groups 3–12 See transition elements.
group 13 elements A group of elements in the *periodic table: boron
(B), aluminium (Al), gallium (Ga), indium (In), and thallium (Tl), which all
have outer electronic conÜgurations
ns
2 np
1 with no partly Ülled inner levels. They are the Ürst members of the
p-block. The group differs from the
alkali metals and alkaline-earth metals in displaying a considerable variation in properties as the group is
descended. Formerly, they were
classiÜed in group III, which consisted of two subgroups: group IIIB
(the main group) and group IIIA.
Group IIIA consisted of scandium
(Sc), yttrium (Yt), and lanthanum (La),
which are generally considered with
the *lanthanoids, and actinium (Ac),
which is classiÜed with the *actinoids. Scandium and yttrium now belong to group 3 (along with lutetium
and lawrencium).
Boron has a small atomic radius
and a relatively high ionization energy. In consequence its chemistry is
largely covalent and it is generally
classed as a metalloid. It forms a
large number of volatile hydrides,
some of which have the uncommon
bonding characteristic of *electrondeÜcient compounds. It also forms a
weakly acidic oxide. In some ways,
boron resembles silicon (see diagonal relationship).
As the group is descended, atomic
radii increase and ionization energies
are all lower than for boron. There is
an increase in polar interactions and
the formation of distinct M
3+ ions.
This increase in metallic character is
clearly illustrated by the increasing
basic character of the hydroxides:
boron hydroxide is acidic, aluminium
and gallium hydroxides are amphoteric, indium hydroxide is basic, and
thallium forms only the oxide. As the
elements of group 13 have a vacant
p-orbital they display many electronacceptor properties. For example,
many boron compounds form
adducts with donors such as ammonia and organic amines (acting as
Lewis acids). A large number of complexes of the type [BF 4 ]
–
, [AlCl 4 ]
– ,
[InCl 4 ]
– , [TlI 4 ]
– are known and the
heavier members can expand their
coordination numbers to six as in
[AlF 6 ]
3– and [TlCl 6 ]
3–
. This acceptor
property is also seen in bridged
dimers of the type Al 2 Cl 6 . Another
feature of group 13 is the increasing
stability of the monovalent state
down the group. The electron
conÜguration ns
2
np
1 suggests that
only one electron could be lost or
shared in forming compounds. In
fact, for the lighter members of the
group the energy required to promote an electron from the s-subshell
to a vacant p-subshell is small. It is
more than compensated for by the
resulting energy gain in forming
three bonds rather than one. This energy gain is less important for the
heavier members of the group. Thus,
aluminium forms compounds of the
type AlCl in the gas phase at high
temperatures. Gallium similarly
forms such compounds and
gallium(I) oxide (Ga 2 O) can be isolated. Indium has a number of
known indium(I) compounds (e.g.
InCl, In 2 O, In 3
I
[In
III Cl 6 ]). Thallium has
stable monovalent compounds. In
aqueous solution, thallium(I) compounds are more stable than the corresponding thallium(III) compounds.
See inert-pair effect.
group 14 elements A group of elements in the *periodic table: carbon
(C), silicon (Si), germanium (Ge), tin
(Sn), and lead (Pb), which all have
outer electronic conÜgurations ns
2
np
2
with no partly Ülled inner levels. Formerly, they were classiÜed in group
groups 3–12
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group 13 elements A group of elements in the *periodic table: boron
(B), aluminium (Al), gallium (Ga), indium (In), and thallium (Tl), which all
have outer electronic conÜgurations
ns
2 np
1 with no partly Ülled inner levels. They are the Ürst members of the
p-block. The group differs from the
alkali metals and alkaline-earth metals in displaying a considerable variation in properties as the group is
descended. Formerly, they were
classiÜed in group III, which consisted of two subgroups: group IIIB
(the main group) and group IIIA.
Group IIIA consisted of scandium
(Sc), yttrium (Yt), and lanthanum (La),
which are generally considered with
the *lanthanoids, and actinium (Ac),
which is classiÜed with the *actinoids. Scandium and yttrium now belong to group 3 (along with lutetium
and lawrencium).
Boron has a small atomic radius
and a relatively high ionization energy. In consequence its chemistry is
largely covalent and it is generally
classed as a metalloid. It forms a
large number of volatile hydrides,
some of which have the uncommon
bonding characteristic of *electrondeÜcient compounds. It also forms a
weakly acidic oxide. In some ways,
boron resembles silicon (see diagonal relationship).
As the group is descended, atomic
radii increase and ionization energies
are all lower than for boron. There is
an increase in polar interactions and
the formation of distinct M
3+ ions.
This increase in metallic character is
clearly illustrated by the increasing
basic character of the hydroxides:
boron hydroxide is acidic, aluminium
and gallium hydroxides are amphoteric, indium hydroxide is basic, and
thallium forms only the oxide. As the
elements of group 13 have a vacant
p-orbital they display many electronacceptor properties. For example,
many boron compounds form
adducts with donors such as ammonia and organic amines (acting as
Lewis acids). A large number of complexes of the type [BF 4 ]
–
, [AlCl 4 ]
– ,
[InCl 4 ]
– , [TlI 4 ]
– are known and the
heavier members can expand their
coordination numbers to six as in
[AlF 6 ]
3– and [TlCl 6 ]
3–
. This acceptor
property is also seen in bridged
dimers of the type Al 2 Cl 6 . Another
feature of group 13 is the increasing
stability of the monovalent state
down the group. The electron
conÜguration ns
2
np
1 suggests that
only one electron could be lost or
shared in forming compounds. In
fact, for the lighter members of the
group the energy required to promote an electron from the s-subshell
to a vacant p-subshell is small. It is
more than compensated for by the
resulting energy gain in forming
three bonds rather than one. This energy gain is less important for the
heavier members of the group. Thus,
aluminium forms compounds of the
type AlCl in the gas phase at high
temperatures. Gallium similarly
forms such compounds and
gallium(I) oxide (Ga 2 O) can be isolated. Indium has a number of
known indium(I) compounds (e.g.
InCl, In 2 O, In 3
I
[In
III Cl 6 ]). Thallium has
stable monovalent compounds. In
aqueous solution, thallium(I) compounds are more stable than the corresponding thallium(III) compounds.
See inert-pair effect.
group 14 elements A group of elements in the *periodic table: carbon
(C), silicon (Si), germanium (Ge), tin
(Sn), and lead (Pb), which all have
outer electronic conÜgurations ns
2
np
2
with no partly Ülled inner levels. Formerly, they were classiÜed in group
groups 3–12
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