Journey Inside the Atom Class 9 Worksheet with Answers Science Chapter 8

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Class 9 Journey Inside the Atom Worksheet

Worksheet On Journey Inside the Atom Class 9

Journey Inside the Atom Worksheet Class 9

→ Matter: Anything that has mass and occupies space.

→ Atom: The smallest unit of an element that retains its chemical properties.

→ Atomic Theory: A scientific theory stating that matter is composed of atoms.

→ Parmanu: The smallest indivisible particle of matter as proposed by Acharya Kanada.

→ Atomos: Greek term meaning indivisible particles of matter.

→ Atomic Model: A representation used to describe the structure of an atom.

→ Radiation: Energy emitted in the form of particles or waves.

→ Radioactivity: The emission of radiation from certain atoms.

→ Cathode Rays: Streams of negatively charged particles (electrons) observed in a discharge tube.

→ Electron (e^–): A negatively charged subatomic particle present outside the nucleus.

→ Cathode Ray Tube: A vacuum-sealed glass tube used to study cathode rays and discover electrons.

→ Thomson’s Model: A model in which electrons are embedded in a positively charged sphere.

→ Alpha Particles (a-particles): Positively charged particles used in scattering experiments.

→ Nucleus: The small, dense, positively charged central part of an atom.

→ Proton (p⁺): A positively charged subatomic particle present in the nucleus.

→ Neutron (n⁰): A neutral subatomic particle present in the nucleus.

→ Scattering: The deflection of particles from their straight path.

→ Rutherford’s Model: A model in which the atom has a central nucleus and electrons revolve around it.

→ Bohr’s Model: A model in which electrons move in fixed energy levels or shells around the nucleus.

→ Energy Levels (Shells): Fixed regions around the nucleus where electrons are present.

→ Subatomic Particles: Particles smaller than atoms electrons, protons, and neutrons.

→ Nuclear Force: The force that holds protons and neutrons together in the nucleus.

→ Chemical Symbols: The standard short representation of an element using letters.

→ IUPAC: International body that standardises names and symbols of elements.

→ Atomic Number (Z): The number of protons present in the nucleus of an atom.

→ Mass Number (A): The total number of protons and neutrons in the nucleus.

→ Nucleons: The particles present in the nucleus (protons and neutrons).

→ Electronic Configuration: The distribution of electrons in different shells of an atom.

→ Valency: The combining capacity of an atom.

→ Valence Shell: The outermost shell of an atom.

→ Valence Electrons: Electrons present in the outermost shell of an atom.

→ Octet: A stable arrangement of eight electrons in the outermost shell.

→ Isotopes: Atoms of the same element having the same atomic number but different mass numbers.

→ Unified Atomic Mass Unit (u): The unit used to express atomic masses.

→ Average Atomic Mass: The weighted average of the masses of isotopes of an element based on their abundance.

→ Isobars: Atoms of different elements having the same mass number but different atomic numbers.

→ Electron Cloud: The region around the nucleus where electrons are most likely to be found.

Class 9 Science Exploration Chapter 8 Worksheet

Class 9 Science Journey Inside the Atom Worksheet

A. Multiple-Choice Questions

Question 1.
The first model of an atom was given by
(a) N. Bohr
(b) E. Goldstein
(c) Rutherford
(d) J.J. Thomson.

Question 2.
An atom with 3 protons and 4 neutrons will have a valency of
(a) 3
(b) 7
(c) 1
(d) 4

Question 3.
Which statement is correct about atoms?
(a) Atoms are always visible.
(b) Atoms are indivisible according to modern theory.
(c) Atoms have no empty space.
(d) Atoms contain subatomic particles.

Question 4.
What is the charge on an electron?
(a) +1
(b) 0
(c) -1
(d) +2

Question 5.
A brief information about two atoms X and Y is given:
X: Atomic number = 7, Mass number = 14
Y: Atomic number = 7, Mass number = 15

Which of the following is correct about these two atoms?
(a) Electronic configuration of X is 2, 8, 4 while that of Y is 2, 8, 5.
(b) Both X and Y contain 7 neutrons.
(c) X has 2 electron shells while Y has 3 electron shells.
(d) Both X and Y have 5 valence electrons.

Question 6.
Which of the following are isobars?

