1 to 18 (see Appendix). Horizontal
rows in the table are periods. The
Ürst three are called short periods;
the next four (which include transition elements) are long periods.
Within a period, the atoms of all the
elements have the same number of
shells, but with a steadily increasing
number of electrons in the outer
shell. The periodic table can also be
divided into four blocks depending
on the type of shell being Ülled: the
*s-block, the *p-block, the *d-block,
and the *f-block.
There are certain general features
of chemical behaviour shown in the
periodic table. In moving down a
group, there is an increase in metallic character because of the increased
size of the atom. In going across a period, there is a change from metallic
(electropositive) behaviour to nonmetallic (electronegative) because of
the increasing number of electrons
in the outer shell. Consequently,
metallic elements tend to be those
on the left and towards the bottom
of the table; nonmetallic elements
are towards the top and the right.
There is also a signiÜcant difference between the elements of the
second short period (lithium to
Ûuorine) and the other elements in
their respective groups. This is because the atoms in the second period
are smaller and their valence electrons are shielded by a small 1s
2
inner shell. Atoms in the other periods have inner s- and p-electrons
shielding the outer electrons from
the nucleus. Moreover, those in the
second period only have s- and porbitals available for bonding. Heavier atoms can also promote electrons
to vacant d-orbitals in their outer
shell and use these for bonding. See
also diagonal relationship; inertpair effect.
A
• The WebElements table produced by
Mark Winter at the University of
ShefÜeld
• Over 50 different forms of the periodic
table in the Chemogenesis web book by
Mark R. Leach
periplanar See torsion angle.
Perkin, Sir William Henry
(1838–1907) British chemist, who
while still a student accidentally produced mauvine, the Ürst aniline dye
and the Ürst dyestuff to be synthesized. Perkin built a factory to produce it, and made a fortune.
Permalloys A group of alloys of
high magnetic permeability consisting of iron and nickel (usually
40–80%) often with small amounts of
other elements (e.g. 3–5% molybdenum, copper, chromium, or tungsten). They are used in thin foils in
electronic transformers, for magnetic
shielding, and in computer memories.
permanent gas A gas, such as oxygen or nitrogen, that was formerly
thought to be impossible to liquefy.
A permanent gas is now regarded as
one that cannot be liqueÜed by pressure alone at normal temperatures
(i.e. a gas that has a critical temperature below room temperature).
permanent hardness See hardness of water.
permanganate See manganate(vii).
permonosulphuric(VI) acid See
peroxosulphuric(vi) acid.
Permutit Tradename for a *zeolite
used for water softening.
perovskite structure A type of
ionic crystal structure shown by compounds of the type ABO 3 . There is a
cubic arrangement with A atoms surrounded by 12 O atoms and B atoms
surrounded by 6 O atoms. Examples
periplanar
404
p
www.AzShimi.ir www.AzShimi.com
rows in the table are periods. The
Ürst three are called short periods;
the next four (which include transition elements) are long periods.
Within a period, the atoms of all the
elements have the same number of
shells, but with a steadily increasing
number of electrons in the outer
shell. The periodic table can also be
divided into four blocks depending
on the type of shell being Ülled: the
*s-block, the *p-block, the *d-block,
and the *f-block.
There are certain general features
of chemical behaviour shown in the
periodic table. In moving down a
group, there is an increase in metallic character because of the increased
size of the atom. In going across a period, there is a change from metallic
(electropositive) behaviour to nonmetallic (electronegative) because of
the increasing number of electrons
in the outer shell. Consequently,
metallic elements tend to be those
on the left and towards the bottom
of the table; nonmetallic elements
are towards the top and the right.
There is also a signiÜcant difference between the elements of the
second short period (lithium to
Ûuorine) and the other elements in
their respective groups. This is because the atoms in the second period
are smaller and their valence electrons are shielded by a small 1s
2
inner shell. Atoms in the other periods have inner s- and p-electrons
shielding the outer electrons from
the nucleus. Moreover, those in the
second period only have s- and porbitals available for bonding. Heavier atoms can also promote electrons
to vacant d-orbitals in their outer
shell and use these for bonding. See
also diagonal relationship; inertpair effect.
A
• The WebElements table produced by
Mark Winter at the University of
ShefÜeld
• Over 50 different forms of the periodic
table in the Chemogenesis web book by
Mark R. Leach
periplanar See torsion angle.
Perkin, Sir William Henry
(1838–1907) British chemist, who
while still a student accidentally produced mauvine, the Ürst aniline dye
and the Ürst dyestuff to be synthesized. Perkin built a factory to produce it, and made a fortune.
Permalloys A group of alloys of
high magnetic permeability consisting of iron and nickel (usually
40–80%) often with small amounts of
other elements (e.g. 3–5% molybdenum, copper, chromium, or tungsten). They are used in thin foils in
electronic transformers, for magnetic
shielding, and in computer memories.
permanent gas A gas, such as oxygen or nitrogen, that was formerly
thought to be impossible to liquefy.
A permanent gas is now regarded as
one that cannot be liqueÜed by pressure alone at normal temperatures
(i.e. a gas that has a critical temperature below room temperature).
permanent hardness See hardness of water.
permanganate See manganate(vii).
permonosulphuric(VI) acid See
peroxosulphuric(vi) acid.
Permutit Tradename for a *zeolite
used for water softening.
perovskite structure A type of
ionic crystal structure shown by compounds of the type ABO 3 . There is a
cubic arrangement with A atoms surrounded by 12 O atoms and B atoms
surrounded by 6 O atoms. Examples
periplanar
404
p
www.AzShimi.ir www.AzShimi.com