22:
Chemistry Chapter of the
Main-Group Metals
1
General Observations
Several general observations can be made
about the main-group elements.
First, the metallic characteristics of these
elements generally decrease across a period
from left to right in the periodic table.
Second, metallic characteristics of the maingroup elements become more pronounced
going down any column (group).
2
General Observations
Several general observations can be made
about the main-group elements.
Finally, a second-period element is
usually rather different from the other
elements in its group.
Table 21.1 summarizes the properties of
metallic and nonmetallic elements.
3
Group IA: The Alkali Metals
The Group IA metals (alkali metals) are
soft (Figure 21.10), chemically reactive
elements.
The alkali metals usually react by losing an
electron to become +1 cations.
Because of their reactivity, they never
occur as free metals in nature.
They do occur extensively in silicate
minerals.
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Group IA: The Alkali Metals
The Group IA metals (alkali metals) are
soft (Figure 22.3), chemically reactive
elements.
Lithium, sodium, and potassium are
industrially important alkali metals.
In recent years, the commercial uses of
lithium (usually obtained from the chloride)
include its use in the production of lowdensity alloys and as a battery anode.
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Group IA: The Alkali Metals
Lithium
Lithium, like other alkali metals reacts with
water to produce lithium hydroxide and H2.
Lithium burns in air to produce lithium
oxide, Li2O, a white powder.
LiNH2 is used in the preparation of
antihistamines.
LiH is used as a reducing agent in organic
synthesis.
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Group IA: The Alkali Metals
Sodium
Sodium metal is prepared in large
quantities.
It is used as a reducing agent in the
preparation of other metals, such as
titanium and zirconium, and in the
preparation of dyes and pharmaceuticals.
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Group IA: The Alkali Metals
Sodium
Sodium hydroxide is prepared by the
electrolysis of aqueous sodium chloride;
as a strong base, it has many useful
commercial applications, including
aluminum production and petroleum
refining.
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Group IA: The Alkali Metals
Sodium
Sodium carbonate is obtained from the mineral
trona, which contains sodium carbonate and
sodium hydrogen carbonate, and by the Solvay
process from salt (NaCl) and limestone (CaCO3).
Sodium carbonate is used to make glass.
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Group IA: The Alkali Metals
Potassium
Potassium metal is produced in relatively small
quantities, but potassium compounds are
important.
Large quantities of potassium chloride are used as
a plant fertilizer.
Table 21.3 summarizes the major uses of the
alkali metal compounds.
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Group IIA: The Alkaline Earth
Metals
Magnesium and calcium are the most
important of the Group IIA (alkaline earth)
metals.
Magnesium and its alloys are important
structural metals.
Calcium is important primarily as its
compounds, which are prepared from
natural carbonates, such as limestone, and
the sulfates, such as gypsum.
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Group IIA: The Alkaline Earth
Metals
Magnesium and calcium are the most
important of the Group IIA (alkaline earth)
metals.
When limestone is heated strongly, it decomposes
to calcium oxide (lime).
Enormous quantities of lime are used in the
production of iron from its ores.
Table 21.4 summarizes the major uses of the
alkaline earth compounds.
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Group IIIA and Group IVA
Metals
Of the Group IIIA and Group IVA metals,
aluminum, tin, and lead are especially
important.
Aluminum is the third most abundant element in
the earths crust.
It is obtained commercially from bauxite; through
chemical processing bauxite yields pure aluminum
oxide.
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Group IIIA and Group IVA
Metals
Aluminum
Most of this aluminum oxide is used in the
production of aluminum by electrolysis.
Some aluminum oxide is used as a carrier for
heterogeneous catalysts and in manufacturing
industrial ceramic materials.
Table 21.5 lists some uses of aluminum
compounds.
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Group IIIA and Group IVA
Metals
Tin
Tin is normally a metal (called white tin) but does
undergo a low-temperature conversion to a
nonmetallic form (called gray tin).
Tin is obtained by reduction of cassiterite, a
mineral form of SnO2.
Tin is used to make tin plate, bronze, and solder.
15
Group IIIA and Group IVA
Metals
Lead
Lead is obtained from galena, which is a sulfide
ore, PbS.
More than half of the lead produced is used to
make electrodes for lead storage batteries.
Litharge, or lead(II) oxide, is an important lead
compound from which other lead compounds are
prepared.
Table 21.6 lists uses of tin and lead compounds.
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Chemistry of the Nonmetals
The nonmetals do not exhibit metallic
properties in their elemental form, with
nearly half of them being colorless gases.
In the next sections we will look at the
chemical and physical properties of the
most important nonmetals.
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Hydrogen
Hydrogen is the most abundant element in
the universe and is the third most abundant
element of the surface of the earth.
Most of the hydrogen on earth is found in
water.
Hydrogen has three isotopes: protium,
deuterium, and tritium.
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Hydrogen
Hydrogen
Protium is the most abundant, with less that
0.02% being deuterium and only a trace being
radioactive tritium.
Deuterium and tritium isotopes can be
substituted for protium in chemical compounds in
order to provide markers that can be followed
during a chemical reaction, or to change the
physical properties of the compound.
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Hydrogen
Hydrogen
Elemental hydrogen is produced on an industrial
scale by the steam-reforming process in which a
hydrocarbon is reacted with water in the presence
of a catalyst at high temperature.
The bulk of the hydrogen produced in this manner
is used to make organic compounds including
methanol.
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Hydrogen
Hydrogen
Hydrogen forms three classes of binary
compounds called binary hydrides: ionic
hydrides, covalent hydrides, and metallic
hydrides.
ionic The hydrides are reactive solids formed either
by the reaction of hydrogen with an alkali metal to
form compounds with the formula MH, or with larger
alkaline earth metals to form MH2.
