Thomson presented a model related to the structure of the atom which was like a christmas cake. According to him, the atom was a positively charged sphere in which electrons were like the dry fruits in a christmas cake. The example of watermelon can also be given.

On the basis of Thomson’s atomic model explain how the atom is neutral as a whole.

Complete the following table:

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

Number of valence electrons in Cl– ion are— (a) 16 (b) 8 (c) 17 (d) 18

Isotopes of an element have (a) the same physical properties (b) different chemical properties (c) different number of neutrons (d) different atomic numbers

Rutherford’s alpha particle scattering experiment was responsible for the discovery of. (a) Atomic (b) Electron (c) Proton (d) Neutron

For the following statements, write T for true and F for false.

Composition of the nuclei of two atomic species X and Y are given below : Give the mass number of X and Y. What is the relation between the two species ?

If Z = 3, What would be the valency of the element ? Also name the element.

Na+ has completely filled K and L shells. Explain.

Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

Compare all the proposed models of an atom given in this chapter.

What are the limitations of Rutherford’s model of the atom ?

Describe Bohr’s model of the atom.

What are the limitations of J.J. Thomson’s model of the atom?

Write the electronic configuration of any one pair of isotopes and isobar

For the Symbol H, D and T tabulate three sub-atomic particles found in each of them.

With the help of given find out the mass number of oxygen and sulphur atom.

If 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? (ii) What is the charge on the atom?

If the K and L shells of an atom are full, then what would be the total number of electrons in the atom?

If K and L shells of an atom are full, then what would be the total number of electrons in the atom?

Write the distribution of electrons in Carbon and Sodium atoms.

Helium atom has an atomic mass of 4u and two protons in its nucleus. How many neutrons does it have?

Name the three Sub-atomic particles of an atom.

What do you think would be the observation if the a-particle Scattering experiment is carried out using a foil of a metal other than gold?

Draw a Sketch of Bohr’s model of an atom with three shells.

On the basis Rutherford’s model of an atom, which sub-atomic particle is present in the nucleus of an atom?

What are canal rays?

Chapter 4 NCERT Class 9 Science SOLUTIONS

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