Science chapter 12

Answer the following.

 
1. State modern periodic law. 

The chemical and physical properties of 

the elements are the periodic functions of their 

atomic numbers.

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2. What are groups and periods in the modern periodic table? 

Periods:

The horizontal rows are called periods.There are seven periods in the periodic table.

Groups:

Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.

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3. What are the limitations of Mendeleev's periodic table? 

1.Elements with large difference in properties were included in the same group.

 Eg: Hard metals like copper (Cu) and silver (Ag) were included along with soft metals like sodium (Na) and potassium (K).

2.No proper position could be given to the element hydrogen. Non-metallic hydrogen was placed along with metals like lithium (Li), sodium (Na) and potassium (K).

3.The increasing order of atomic mass was not strictly followed throughout.

Eg. Co & Ni, Te & I.

4.No place for isotopes in the periodic table.

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4. State any five features of modern periodic table.

1.All the elements are arranged in the increasing order of their atomic number.

2.The horizontal rows are called periods.There are seven periods in the periodic 

table.

3.The elements are placed in periods based on the number of shells in their atoms.

4.Vertical columns in the periodic table starting from top to bottom are called groups. There are 18 groups in the periodic table.

5.Based on the physical and chemical properties of elements, they are grouped into various families

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