The covalent hydrides are compounds in which
hydrogen is covalently bonded to another element.
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Hydrogen
Hydrogen
The metallic hydrides contain a transition metal
element and hydrogen.
In these compounds, the lattice of metal atoms
forms a porous structure that allows hydrogen
atoms to enter and bond.
Metallic hydrides are often nonstoichiometric,
meaning that the ratio of hydrogen atoms to metal
atoms is not a whole number.
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Group IVA: The Carbon Family
Carbon is the least metallic of the Group
IVA elements.
Catenation is an important feature of carbon
chemistry and is responsible for the enormous
number of organic compounds.
Carbon has several allotropes, the principal ones
being diamond and graphite, which are covalentnetwork solids, and buckminsterfullerene, which is
molecular (C60).
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Group IVA: The Carbon Family
Carbon
The element has important industrial uses,
including carbon black for rubber tires.
The principal oxides of carbon are CO and CO2.
Mixtures of carbon monoxide and hydrogen are
used to prepare various organic compounds.
Liquid and solid carbon dioxide are used as
refrigerants, and the gas is used to make
carbonated beverages.
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Group IVA: The Carbon Family
Silicon is the second most abundant
element in the crust of the earth.
The majority of silicon-containing compounds consist
of chains and networks of silicon-oxygen bonds.
Sharing some of the structural attributes of the
network solids discussed in Chapter 11 are the
silicones; materials that contain chains or rings of
SiO bonds with organic groups bonded to the
silicon atoms.
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Group IVA: The Carbon Family
Silicon
By varying the bonding between the rings or chains, the
silicones can be made to be oils, elastomers, or resins.
Due to their low reactivity and thermal stability, silicones
find applications ranging from cosmetics to hydraulic fluids.
The silicon hydrides (also known as silanes) and silicon
halides are silicon-containing compounds that do not contain
SiO bonds.
The silanes consist of straight chains or branched chains
of silicon atoms combined with hydrogen atoms with the
general formula SinHn+2 or as rings with the formula Si5H10
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or Si6H12.
Group VA: Nitrogen and the
Phosphorus Family
Of the Group VA elements, nitrogen and
phosphorus are particularly important.
Nitrogen, N2, is obtained from liquid air by
fractional distillation; liquid nitrogen is used as a
refrigerant.
Ammonia, NH3, is the most important compound
of nitrogen. It is prepared from the elements and is
used as a fertilizer.
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Group VA: Nitrogen and the
Phosphorus Family
Nitrogen
Ammonia is also the starting compound for the
manufacture of other nitrogen compounds.
For example, in the Ostwald process for the
preparation of nitric acid, ammonia is burned in
the presence of a catalyst to nitric oxide, NO.
The nitric oxide reacts with oxygen to give nitrogen
dioxide, which reacts with water to give nitric
acid.
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Group VA: Nitrogen and the
Phosphorus Family
Phosphorus
Phosphorus has two common allotropes, white
phosphorus (P4) and red phosphorus (chain
structure).
White phosphorus is obtained by heating a
phosphate mineral with sand and coke in an
electric furnace.
When phosphorus burns in air, it forms
phosphorus(V) oxide, P4O10.
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Group VA: Nitrogen and the
Phosphorus Family
Phosphorus
This oxide reacts with water to give
orthophosphoric acid, H3PO4.
Phosphorus has many oxoacids; most are
obtained by condensation reactions with
orthophosphoric acid.
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Group VA: Nitrogen and the
Phosphorus Family
Phosphorus
One series is called the polyphosphoric acids;
they have the general formula Hn+2PnO3n+1.
Triphosphoric acid is an example; sodium
triphosphate, Na5P3O10, is used in detergents.
The metaphosphoric acids have the general
formula (HPO3)n.
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Group VIA: Oxygen and the
Sulfur Family
Oxygen, a Group VIA element, occurs in
the atmosphere (as O2), but mostly it is
present on earth as oxide and oxoanion
minerals.
Oxygen has two allotropes: dioxygen, O2, and
ozone, O3.
Dioxygen, usually called simply oxygen, is obtained
commercially from liquid air.
Oxygen reacts with almost all elements to give
oxides or in some cases, peroxides or super-oxides.
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Group VIA: Oxygen and the
Sulfur Family
Sulfur, another Group VIA element, occurs
in sulfate and sulfide minerals.
Free sulfur, S8 , occurring in deep under-ground
deposits is mined by the Frasch process.
Sulfur is also produced by the Claus process, in
which hydrogen sulfide (obtained from natural gas
and petroleum) is partially burned.
Most of the sulfur is used to prepare sulfuric acid
by the contact process.
In this process, sulfur is burned to sulfur dioxide,
SO2, which in the presence of a catalyst and
oxygen forms sulfur trioxide, SO3.
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Group VIA: Oxygen and the
Sulfur Family
Sulfur
This oxide dissolves in concentrated sulfuric acid,
which when diluted with water gives additional
sulfuric acid.
Sulfuric acid is the most important compound of
sulfur.
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Group VIIA: The Halogens
The Group VIIA elements, or halogens, are
reactive.
Chlorine (Cl2), a pale greenish-yellow gas, is
prepared commercially by the electrolysis of
aqueous sodium chloride.
Its principal uses are in the preparation of
chlorinated hydrocarbons and as a bleaching
agent and disinfectant.
Hydrogen chloride, HCl, is one of the most
important compounds of chlorine; aqueous
solutions of HCl are known as hydrochloric acid.
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Group VIIIA: The Noble Gases
The Group VIIIA elements, the noble
gases, were discovered at the end of the
nineteenth century.
Although the noble gases were at first thought to
be unreactive, compounds of xenon, krypton,
radon, and argon are now known.
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