STRUCTURE OF ATOMS|CH#2 chemistry 9th|tutoronlines

Chapter No 2


Give short answer to the following Questions

Q.No.1. Write down two properties of cathode rays?

Ans. Cathode ray are negatively charged. They travel in straight lines perpendicular to the cathode surface.

Q.No.2. How does electron differ from neutron?

Ans. Electron has negative charge, while neutron has no charge. Electron revolves around the nucleus, while neutron is in the nucleus. The mass of electron is 1840 time smaller than that of neutron.

Q.No.3. State any two defects in Rutherford’s atomic model?

Ans. Following are the defects of this model.
(i) According to classical theory, electrons being charge particles should release or emit energy continuously and they should fall ultimately into nucleus.
(ii) If electron emit energy continuously, they should from a continuous spectrum, but infect line spectrum was observed.

Q.No.4. Who discovered neutron? Write its equation.

Ans. In 1932 Chadwick discovered neutron.

9Be4 + 4He2  → 12C6 + 1n0

Q.No.5. Write down the name of the particles which determine the mass of an atom?

Ans. Neutron and proton.

Q.No.6. Write two properties of neutron particles?

(i) It’s mass is equal to proton mass.
(ii) Neutron has no charge.

Q.No.7. Who discovered proton and when?

Ans. In 1886, gold stein discovered proton.

Q.No.8. Write two differences between Rutherford’s and bohr’s atomic theory?

Ans. Atomic theory of Rutherford’s and Atomic theory of Bohr’s are given bellow:

Sr. no Atomic theory of Rutherford’s Atomic theory of Bohr’s
1 It is based on classical theory. It is based on quantum theory.
2 Electrons revolves around nucleus. Electron revolves around nucleus in specific orbits.
Q.No.9. Find out the angular momentum of electron in the first orbit?

Ans. mv= nh/2π
= 6.63×10-34/ 6.28

Q.No.10. Why positive ray are called canal rays?

Ans. Goldstein observed the rays other than cathode rays in discharge tube. He observed that these rays move opposite to cathode rays. He used perforated cathode in discharge tube. These rays passed through this perforated cathode and produce light on tube wall. He give themas “Canal rays”.

Q.No.11. Write down any four properties of canal rays?

Ans. Properties of canal rays are given:

Sr. no Properties of canal rays
1 These rays travel in straight line opposite to cathode rays.
2 Their deflection in magnetic field shows that they have positive charge.
3 The nature of canal rays depend upon the nature of gas present in discharge tube.
4 The mass of these particles was found to be equal to proton or multiply of it.
Q.No.12. How positive rays are generated?

Ans. When cathode rays colloids with remaining gas molecules in discharge tube, the gas molecules converted into positive ions.

Q.No.13. What does Quantum mean?

Ans. Quantum mean specific energy. It is small amount of energy that can absorb or release in the from of electromagnetic radiation.

Q.No.14. What is plum pudding theory and who presented it?

Ans. Thomson present plum pudding theory according to him atoms are solid structures of positive charge, with tiny negative particles stuck inside. It is like plum in pudding.

Q.No.15. Write down the electronic configuration of Be and Ne.

Ans. Be =1S2, 2S2
Ne = 1S2, 2S2, 2P6

Q.No.16. Write down the electronic configuration of “S”?

Ans. 16S= 1S2, 2S2, 2P6, 3S2, 3P4

Q.No.17. How many sub shells are there in second shell?

Ans. There are two sub shells “s” and “p” in the second shell.

Q.No.18. Differentiate between shells and subshell?
Ans. Shell:

Electron revolves around the nucleus, according to their energy level, at different distances. These are called shells. These are represented by English letters K.L.M.N.

Sub shell:

The points of shell, where there is more chance of occurrences of electron are called sub shell or orbitals. These are represented by s, p, d and f.

Q.No.19. Write down the electronic configuration of (i) Na (ii) Al?


11Na= 1S2, 2S2, 2P6, 3S1

13Al = 1S2, 2S2, 2P6, 3S2, 3P1

Q.No.20. Write down electronic configuration of chlorine?

Ans. Cl = 1S2, 2S2, 2P6, 3S2, 3P5

Q.No.21. Write down electronic configuration of Nitrogen and Oxygen?


7N = 1S2, 2S2, 2P3

8O = 1S2, 2S2, 2P4

Q.No.22. How many electrons will be in M shell of an atom having atomic number 15.

Ans. There will be 5 electron.

Q.No.23. Define electronic configuration?

Ans. The arrangement of electron around the nucleus is called electronic configuration.

Q.No.24. Write down electronic configuration of Phosphorus ion and how many neutrons are in it?

Ans. 1531P3 = 1S2, 2S2, 2P6, 3S2, 3P6

It has 16 neutrons.

Q.No.25. Write down the number and name of sub shell in N shell?

Ans. The number of sub shell of N is 4, s, p, d and f.

Q.No.26. Write down the electronic configuration of nitrogen?

Ans. 1S2, 2S2, 2P3

Q.No.27. Write down the electronic configuration of Mg and Al?


Al+3 = 1S2, 2S2, 2P6

Mg+2 = 1S2, 2S2, 2P6

Q.No.28. Write down the electronic configuration of Oxygen?

Ans.8O = 1S2, 2S2, 2P4

Q.No.29. Write down the electronic configuration of silicon and Aluminium atoms?


14Si = 1S2, 2S2, 2P6, 3S2, 3P2

13Al = 1S2, 2S2, 2P6, 3S2, 3P1

Q.No.30. How many maximum electrons can be accommodated in L and M shells?

Ans. L shell has (8) eight, while M shell has eighteen (18) electrons.

Q.No.31. An element has 5 electrons in M shell. Find out its atomic number?

Ans. It’s atomic number is 15.

Q.No.32. Write down the electronic configuration of an element having 11 electrons?

Ans. 1S2, 2S2, 2P6, 3S1

Q. No.33. Write down the electronic configuration of Be and Ne?


Be = 1S2, 2S2

Ne = 1S2, 2S2, 2P6

Q.No.34. Define the term carbon dating?

Ans. The important method of age determination of old carbon containing objects is called carbon dating. It depend on measurement of radioactivity of C 14 present in the fossils.

Q.No.35. State any two use of isotope?
Ans. Radiotherapy:

Different isotopes like Sr 90 and p 32 of element are used for treatment of skin cancer.

Use in power generation:

Radioactive isotopes are used for production of electricity in nuclear reactor through controlled nuclear fission reaction.

Q.No.36. For what purpose U235 is used?

Ans. In nuclear reactor, slow moving neutrons are bombarded on uranium to generate electricity, for this purpose nuclear fission reaction is used.

Q.No.37. What is Nuclear fission reaction?

Ans. When slow moving neutrons are bombarded on nucleus, it is divided into two small nuclei with the emission of energy. This process is known as nuclear fission reaction.

Q.No.38. A patient has Goitre. How will it be detected?

Ans. To diagnose the goitre in thyroid gland, isotope of iodine is used as a tracer.

Q.No.39. Define Isotopes. give two example?

Ans. The atoms of element having same atomic number but different mass number are known as isotopes. e.g (i) The isotopes of carbon are 12C, 13C, 14C. (ii) Isotopes of chlorine 35Cl, 37Cl.

Q.No.40. Explain the isotopes of carbon?

Ans. The two isotopes of carbon 12C and 13C are stable, while 14C is radioactive. Naturally, the amount of 12C is 98.9%, while the amount of both 13C and 14C is 1.1%. They all have same number of electron and protons but different number of neutrons.

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