4 (white) it is highly
reactive, but linked it forms Red Phosphorous
 P4 with cross-linking: the result is black phosphorous
which is the most thermodynamically stable.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Example 20 – 3 Melting Points of Phosphorus
The melting point of white phosphorous is 44.1°C. In
contrast, red phosphorous remains a solid up to 400°C.
Account for this large difference in melting point.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Phosphoric Acid
 Ranks in top 10 of chemicals produced.
 345,000 tons produced per year in Canada
 Apatite is acidified with H2SO4 to form impure
phosphoric acid, which is used to make fertilizer.
H3PO4 + 2 NH3 → (NH4)2HPO4
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Phosphate Condensations
 Play an essential role in metabolism
ADP + H3PO4 → ATP + H2O
 ATP is a major biochemical energy source
 It releases energy in the reverse (hydrolysis) reaction.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.6 Other Nonmetals
Learning objective:
Explaining the production, reactions, and uses of the
other non-metals.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
20.6 Other Nonmetals
 Sulphur – sulphuric acid
dominates chemistry of
this element.
 Used in almost every
major chemical-related
industry
 H2SO4 – the least
expensive strong Brønsted
acid.
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Major Uses of Chlorine
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The Chlor-Alkali Process
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Standard Reduction Potentials for Cl Species
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Production of Fluorine
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 20 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 20 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 20 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 20 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 20 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.
Chapter 20 Visual Summary
Chemistry, 2nd Canadian Edition ©2013 John Wiley & Sons Canada, Ltd.