Question

3. Define the modern periodic law. Discuss the construction of the long form of the periodic table​

Answer 1

Explanation:

The modern period ic law states that properties of elements are the periodic function of their atomic number.

in the long form of periodic table, there are 7 horizontal arrangements called periods and 18 vertical arrangements called groups.

Answer 2

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"If the elements are arranged in order of increasing atomic masses, their properties vary in definite manner from member to member of the series, but return more or less nearly to same value at certain fixed points in the series".

• The elements, if atranged according to their atomic weights exhibit an evident periodicity of properties.

• Elements which are similar as regards their chemical properties have atomic weights which either are of nearly same value , eg., Co, Ni or increase regularly, e,g, R, Rb, Ck.

• The arrangement of elements or groups of elements in the order of their atomic weights corresponds to their so called "valencies" as well as their distinctive properties.

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The modern periodic table consists of nine vertical columns called 'groups' and seven horizontal rows called 'periods'.

The groups are marked from I to VII.

First period., 2 elements , (Very short period)

Second period, 8 elements, (Short period)

Third period, 8 elements, (Short period)

Fourth period, 18 elements , (Long period)

Fifth period, 18 elements, (Long period)

Sixth period, 32 elements, (Very long period)

Seventh period, 6 elements, (Incomplete period)

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