NCERT Class 9th Science
Chapter 4
STRUCTURE OF THE ATOM

Page 43
Q.1     What are canal rays?
Q. 2 If an atom contains one electron and one proton, will it carry any charge or not?
Page 49
Q.1 On the basis of Thomson’s model of an atom, explain how the atom is neutral as a whole.
Q.2On the basis of Rutherford’s model of an atom, which subatomic particle is present in the nucleus of an atom?
Q.3 Draw a sketch of Bohr’s model of an atom with three shells.
Q.4 What do you think would be the observation if the α-particle scattering experiment is carried out using a foil of a metal other than gold?
Page 49
Q.1 Name the three sub-atomic particles of an atom.
Q.2 Helium atom has an atomic mass of 4 u and two protons in its nucleus. How many neutrons does it have?
Page 50
Q.1 Write the distribution of electrons in carbon and sodium atoms?
Q.2 If K and L shells of an atom are full, then what would be the total number of electrons in the atom?
Page 52
Q.1      How will you find the valency of chlorine, sulphur and magnesium?
Page 52
Q.1If number of electrons in an atom is 8 and number of protons is also 8, then
(i) what is the atomic number of the atom and
(ii) what is the charge on the atom?
Q.2With the help of Table 4.1, find out the mass number of oxygen and sulphur atom.
Page 53
Q.1 For the symbol H, D and T tabulate three sub - atomic particles found each of them.
Q.2 Write the electronic configuration of any pair of isotopes and isobars.
Exercise
Q.1 Compare the properties of electrons, protons and neutrons.
Q.2 What are the limitations of J.J. Thomson’s model of the atom?
Q.3: What are the limitations of Rutherford’s model of the atom?
Q.4 Describe Bohr’s model of the atom.
Q.5 Compare all the proposed models of an atom given in this chapter.
Q.6 Summarize the rules for writing of distribution of electrons in various shells for the first eighteen elements.
Q7: Define valency by taking examples of silicon and oxygen.
Q.8 Explain with examples
(i)   Atomic number,
(ii)Mass number,
(iii)Isotopes and
(iv)Isobars.
(v) Give any two uses of isotopes.
Q.9 Na⁺has completely filled K and L shells. Explain.
Q.10If bromine atom is available in the form of, say, two isotopes (49.7%) and (50.3%), calculate the average atomic mass of bromine atom.
Q. 11 The average atomic mass of a sample of an element X is 16.2 u. What are the percentages of isotopes and in the sample?
Q.12 If Z = 3, what would be the valency of the element? Also, name the element.
Q.13 Composition of the nuclei of two atomic species X and Y are given as under
                     X          Y
Protons      =         6        6
Neutrons   =          6        8
Give the mass numbers of X and Y. What is the relation between the two species?
Q.14 For the following statements, write T for ‘True’ and F for ‘False’.
Put tick (P ) against correct choice and cross ( O ) against wrong choice in the following question:
Q.15 Rutherford’s alpha-particle scattering experiment was responsible for the discovery of
(a)            the same physical properties
(b)            different chemical properties
(c)             different number of neutrons
(d)            different atomic numbers
Q.16: Isotopes of an element have
(a)             the same physical properties
(b)            different chemical properties
(c)             different number of neutrons
(d)            different atomic numbers
Q.17 Number of valence electrons in Cl⁻ ion are:
(a)            16
(b)            8
(c)             17
(d)            18
Q. 18 Which one of the following is a correct electronic configuration of sodium?
(a)            2, 8
(b)            8, 2, 1
(c)             2, 1, 8
(d)            2, 8, 1 Q.

Q.19 Complete the following Table