(a) I and II
(b) II and III
(c) I, II and IV
(d) II, III and Iv

Question 7.
Which of the following is not an isotope of the other three?

Question 8.
Hydrogen exists in three isotopic forms, H, H, H respectively known as protium, deuterium and tritium.
Why are all the isotopes neutral in nature?
(a) All the isotopes contain same number of neutrons hence, they are electrically neutral.
(b) All the isotopes have one electron and one proton, hence they are neutral.
(c) All the isotopes have one proton and one neutron, hence they are neutral.
(d) Equal number of protons and neutrons in the isotopes make them neutral.

Question 9.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose the appropriate answer.
Assertion (A): Atom is electrically neutral.
Reason (R): A neutral particle, neutrori, is present in the nucleus of atom.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A.
(c) A is true, but R is false.
(d) A is false, but R is true.

Question 10.
This question consists of an Assertion (A) and a Reason (R). Read the Assertion and Reason and choose the appropriate answer.
Assertion (A): Thomson’s model explained the presence of a nucleus.
Reason (R): Positive charge was uniformly distributed in the atom.
(a) Both A and R are true, and R is the correct explanation of A.
(b) Both A and R are true, but R is not the correct explanation of A. U
(c) A is true, but R is false.
(d) A is false, but R is true.

B. State True (T) or False (F).

Question 1.
All matter is made up of atoms.

Question 2.
Ancient ideas about atoms were based on experiments.

Question 3.
Dalton proposed that atoms are indivisible particles.

Question 4.
Isotopes differ in the number of electrons.

Question 5.
Electrons are located inside the nucleus.

Question 6.
Atomic number is equal to the number of protons.

Question 7.
Maximum number of electrons in a shell is given by 2n².

Question 8.
K-shell can hold a maximum of 8 electrons.

Question 9.
Electrons fill shells starting from the outermost shell.

Question 10.
Noble gases are highly reactive.

C. Fill in the blanks.

Question 1.
Matter is made up of tiny particles called _____ .

Question 2.
Most of the mass of an atom is concentrated in the ______.

Question 3.
Electrons can move to higher energy levels by _____ energy.

Question 4.
Protons and neutrons together are called _____ .

Question 5.
Chlorine occurs in nature in _______ isotopic forms.

Question 6.
An atom with valency zero is highly _____ .

Question 7.
The outermost shell is called the ______ shell.

D. Assign one word to the following.

Question 1.
Scientist who discovered neutron.

Question 2.
Combining capacity of an atom.

Question 3.
Neutral particle present in the nucleus.

Question 4.
Electrons present in the outermost shell.

Question 5.
Energy levels of electrons in an atom. _____

E. Match the Columns.

Question 1.
Match the symbols given in Column I with the names of the elements given in Column II.

Column I	Column
(i) W	(a) Copper
(ii) Au	(b) Iron
(iii) Cu	(c) Gold
(iv) Fe	(d) Silver
(v) Ag	(e) Tungsten

Question 2.
Match the elements given in Column I with their corresponding electronic configurations given in Column II.

Column I	Column II
(i) Chlorine	(a) 2,3
(ii) Lithium	(b) 2,7
(iii) Magnesium	(c) 2,1
(iv) Boron	(d) 2, 8,7
(v) Fluorine	(e) 2, 8,2

F. Differentiate between the following.

Question 1.
Atom and Molecule

Question 2.
Isotopes and Isobars

Question 3.
Atomic Number and Mass Number

G. Very Short Answer Type Questions

Question 1.
Name three fundamental particles of an atom.

Question 2.
Is it possible for the atom of an element to have one electron, one proton and no neutron? If so, name the element.

Question 3.
What do cathode rays consist of?

H. Short Answer Type Questions

Question 1.
How did the discovery of subatomic particles change Dalton’s atomic theory?

Question 2.
Why did Rutherford select a gold foil in his a-ray scattering experiment?

Question 3.
Explain why atoms are considered electrically neutral, even though they contain charged particles.

I. Long Answer Type Questions

Question 1.
Rutherford’s model explained the presence of a nucleus but failed to explain atomic stability. Explain why this limitation was important and how it led to further development of atomic models.

Question 2.
Explain isotopes with examples and mention their uses.

A. Give reasons for the following.

Question 1.
Atoms are electrically neutral.

