Class 9 Chemistry Chapter 2 Question Answer
Important Notes of Class 9 Chemistry Chapter 2 Question Answer Chapter No 2: Structure of Atom Class 9 English Medium written by Professor M. Shahid Suib. These notes are very helpful in the preparation of Class 9 Chemistry Chapter 2 Question Answer for students of the 9th class Chemistry English Medium and these are according to the paper patterns of all Punjab boards.
Summary and Contents:
Topics which are discussed in the notes are given below:
- Complete Exercise MCQs of Chapter No.2 Structure of Atom
- Complete Exercise Short Questions with Answers of Chapter No.2 Structure of Atom
- Give two characteristics of cathode rays. (Also A long Question).
- Write down any two properties of neutrons. (Also A long Question).
- Give two properties of positive rays. (Also A long Question).
- For what purpose U-235 is used?
- A patient has a goiter. How will it be detected? OR
For what purpose Iodine-131 is used?
- What are the defects of Rutherford’s atomic model?
- Write two observations of Rutherford's atomic model.
- Write down two postulates of Bohr’s atomic theory. (Also A long Question).
- Define the term carbon dating.
- Define electronic configuration.
OR
What is meant by electronic configuration?
- How many electrons are present in the K, L, M, and N shells of the atom?
- How many electrons are present in s, p, d, and f subshells of the atom?
- Write the electronic configuration of Hydrogen, boron, nitrogen, oxygen, sodium, aluminum,
Al3+ ion, Cl3+ ion, and phosphorus.
- Write down two isotopes of the following:
Hydrogen, Chlorine, Uranium Oxygen, and Carbon.
- Long Questions:
- Describe the result of the experiments of Rutherford.
- Write postulates of Bohr's atomic theory.
- Write down postulates of Bohr's atomic theory.
- Defects in Rutherford's Model: Although Rutherford's experiment proved that the 'plum-pudding' model of an atom was not correct, yet it had following defects:
- i. According to classical theory of radiation, electrons being the charged particles should release or emit energy continuously and they should ultimately fall into the nucleus.
- ii. If the electrons emit energy continuously, they should form a continuous spectrum but in fact, line spectrum was observed.
- Although the scientists had objections on the atomic model presented by Rutherford, yet it cultivated thought provoking ideas among them. They initiated the quest to answer the following questions:
- i. How can an atom collapse or why are atoms stable?
- ii. Why does an atom give line spectrum?
- Scientists considered there must be another model of atom. It indicated that Rutherford's model was not perfect.
- Bohr's Atomic Theory: Keeping in view the defects in Rutherford's Atomic Model, Neil Bohr presented another model of atom in 1913. The Quantum Theory of Max Planck was used as foundation for this model. According to Bohr's model, revolving electron in an atom does not absorb or emit energy continuously. The energy of a revolving electron is 'quantized' as it revolves only in orbits of fixed energy, called 'energy levels' by him. The Bohr's atomic model is shown in.
- The Bohr's atomic model was based upon the following postulates:
- 1. The hydrogen atom consists of a tiny nucleus and electrons are revolving in one of circular orbits of radius 'r' around the nucleus.
- ii. Each orbit has a fixed energy that is quantized.
- iii. As long as electron remains in a particular orbit, it does not radiate or absorb energy. The energy is emitted or absorbed only when an electron jumps from one orbit to another.
- IV. When an electron jumps from lower orbit to higher orbit, it absorbs energy and when it jumps from higher orbit to lower orbit it radiates energy. This change in energy, AE is given by following Planck's equation ΔΕ = Ε - Ε = hv Where, h is Planck's constant equal to 6.63 x 10 Js, and v is frequency of light.
- V. Electron can revolve only in orbits of a fixed angular moment mvr, given as: mvr = n h / 2π Where 'n' is the quantum number or orbit number having values 1,2,3 and so on.