How many chapters are there in the NCERT Solutions for Class 9 Science - PDF Flipbook

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STRUCTURE OF ATOM

SUMMARY –

➢ Discovery of electron, proton.
➢ Thompson’s model of atom.
➢ Rutherford’s model of atom and its defects.
➢ Discovery of neutron.
➢ Comparison of charge and mass of electron, proton and neutron.
➢ Bohr’s model of atom.
➢ Atomic number, mass number and electronic configuration.
➢ Valency, isotopes, isobars, isotones, isoelectronic.

SECTION – 1

1. Which of the following statement is true ?
A) A proton is 1837 times heavier than an electron.
B) A proton is 1/1837 times heavier than an electron.
C) A proton is 1837 times lighter than an electron.
D) Proton has the same mass as an electron.

2. A proton is usually represented as –

A) 1 P B) 1 H C) 4 He D) both A) and B)
1 1 2

3. When alpha particles are sent through a thin metal foil , most of them go straight through the foil
because –
A) Alpha particles are much heavier than electron.
B) Alpha particles are positively charged.
C) Most part of the atom is empty.
D) Alpha particles move with high velocity.

4. A neutron is represented as –

A) 0 n B) 1 n C) 1 n D) 1 n
0 1 0 −1

5. Many elements have non-integral masses because –
A) They have isobars.
B) Their isotopes have non-integral masses.
C) They have isotopes.
D) The constituents neutrons, protons and electrons combine to give fractional masses.

6. Two atoms of the same element are found to have different number of neutrons in their nuclei. These
two atoms are –

A) Isomers B) isotopes C) isobars D) allotropes

7. An atom which has a mass number of 14 and 8 neutrons is an –
A) isotope of oxygen B) isobar of oxygen C) isotope of carbon D) isobar of carbon

8. The mass of proton is –

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A) 1.00728amu B) 1.673 × 10-24gm C) 1.673 × 10-27 Kg D) All of these

SECTION -2

9. From what observation do you derive the following inferences ?
A) The most of the space inside the atom is empty.
B) The volume of the nucleus is very small.

10. Ar (40) and Ca (40) have the same mass number but their properties are entirely different. Why ?

11. Define atomic number. Why is it called the main characteristic property of the elements ?

12. Who proposed the existence of neutron and what was the basis of this assumption ?

13. What type of information is obtained about the atom by Rutherford particle scattering experiment ?

14. A) What are isotopes ? Give one example.

B) Give the application of isotopes in industry and in medicine

C) The relative mass of an element A is 16.2. There are two isotopes 16 A and 18 A of the element.
8 8

Calculate the percentage of these two isotopes present in the element.

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