that contains a ring of atoms and is
aliphatic. Cyclohexane, C 6 H 12 , is an
example.
aliphatic compounds Organic
compounds that are *alkanes,
*alkenes, or *alkynes or their derivatives. The term is used to denote
compounds that do not have the special stability of *aromatic compounds. All noncyclic organic
compounds are aliphatic. Cyclic
aliphatic compounds are said to be
alicyclic.
alizarin An orange-red compound,
C 14 H 8 O 4 . The compound is a derivative of *anthraquinone, with hydroxyl groups substituted at the 1
and 2 positions. It is an important
dyestuff producing red or violet
*lakes with metal hydroxide.
Alizarin occurs naturally as the glucoside in madder. It can be synthesized by heating anthraquinone with
sodium hydroxide.
alkali A *base that dissolves in
water to give hydroxide ions.
alkali metals (group 1 elements)
The elements of group 1 (formerly
IA) of the *periodic table: lithium
(Li), sodium (Na), potassium (K),
rubidium (Rb), caesium (Cs), and
francium (Fr). All have a characteristic electron conÜguration that is a
noble gas structure with one outer
s-electron. They are typical metals (in
the chemical sense) and readily lose
their outer electron to form stable
M
+ ions with noble-gas conÜgurations. All are highly reactive, with
the reactivity (i.e. metallic character)
increasing down the group. There is
a decrease in ionization energy from
lithium (520 kJ mol
–1 ) to caesium
(380 kJ mol
–1
). The second ionization
energies are much higher and divalent ions are not formed. Other properties also change down the group.
Thus, there is an increase in atomic
and ionic radius, an increase in density, and a decrease in melting and
boiling point. The standard electrode
potentials are low and negative, although they do not show a regular
trend because they depend both on
ionization energy (which decreases
down the group) and the hydration
energy of the ions (which increases).
All the elements react with water
(lithium slowly; the others violently)
and tarnish rapidly in air. They can
all be made to react with chlorine,
bromine, sulphur, and hydrogen. The
hydroxides of the alkali metals are
strongly alkaline (hence the name)
and do not decompose on heating.
The salts are generally soluble. The
carbonates do not decompose on
heating, except at very high temperatures. The nitrates (except for
lithium) decompose to give the nitrite and oxygen:
2MNO 3 (s) → 2MNO 2 (s) + O 2 (g)
Lithium nitrate decomposes to the
oxide. In fact lithium shows a number of dissimilarities to the other
members of group 1 and in many
ways resembles magnesium (see diagonal relationship). In general, the
stability of salts of oxo acids increases down the group (i.e. with increasing size of the M
+ ion). This
trend occurs because the smaller
cations (at the top of the group) tend
to polarize the oxo anion more effectively than the larger cations at the
bottom of the group.
alkalimetry Volumetric analysis
using standard solutions of alkali to
determine the amount of acid present.
alkaline 1. Describing an alkali.
2. Describing a solution that has an
excess of hydroxide ions (i.e. a pH
greater than 7).
alkaline-earth metals (group 2
elements) The elements of group 2
aliphatic compounds
18
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aliphatic. Cyclohexane, C 6 H 12 , is an
example.
aliphatic compounds Organic
compounds that are *alkanes,
*alkenes, or *alkynes or their derivatives. The term is used to denote
compounds that do not have the special stability of *aromatic compounds. All noncyclic organic
compounds are aliphatic. Cyclic
aliphatic compounds are said to be
alicyclic.
alizarin An orange-red compound,
C 14 H 8 O 4 . The compound is a derivative of *anthraquinone, with hydroxyl groups substituted at the 1
and 2 positions. It is an important
dyestuff producing red or violet
*lakes with metal hydroxide.
Alizarin occurs naturally as the glucoside in madder. It can be synthesized by heating anthraquinone with
sodium hydroxide.
alkali A *base that dissolves in
water to give hydroxide ions.
alkali metals (group 1 elements)
The elements of group 1 (formerly
IA) of the *periodic table: lithium
(Li), sodium (Na), potassium (K),
rubidium (Rb), caesium (Cs), and
francium (Fr). All have a characteristic electron conÜguration that is a
noble gas structure with one outer
s-electron. They are typical metals (in
the chemical sense) and readily lose
their outer electron to form stable
M
+ ions with noble-gas conÜgurations. All are highly reactive, with
the reactivity (i.e. metallic character)
increasing down the group. There is
a decrease in ionization energy from
lithium (520 kJ mol
–1 ) to caesium
(380 kJ mol
–1
). The second ionization
energies are much higher and divalent ions are not formed. Other properties also change down the group.
Thus, there is an increase in atomic
and ionic radius, an increase in density, and a decrease in melting and
boiling point. The standard electrode
potentials are low and negative, although they do not show a regular
trend because they depend both on
ionization energy (which decreases
down the group) and the hydration
energy of the ions (which increases).
All the elements react with water
(lithium slowly; the others violently)
and tarnish rapidly in air. They can
all be made to react with chlorine,
bromine, sulphur, and hydrogen. The
hydroxides of the alkali metals are
strongly alkaline (hence the name)
and do not decompose on heating.
The salts are generally soluble. The
carbonates do not decompose on
heating, except at very high temperatures. The nitrates (except for
lithium) decompose to give the nitrite and oxygen:
2MNO 3 (s) → 2MNO 2 (s) + O 2 (g)
Lithium nitrate decomposes to the
oxide. In fact lithium shows a number of dissimilarities to the other
members of group 1 and in many
ways resembles magnesium (see diagonal relationship). In general, the
stability of salts of oxo acids increases down the group (i.e. with increasing size of the M
+ ion). This
trend occurs because the smaller
cations (at the top of the group) tend
to polarize the oxo anion more effectively than the larger cations at the
bottom of the group.
alkalimetry Volumetric analysis
using standard solutions of alkali to
determine the amount of acid present.
alkaline 1. Describing an alkali.
2. Describing a solution that has an
excess of hydroxide ions (i.e. a pH
greater than 7).
alkaline-earth metals (group 2
elements) The elements of group 2
aliphatic compounds
18
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