Samacheer Kalvi 9th Science Solutions Chapter 12 Pdf
Tamilnadu Board Samacheer Kalvi 9th Science Solutions Chapter 12: Tamilnadu State Board Solution Class 9 Science Chapter 12 – PERIODIC CLASSIFICATION OF ELEMENTS.
Samacheer Kalvi 9th Science Solutions Chapter 12: Overview
| Board | Samacheer Kalvi |
| Class | 9 |
| Subject | Science |
| Chapter | 12 |
| Chapter Name | PERIODIC CLASSIFICATION OF ELEMENTS |
Samacheer Kalvi 9th Science Solutions Chapter 12 Pdf
Chapter 12
Periodic classification of elements
Choose the correct answer.
1) If Dobereiner is related with ‘law of triads’, then Newlands is related with
a) Modern periodic law
b) Hund’s rule
c) Law of octaves
d) Pauli’s Exclusion principle
Ans:c) Law of octaves
Because, law of Octaves was given by Newland.
2) Modern periodic law states that the physical and chemical properties of elements are the periodic functions of their
a) Atomic numbers
b) Atomic masses
c) Similarities
d) Anomalies
Ans: a) Atomic numbers
Because, according to Modern periodic the physical and chemical properties of elements are the periodic functions of their atomic numbers.
3) Elements in the modern periodic table are arranged in groups and periods.
a) 7, 18
b) 18, 7
c) 17, 8
d) 8, 17
Ans: a) 7, 18
Because, there are 7 periods and 18 groups in the modern periodic table.
Fill in the blanks.
1) In Dobereiner’s triads, the atomic weight of the middle element is—– the of the atomic masses of 1st and 3rd elements.
Ans: In Dobereiner’s triads, the atomic weight of the middle element is the nearly average of the atomic masses of 1st and 3rd elements.
2) Noble gases belong to group of the periodic table.
Ans: Noble gases belong to18 thgroup of the periodic table.
3) The basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was—
Ans: the basis of the classifications proposed by Dobereiner, Newlands and Mendeleev was atomic mass.
4) Example for liquid metal is—
Ans: Example for liquid metal is mercury.
III. Match the following.
Ans:
Triads: Dobereiner
Alkali metal: Sodium
Law of octaves: Newlands
Alkaline earth metal: Calcium
Modern Periodic Law: Henry Moseley
State whether true or false. If false, correct the statement.
1) Newlands’ periodic table is based on atomic masses of elements and modern periodic table is based on atomic number of elements.
Ans: True
2) Metals can gain electrons.
Ans: False
Because, metals have low ionization enthalpy due to which they can easily donates the valence electrons and acts as a reducing agent.
3) Alloys bear the characteristics of both metals and nonmetals.
Ans: True
4) Lanthanides and actinides are kept at the bottom of the periodic table because they resemble each other but they do not resemble with any other group elements.
Ans: True
5) Group 17 elements are named as Halogens.
Ans: True
Assertion and reason type questions.
Statement: Elements in a group generally possess similar properties but elements along a period have different properties.
Reason: The difference in electronic configuration makes the element differ in their chemical properties along a period.
a) Statement is true and reason explains the statement.
b) Statement is false but the reason is correct.
Ans: a) Statement is true and reason explains the statement.
Answer the following.
1) State modern periodic law.
Ans: The atomic number of an element indicates the no. of protons or no. of electrons in it. The physical and chemical properties of the element depends not only on the no. of protons in the nucleus but also on the no. of electrons and their arrangements around the nucleus. The modern periodic law states that, the Physical and chemical properties of the elements are the periodic functions of their atomic numbers. On the basis of modern periodic law, the modern periodic table is constructed.
2) What are groups and periods in the modern periodic table?
Ans: On the basis of modern periodic law the modern periodic table is constructed. According to it, all the elements are arranged in their increasing order of atomic no. The horizontal rows are called as periods. There are total 7 periods in modern periodic table. The elements are distributed in period on the basis of no. of shells in their atoms. The vertical columns starting from top to bottom in the periodic table are called as groups. There are total 18 groups in the periodic table. Based on the Physical and chemical properties of elements they are again classified into different families also.
3) What are the limitations of Mendeleev’s periodic table?
Ans: Russian chemist Dmitri Mendeleev observed that the elements of similar properties are repeated after equal interval when the elements are arranged in their increasing order of masses. And from this assumption he stated that, the Physical and chemical properties of the elements are the periodic functions of their atomic masses. There are some limitations of Mendeleev’s modern periodic table which are as follows: Elements having large difference in their properties are included in same group. For example: hard metals like Cu and Ag are placed with soft metals like Na and K in the same group. There is no proper position given to the element hydrogen. There non-metallic hydrogen was placed with the metals like Li, Na and K. The increasing order of mass was not followed strictly there.
For example: Co and Ni, Te and I.
There were no place or position for the isotopes in the periodic table.
4) State any five features of modern periodic table.
Ans: On the basis of modern periodic law the modern periodic table is constructed.
- According to it, all the elements are arranged in their increasing order of atomic no.
- The horizontal rows are called as periods. There are total 7 periods in modern periodic table.
- The elements are distributed in period on the basis of no. of shells in their atoms.
- The vertical columns starting from top to bottom in the periodic table are called as groups. There are total 18 groups in the periodic table.
- Based on the Physical and chemical properties of elements they are again classified into different families such as;
Group 1: alkali metals
Group 2: alkaline earth metals
Group 3-12: transition metals
Group 13: boron family
Group 14: carbon family
Group 15: nitrogen family
Group 16: oxygen family
Group 17: halogens
Group 18: Nobel gases
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