Page 125 - Chemistry ICSE Class IX

Atomic Structure and Chemical Bonding 113
12. Compare the masses and charges of an electron, a proton and a neutron.

13. Where are the electrons, protons and neutrons located in an atom?
14. Write the number of valence electrons present in chlorine atom (atomic number 17).
15. (a) What is a proton? (b) How can it be produced?
16. Draw a labelled diagram for the alpha-particle scattering experiment.
17. How are the atomic number and mass number related to the number of protons and neutrons inside the nucleus
of an atom?
3+
18. The atomic numbers of Al and Cl are 13 and 17, respectively. What will be the number of electrons in Al and
–
Cl ? [Ans. 10, 18]
19. Two atoms of an element have the following nuclear compositions:
Atom : X Y
No. of protons : 17 17
No. of neutrons : 18 20
How are these two atoms related to each other?

20. Write the names and symbols of the three isotopes of hydrogen.
21. From the following nuclei:
(a) 8p + 8n (b) 8p + 9n
(c) 18p + 22n (d) 20p + 20n
Choose the isotopes. [Ans. Isotopes: (a) and (b)]

22. Write a short note on the electric discharge through gases under low pressure.
23. Describe a nucleus.
24. Compare the characteristics of electrons, protons and neutrons.
25. Write a short note on Böhr’s model of the atom.
2
26. What is 2n rule of Böhr and Bury? Draw diagrams to show the distribution of electrons in an atom of the
elements with the following atomic numbers: 7, 13 and 19.
27. How do atoms acquire stable noble gas con guration?
28. Fill in the blanks.
'NGEVTQPKE EQPſIWTCVKQP No. of
Mass Atomic No. of No. of No. of
number number protons electrons neutrons K L M N valence Designation
electrons
12 6 — — — — — — — — —
40 20 — — — — — — — — —

29. The de ection of the cathode rays by the electric and the magnetic elds was known before the well-known
experiments of J. J. Thomson. What was the main contribution of J. J. Thomson?
30. Describe the essential differences between cathode rays and the canal rays. Why are canal rays called so?
31. Describe the distribution of electrons in different shells of the following atoms: lithium, nitrogen, neon,
magnesium and silicon.
32. The atomic numbers of two elements A and B are 18 and 16, respectively. Which of the two should be chemically
more reactive?
33. Is there any relationship between the valency of an element and the number of electrons its atom has in its
outermost shell? Predict the valencies of helium (He), phosphorus (P), sulphur (S) and neon (Ne). The atomic
numbers of these elements are, 2, 15, 16 and 10, respectively.