In this blog we discuss about the Mendeleeff’s Periodic Table
Periodic Classification of Elements
Many attempts were made to classify elements for study of their study.
Elements were divided on the basis of their states solid, liquid and gas and then by on the basis of Metals and non-metals but faced the failure due to the complex nature of the elements
Mendeleeff at last gave the shape of the periodic classification of the elements. He was able to find out the relation between the properties of the element with their atomic weight.
Nature of the Mendeleeff’s Periodic Table
When the elements are placed according to the increase of their atomic weight, it is found that elements in the same group possess the same properties.
In this fashion when elements are placed they are placed in the horizontal rows and vertical column.
The vertical column is known as group
The horizontal rows are known as period
Mendeleeff’s Periodic Table there are 9 groups including 0 group, which is started from
I, II, III, IV, V, VI, VII, VIII and 0
There are seven periods in the table. Elements in the group possess similar properties but elements in the same period have no similar properties. Each group is divided into two sub groups Sub group A and Sub group B
In Frist group A element are called alkali metals elements and second group B elements are called alkali earth element. Seventh group B elements are called halogens like Fl, Cl, Br, and I
0 group elements are called inert gases.
Periods and its number of elements
- First period is known as very short period containing only 2 elements H and He
- First short period containing 8 elements from Li to Ne
- Second short period containing 8 elements from Na to Ar
- Fourth periods is known as first long period containing 18 elements from K to Kr
- Fifth periods is known as second long period containing 18 elements from Rb to Xe
- Sixth period is known as first very long period containing 32 elements from Cs to Rn
- Seventh period is known as incomplete period containing 6 elements because
Lanthanide / rare earth elements: The 14 elements from Cerium (58) to Lutecium (71)
Actinide elements: The 14 elements from Thorium (90) to Lawrencium (103) all are radioactive
Transitional elements: The elements from Lanthanam (57) to Mercury (80)
Coinage metals: Copper, silver and gold
Mendeleff placed the elements according to their atomic weight. Nowadays atomic weight is replaced by atomic number. There are several advantages of using atomic number instead of atomic weight.
Mendeleff’s Periodic Law
It states that physical and chemical properties of elements and also their compounds are the periodic functions of their atomic number
- Systematic study of the properties of an element
- Correction of doubtful atomic weight
- Prediction of undiscovered elements
11Na = 2 + 8 + 1
The number of shell indicates the period
The number of electrons in the outer most shell indicate the group
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