Peridic Table

Periodic Classification of Elements

Q1)What is the need for classification of elements?
Ans)a)Classification helps to study elements better
    b)It correlates the properties of elements with some fundamental properties of all elements
    c)It reveals relationship between one and another element.

Q2)Describe the early attempts of classification.

Ans   a) Classification into metals and nonmetals—Elements were broadly divided into metals and nonmetals on the basis of a set of physical and chemical properties
    Reason for rejecting this classification---Only two major groups were formed elements which exhibited intermediate properties ( metalloids)were not taken care of.There was no justification for more reactive and less reactive elements.

    b)Classification on the basis of Dobereiner’s Triads—
J W Dobereiner attempted to classify elements in the form of triads
A triad is a group of three elements with similar physical and chemical properties arranged in increasing order of their atomic masses.

The law of traid states that atomic mass of the middle element of a triad is the arithmetic mean of the other two elements.

        Eg--- Tiad 1

|Elements             |Li                   |Na                 |K           |
|At mass             |7                   |23                 |39           |
|Average             | 7 + 39 = 46 /2 = 23                                 |

  Other examples are
              Chlorine (35.5) Bromine ( 80) Iodine (127)

Achievements of classification into triads---It highlighted the relationship between atomic masses and the properties of elements.

Drawbacks of this classification—Quite a large number of elements could not be grouped into triads and there was also a chance of grouping together dissimilar elements.

c) Classification on basis of Newlands law of octaves---New land arranged the elements in increasing order of atomic masses and found that elements with similar properties reoccurred each...