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## Chapter: 9th Science : Chemistry : Periodic Classification of Elements

Science : Chemistry : Periodic Classification of Elements : Book Back Important Questions, Answers, Solutions : Answer briefly, Answer in detail, Exercise Numerical Problems, Intext Activities

CHEMISTRY

PERIODIC CLASSIFICATION OF ELEMENTS

1. State modern periodic law.

Answer: “The Chemical and Physical properties of the elements are the periodic functions of their atomic number”.

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

(i) The horizontal rows in the periodic table are called periods.

(ii) Vertical columns in the periodic table starting from top to bottom are called groups.

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

(i) 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).

(ii) 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).

(iii) The increasing order of atomic mass was not strictly followed throughout. Eg.Co & Ni, Te & I

(iv) No place for isotopes in the periodic table.

4. State any five features of modern periodic table.

(i) All the elements are arranged in the increasing order of their atomic number.

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

(iii) The elements are placed in periods based on the number of shells in their atoms.

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

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

Intext Activities

ACTIVITY - 1

Find the pair of elements having similar properties by applying Newlands’ law of Octaves (Example: Mg & Ca):

Set I: F, Mg, C,O,B

Set II: A1, Si, S, CI, Ca

1. F- Cl

2. Mg –Ca

3. C- Si

4. O-S

5. B-Al

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