Periodic
Table
Mandeleev’s
Periodic Table
Introduction
In 1969 a Russian chemist studied the
properties of elements, on the basis of experimental results, Mendeleev put
forwarded a law which is known as periodic law. The periodic law can be stated
as
The properties of the elements are
the periodic function of their atomic masses.
If the elements are arranged in order
to increase atomic masses then similar properties reoccur with definite
intervals. Mandeleev arrange the known elements in order to increase atomic
masses in the form of table, which is known as Mandeleev’s Table. In this
table, the elements with similar properties appear in the same vertical column
known as groups, the horizontal rows of the elements are called periods.
Advantages of Mandeleev’s Periodic Table
Mandeleev’s periodic table had a number
of advantages over the classification developed till that time.
1. Prediction of New Elements
While arranging the elements in order
to increase atomic masses in the table, Mandeleev come across certain positions
where no known element was seen fit to him. He left those spaces between vacant
and predicted that new elements would be discovered which could be fit in those
spaces.
2. Correction of Atomic Masses
At the time of Mandeleev the atomic
masses of some elements were not correctly known. Mandeleev’s classification of
elements help to correct the atomic masses of these elements.
3. Prediction About Properties
Mandeleev also made prediction about
the properties of the unknown elements. Many of these predictions were later
found correct. He was able to make these prediction because the elements
falling in the same group have similar properties.
4. Unication of Elements
Mandeleev’s classification co-relates
all the elements. The discovery of periodic classification showed that all the
elements despite their apparent diversity are co-related with one another and
make one systematic whole. Thus, all the elements are unified through a
classification.
Periods
There are seven periods (horizontal
rows) in the periodic table. The first table period contains two elements that
are hydrogen and helium. The second and third periods have eight elements
andeach are called short periods. The fourth and fifth periods have eighteen
elements each and are called long term. The sixth period contains thirty two elements
and is called very long period. The seventh period is incomplete. The
properties change gradually within the period or across the table from left to
right.
Groups
The vertical columns in the periodic
table are called groups or families. There are thirty-two groups or vertical
columns in the modern periodic table. There are light groups, which consist of
five or six elements and are called main groups, represented by ‘A’ group, to
distinguish them from remaining smaller groups by Transition Elements. The
elements of main groups are called Representative Elements or Typical Elements.
The remaining groups that are the
short groups of the periodic table are known as transition group. The elements
of these groups are collectively called transition elements. These elements are
further classified into outer transition elements and inner transition
elements. The elements of outer transition elements (d-block) are usually known
as ‘B’ group. The transition elements of ‘B’ group consist of eight groups and
three periods, which are known as a Series. The first series of outer
transition elements started from Sc (Scandium) to Zn (Zinc).
The inner transition elements
(f-block) consist of two series of elements having fourteen elements each. The
first series of inner transition elements is called Lanthanide series and the
elements are called Lanthanide’s. The second series of inner transition
elements is called Actinide series and the elements are called Actinides. The
Lanthanide and Actinide are also known as Rear Earth Elements and Heavy Rear
Earth Elements respectively.
Blocks of Periodic Table
On the basis of the kind of orbital
of elements occupied by the last electron, the periodic table is classified
into four blocks.
1. s – Block Elements
Those elements in which the last
electron occupies ‘s’ orbital are called s – block of the periodic table. The
elements of IA and IIA including hydrogen and helium are called s – Block
Elements.
2. p – Block Elements
Those elements in which the last
electron occupies ‘p’ orbital are called p – Block Elements of periodic table.
The elements of IIIA to VIIIA (six groups) are p – block elements.
3. d – Block Elements
Those elements in which last electron
occupies ‘d’ orbital are called d – Block Elements. The outer transition
elements that is B group (10 groups) belongs to d – block of Periodic Table.
4. f – Block Elements
Those elements in which last electron
occupies ‘f’ orbital are called f – Block Elements. The elements of inner
transition (14 groups) that is Lanthanide Series and Actinide Series belongs to
f – block elements.
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