Atomic Structure and Chemical Bonding Exe-4A Chemistry Class-9 ICSE Selina Publishers

Atomic Structure and Chemical Bonding Exe-4A Chemistry Class-9 ICSE Selina Publishers Solutions Chapter-4. Step By Step ICSE Selina Concise Solutions of Chapter-4 Atomic Structure and Chemical Bonding with All Exercise including MCQs, Very Short Answer Type, Short Answer Type, Long Answer Type, Numerical and Structured/Application Questions Solved . Visit official Website CISCE for detail information about ICSE Board Class-9.

Atomic Structure and Chemical Bonding Exe-4A Chemistry Class-9 ICSE Concise Selina Publishers

Board ICSE
Publications Selina Publication
Subject Chemistry
Class 9th
Chapter-4 Atomic Structure and Chemical Bonding
Book Name Concise
Topics Solution of Exercise – 4A 
Academic Session 2023-2024

A. Exercise – 4A

Atomic Structure and Chemical Bonding Class-9 Chemistry Concise Solutions  

Page-62

Question 1.

What is the contribution of the following in atomic structure?

(a) Maharshi Kanada

(b) Democritus

Answer:

(a) According to Maharshi Kanada:

(i) Matter consisted of indestructible particles called paramanus (now called atoms).

(ii) A paramanu does not exist in the free state, rather it combines with other paramanus to form a bigger particle called the anu (now called a molecule).

(b) Democritus called paramanu as atom which comes from the Greek word atoms, meaning indivisible.

Question 2.

State Dalton’s atomic theory.

Answer:

Main postulates of Dalton’s atomic theory:

(i) Matter consists of very small and indivisible particles called atoms.

(ii) Atoms can neither be created nor be destroyed.

(iii) The atoms of an element are alike in all respects, but they differ from the atoms of other elements.

(iv) Atoms of an element combine in small numbers to form molecules.

(v) Atoms of one element combine with atoms of another element in a simple ratio to form molecules of compounds.

(vi) Atoms are the smallest units of matter which can take part in a chemical reaction.

Question 3.

What is an α (alpha) particle?

Answer:

An α-particle is a doubly charged helium ion (He2+) containing two protons and two neutrons. It is formed by removing two electrons from the helium atom.

Question 4.

What are cathode rays? How are these rays formed?

Answer:

Cathode rays are the beam of electrons which travel from the negatively charged end (i.e. cathode to anode) of a vacuum tube, across a voltage difference between the electrodes placed at each end.

Formation of cathode rays:`

Generally gases are poor conductors of electricity. However, when a high voltage charge from an induction coil is applied to tubes filled with gases at very low pressure (0.01 mm of mercury), the gases become good conductors of electricity and begin to flow in the form of rays.

These rays are called cathode rays and they travel from the cathode towards the anode.

production of cathode rays

Question 5.

What is the nature of the charge on

(i) Cathode rays and

(ii) Anode rays?

Answer:

(i) Cathode rays are negatively charged as they consist of negatively charged particles called electrons.

(ii) Anode rays are made of positively charged particles.

Question 6.

How are X-rays produced?

Answer:

When a beam of cathode rays is made to fall upon hard metallic targets like tungsten, X-rays are produced.

Question 7.

Why are anode rays also called as ‘canal rays’?

Answer:

When perforated rays were used in the discharge tube, another set of rays travelling in a direction opposite to that of the cathode rays, i.e. from the anode towards the cathode, is seen, as in the figure below. These rays are called canal rays because they passed through the holes or canals in the cathode. These rays were named positive rays or anode rays.

production of anode rays

Question 8.

How does cathode ray differ from as anode rays?

Answer:

Cathode rays Anode rays
These rays travel from the cathode to the anode. These rays travel from the anode to the cathode.
They are made of negatively charged particles. They are made of positively charged particles.
They produce a greenish yellow fluorescence on a soda-glass screen. They produce fluorescence on a zinc sulphide screen.
They are affected by an electric field, i.e. they are inflected towards a positive field and deflected towards a negative field. They are deflected by electric and magnetic fields but in a direction opposite to that of cathode rays.

 

Question 9.

State one observation which shows that atom is not indivisible.

