Periodic Table
2nd Year Chemistry Notes
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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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2nd Year Chemistry Notes