# CBSE Class 9 Science NCERT Solutions: Chapter 4, Structure of the Atom

May 22, 2018 13:07 IST
Class 9 Science NCERT Solution

NCERT books are very important for examination preparation as these books help in clearing out the theoretical concepts and strengthening the students’ foundation in the subject. This makes them able to tackle different types of questions easily.

NCERT books also offer a number of problems in the form of exercise questions for students to solve which helps them assess their understanding of the topics learned in the chapter. Solving these exercises in each chapter assures positive results as these questions are generally asked in exams directly or in twisted manner. Therefore, students who want to score well in their CBSE exams should practice NCERT questions.

Here we have collated the NCERT solutions for CBSE Class 9 Science Chapter 4- Structure of the Atom. Here, students can find a better approach to the questions given at the end of chapter- Structure of the Atom in NCERT textbook. All these solutions have been prepared by the subject experts and have been revised to bring accurate study material for our students.

Main topics discussed in Class 9 Science chapter- Structure of the Atom are:

• Charged Particles in Matter
• Structure of an atom
• Thomson’s model of an atom
• Rutherford’s model of an atom
• Bohr’s model of atom
• Neutrons
• Atomic valency
•  Atomic Number and Mass Number
• Isotopes
• Isobars

Some of the questions and their solution from NCERT Solutions for Class 9: Structure of the Atom, are as follows:

Q. What are canal rays?

Sol.

Canal rays or anode rays are the positively charged rays which are seen moving from the anode towards cathode in a specially designed discharge tube (with a porous cathode), when a high voltage is applied across the electrodes. These rays were discovered by Goldstein in 1886.

Q. On the basis of Thomson's model of an atom, explain how the atom is neutral as a whole?

Sol.

According to Thomson’s model of the atom, an atom consists of both negatively and positively charged particles. The negatively charged particles are embedded in the positively charged sphere These negative and positive charges are equal in magnitude. Thus, by counterbalancing each other's effect, they make an atom neutral.

Q. 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?

Sol.

If the α-particle scattering experiment is carried out using a foil of a metal other than gold, there would be no change in the observation. Rutherford used gold for α-particle scattering experiment because gold is the most malleable metal. More thick foils can be made by other metals like platinum. As the thickness of the foil increases, the possibility of correctness of the experiment decreases. So use of gold in this case is preferred.

Q. What are the limitations of JJ Thomson's model of the atom?

Sol.

Limitations of Thomson's model of atom are:

1. Thomson's model could not explain the experimental results of other scientists such as Rutherford, as there is no nucleus in the atomic model proposed by Thomson.

2. It does not have any experimental evidence in its support.

Q. What are the limitations of Rutherford's model of the atom?

Sol.

Limitations of Rutherford's model of an atom

1. The stability of the atom could not be explained. Because when a charged particle revolves in a circular orbit, it radiates energy continuously due to accelerated motion. This makes atom highly unstable. But we know that the atom is stable.

2. Rutherford's model could not explain the distribution of electrons in the extra nuclear portion of the atom.

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