Periodic Table
Introduction
In the early nineteenth century only 30 elements were known and were classified into three
types on the basis of their physical properties as: metals, nonmetals and metalloids.
In 1869, Russian cemist Dmitri Mendeleev put forth periodic table of the 63 elements known
at that time using the atomic mass and properties of elements. Mendeleev’s periodic table
was based on the Mendeleev’s periodic law which is stated as:
“The physical and chemical properties of elements are periodic function of their atomic
masses.”
Mendeleev arranged the elements known at that time in increasing order of their atomic masses.
The serial or ordinal number of an element in the increasing order of atomic mass referred to
as its atomic number. He folded this list in accordance with recurrence of properties of
elements and formed his periodic table consisting of vertical groups and horizontal series
(now called periods).
After the discovery of atomic structure, the atomic number, which was an ordinal number
assigned to element in Mendeleev periodic table, was recognized as the proton number (Z)
of the element. This was outcome of Henry Moseley’s work (1913) on x-ray spectroscopic
study of large number of elements. Moseley showed that the frequency of x-ray emitted by an
element is related to its atomic number Z, rather than the atomic mass. The atomic number, Z,
was considered as more fundamental property of the atom than the atomic mass. As a result,
Mendeleev’s periodic law was modified. It is called the modern periodic law and is stated as:
“The physical and chemical properties of elements are periodic function of their atomic
numbers.”
Structure of the Modern Periodic Table
Over a long period of time many scientists have come up with different forms of periodic table.
However, the so-called ‘long form periodic table’ or ‘the modern periodic table’, which is
a revised version of Mendeleev’s periodic table, is the most convenient and widely used form
of the periodic table of elements today.
The modern periodic table has horizontal rows intersecting the vertical columns giving rise
to a number of boxes. The horizontal rows are called periods (which Mendeleev called series)
and the vertical columns are called groups. There are seven periods (numbered 1 to 7) and
eighteen groups (numbered 1 to 18) in the modern periodic table.
There are in all 118 boxes to accommodate 118 elements in the modern periodic table. On
today all the 118 boxes are filled as a result of discovery of manmade elements. IUPAC has
approved names and symbols of all the 118 elements.
, The overall shape of the modern periodic table shows that it is divided into four blocks. Two
groups on the left constitute the s-block, six groups on the right constitute the p-block, ten
groups in the center form the d-block and the two series at the bottom constitute the f-block.
Electronic configuration in the four blocks
s-Block
The general outer electronic configuration of s-block elements is ns1-2. Thus elements of the
group-1 and group-2 belong to the s-block. The s-block is present on the left extreme of the
modern periodic table.
p-Block
The p-block elements have the general outer electronic configuration ns² np1-6. Some variations
are present due to half-filled and fully-filled subshell stability.
Example:
For carbon (Z = 6), its outer electronic configuration is 2s² 2p². This is because both 2s and 2p
subshells are half-filled.
d-Block
The last electron in the d-block elements is filled in a d-subshell. A d-subshell is present along
with an s-subshell of the outermost shell. Thus the general outer electronic configuration is
(n−1)d¹–¹⁰ ns¹–².
The d-block elements are also called transition elements.
f-Block
In the f-block elements the last electron is filled in an f-orbital. As there are seven orbitals in
an f-subshell, the general outer electronic configuration of the f-block is
ns² (n−1)d⁰–¹ (n−2)f¹–¹⁴.
The stability of half-filled and fully-filled subshells needs to be accounted for.
There are 14 f-block elements called the lanthanoids and actinoids, put one below the other.
The f-block is placed separately at the bottom of the periodic table.
Introduction
In the early nineteenth century only 30 elements were known and were classified into three
types on the basis of their physical properties as: metals, nonmetals and metalloids.
In 1869, Russian cemist Dmitri Mendeleev put forth periodic table of the 63 elements known
at that time using the atomic mass and properties of elements. Mendeleev’s periodic table
was based on the Mendeleev’s periodic law which is stated as:
“The physical and chemical properties of elements are periodic function of their atomic
masses.”
Mendeleev arranged the elements known at that time in increasing order of their atomic masses.
The serial or ordinal number of an element in the increasing order of atomic mass referred to
as its atomic number. He folded this list in accordance with recurrence of properties of
elements and formed his periodic table consisting of vertical groups and horizontal series
(now called periods).
After the discovery of atomic structure, the atomic number, which was an ordinal number
assigned to element in Mendeleev periodic table, was recognized as the proton number (Z)
of the element. This was outcome of Henry Moseley’s work (1913) on x-ray spectroscopic
study of large number of elements. Moseley showed that the frequency of x-ray emitted by an
element is related to its atomic number Z, rather than the atomic mass. The atomic number, Z,
was considered as more fundamental property of the atom than the atomic mass. As a result,
Mendeleev’s periodic law was modified. It is called the modern periodic law and is stated as:
“The physical and chemical properties of elements are periodic function of their atomic
numbers.”
Structure of the Modern Periodic Table
Over a long period of time many scientists have come up with different forms of periodic table.
However, the so-called ‘long form periodic table’ or ‘the modern periodic table’, which is
a revised version of Mendeleev’s periodic table, is the most convenient and widely used form
of the periodic table of elements today.
The modern periodic table has horizontal rows intersecting the vertical columns giving rise
to a number of boxes. The horizontal rows are called periods (which Mendeleev called series)
and the vertical columns are called groups. There are seven periods (numbered 1 to 7) and
eighteen groups (numbered 1 to 18) in the modern periodic table.
There are in all 118 boxes to accommodate 118 elements in the modern periodic table. On
today all the 118 boxes are filled as a result of discovery of manmade elements. IUPAC has
approved names and symbols of all the 118 elements.
, The overall shape of the modern periodic table shows that it is divided into four blocks. Two
groups on the left constitute the s-block, six groups on the right constitute the p-block, ten
groups in the center form the d-block and the two series at the bottom constitute the f-block.
Electronic configuration in the four blocks
s-Block
The general outer electronic configuration of s-block elements is ns1-2. Thus elements of the
group-1 and group-2 belong to the s-block. The s-block is present on the left extreme of the
modern periodic table.
p-Block
The p-block elements have the general outer electronic configuration ns² np1-6. Some variations
are present due to half-filled and fully-filled subshell stability.
Example:
For carbon (Z = 6), its outer electronic configuration is 2s² 2p². This is because both 2s and 2p
subshells are half-filled.
d-Block
The last electron in the d-block elements is filled in a d-subshell. A d-subshell is present along
with an s-subshell of the outermost shell. Thus the general outer electronic configuration is
(n−1)d¹–¹⁰ ns¹–².
The d-block elements are also called transition elements.
f-Block
In the f-block elements the last electron is filled in an f-orbital. As there are seven orbitals in
an f-subshell, the general outer electronic configuration of the f-block is
ns² (n−1)d⁰–¹ (n−2)f¹–¹⁴.
The stability of half-filled and fully-filled subshells needs to be accounted for.
There are 14 f-block elements called the lanthanoids and actinoids, put one below the other.
The f-block is placed separately at the bottom of the periodic table.