Answer:

Chadwick discovered neutral particles present in an atom by bombarding light nuclei like beryllium with alpha particles, i.e. helium nuclei.

4Be9 + 2He4  → 6C12 + 0n1

Discovery of the neutron also showed that an atom is divisible.

Question 10.

(a) Name an element which does not contain neutron

(b) If an atom contains one electron and one proton, will it carry as a whole is neutral

Answer:

(a) Hydrogen does not contain any neutron.

(b) No. It is neutral.

Question 11.

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

Answer:

Thomson’s Atomic Model:

According to Thomson’s atomic model, an atom is made of positively charged substances in the form of a sphere. Electrons are embedded into this sphere, and the total positive charge of the sphere is equal to the total negative charge of electrons, and hence, the atom remained electrically neutral. This model was not accepted because it was unable to explain how positively charged particles were shielded from negatively charged particles without getting neutralised.

 

Thomson's Atomic Model with example Thomson's Atomic Model:
Thomson’s atomic model Plum pudding

 

Question 12.

Which sub-atomic particle was discovered by

(a) Thomson

(b) Goldstein

(c) Chadwick

Answer:

(a) Thomson discovered particles.

(b) Goldstein discovered protons.

(c) Chadwick discovered neutrons.

Question 13.

Name the sub-atomic particle whose charge is:

(a) +1

(b) -1

(c) 0

Answer:

(a) Proton

(b) Electron

(c) Neutron

Question 14.

(a) Which metal did Rutherford select for his α particle scattering experiment and why?

(b) What do you think would be the observation of α particle scattering experiment if carried out on

(i) heavy nucleus like platinum

(ii) light nuclei like lithium.

Answer:

(a) He selected a gold foil because he wanted as thin a layer as possible and gold is the most malleable metal.

(b) (i) Heavy metals such as platinum will show the same observation with alpha particle as shown by gold foil

(ii) Light nuclei like may even push the light nucleus aside and may not deflected back.

Question 15.

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

Answer:

According to Rutherford’s model of an atom, the subatomic particle in a nucleus is a proton.

Question 16.

Which part of atom was discovered by Rutherford?

Answer:

The nucleus was discovered by Rutherford.

Question 17.

How was it shown that atom has empty space?

Answer:

Rutherford performed an experiment by allowing a stream of alpha particles to pass through a very thin gold foil. He observed that alpha particles pass through the metal foil without deviating from their path. This shows that an atom contains a large empty space called nuclear space.

Question 18.

State one major drawback of Rutherford’s model

Answer:

One major drawback of Rutherford’s model was the comparison of electrons with the planets in the solar system.

Thus, when an electron moved around the nucleus continually, it should radiate energy, i.e. lose energy. As a result it should be gradually pulled towards the nucleus and end up colliding with it. This should result in the total collapse of the atom.

However, we know that the atom is structurally stable. Thus, Rutherford’s model could not explain this stability.

Question 19.

In the figure given alongside

In the figure given alongside

(a) Name the shells denoted by A,B, and C. Which shell has least energy

(b) Name X and state the charge on it

(c) The above sketch is of …………. Model of an atom

Answer:

(a)

(i)  A is for K shell or I shell.

(ii)  is for L shell or II shell.

(iii)  is for M shell or III shell.

Shell K has the minimum amount of energy.

(b)  X is a nucleus; it is positively charged.

(c)  The above sketch is of Bohr model of an atom.

Question 20.

Give the postulates of Bohr’s atomic model

Answer:

(i) Atom has a central nucleus surrounded by electrons.

(ii) The electrons revolve around the nucleus in definite circular paths called orbits.

(iii) Each orbit has fixed energy. Therefore, these orbits are also known as energy levels or energy shells.

(iv) These orbits or energy levels are represented either by a number 1, 2, 3,… known as the principal quantum number (n) of the orbit or by K, L, M,….

(v) There is no change of energy of electrons as long as they keep revolving in the same energy level and the atom remains stable. Electrons can jump from the higher orbit to the lower orbit when they lose energy and jump to the next when they gain energy.

—  : End of Atomic Structure and Chemical Bonding Exe-4A Answer Class-9 ICSE Chemistry Solutions :–

Return to  Return to Concise Selina ICSE Chemistry Class-9 

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