Question 2.
The nucleus occupies a very small space inside the atom.

Question 3.
Isotopes have similar chemical properties.

Question 4.
Atomic number is considered the identity of an element.

Question 5.
Scientists concluded that atoms are divisible.

Question 6.
The outermost shell of an atom cannot have more than eight electrons.

Question 7.
Elements with more than four valence electrons tend to gain electrons.

B. Read the paragraph and answer the following questions.
Rutherford’s atomic model has certain limitations. To overcome these limitations, Bohr proposed a new atomic model in which electrons are assumed to move in specific permitted energy states or shells around the nucleus. Each state has a definite energy, and when an electron remains in one such state, its energy remains constant. However, electrons can jump from one shell to another by absorbing or releasing a fixed amount of energy. This model explained the limitations of the previous model and introduced the concept of fixed energy levels.

Question 1.
What limitation of Rutherford’s model did Bohr try to explain?

Question 2.
According to Bohr’s model, where do electrons move?

Question 3.
Do electrons lose energy while moving in a shell? Give reason.

Question 4.
What happens when an electron moves from one energy level to another?

Question 5.
Why is Bohr’s model considered important in atomic theory?

Question 6.
What is meant by a fixed energy level?

C. Identify the odd one out and give reason for your answer.

Question 1.
Protium, Lithium, Deuterium, Tritium
Reason:

Question 2.
Electron, Proton, Neutron, Alpha particle
Reason:

Question 3.
Thomson, Rutherford, Nucleus, Bohr
Reason:

Question 4.
Lithium, Helium, Nitrogen, Carbon
Reason:

D. Observe the given figure and answer the following questions.

Question 1.
In which direction do cathode rays travel in the tube?

Question 2.
What is the name of the negative electrode in a cathode ray tube?

Question 3.
What is the name of the positive electrode in a cathode ray tube?

Question 4.
What are the required conditions of voltage and pressure in a cathode ray tube experiment?

Question 5.
What conclusion can be drawn from experiments showing cathode rays produced from different gases and electrodes?

Learn By Doing

A. A group of students in a school laboratory is studying different atoms and their electronic configurations. During the activity, some entries in their observation table were accidentally erase(d) Using your knowledge of atomic number, protons, neutrons, electrons, and electronic configuration, help them complete the missing information correctly.

B. Complete the schematic atomic structures of the following elements by showing how electrons are distributed in the K, L, and M shells.

C. Identify the atomic model shown below. Name the scientist who proposed this model. Also, write the main features and limitations of the model.

Atomic Model: _______
Scientist: _______
Main Features: _______

Limitations: ____

Explore With Curiosity

A. During an experiment, a student replaced all electrons in an atom with hypothetical particles having the same charge but much greater mass. Which properties of the atom would remain unchanged, and which property would change significantly?

B. A student compared neon and sodium atoms. Neon has the electronic configuration 2, 8, while sodium has 2, 8,1. Why is neon chemically stable while sodium is highly reactive?

C. During a classroom activity on atomic structure, the teacher gave students information about an atom that contains 31 protons and has a mass number of 70. The students were asked to find the number of neutrons and electrons present in the atom.

D. During a laboratory activity, Riya learns that bromine exists naturally as two isotopes: ⁷⁹Br and ⁸¹Br. Her teacher explains that 49.7% of bromine atoms are ⁷⁹, while 50.3% are ⁸¹Br. Riya wonders why the atomic mass of bromine in the periodic table is not exactly 79 u or 81 u. Help her calculate the average atomic
mass of bromine.

E. During a science exhibition, students prepared a chart showing the journey of the development of atomic models proposed by different scientists over time. Observe the following figures carefully. Identify and write the names of the atomic models in the spaces provided below.

Suggested Activities

A. Create an “Atomic Family Tree” chart showing the development of atomic models from Dalton to the modern atomic model. Include the scientist’s name, year, discovery, and limitation of each model.

B. Organise a role-play activity in which students act as scientists like Dalton, Thomson, Rutherford, and Bohr. Conduct a discussion or debate explaining how each atomic model improved the understanding of atomic structure.

C. Collect information about isotopes used in everyday life and prepare a short presentation on their applications in medicine, electricity generation, archaeology, and agriculture.

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