Understanding atoms and their structure is an important part of learning Chemistry. This Class 9 Science Chapter 8 Journey Inside the Atom Worksheet PDF is created to help students practice important concepts and improve their understanding of the chapter through written questions.
This worksheet includes practice questions based on atomic structure, subatomic particles, atomic models, electronic configuration, valency, isotopes, isobars, and atomic calculations. Students will get different types of questions that encourage them to think, solve, and apply concepts instead of only memorizing definitions.
Practicing Worksheets regularly helps students check their preparation level and understand where they need improvement. These chapter-wise Class 9 Worksheets are useful for homework practice, revision, and strengthening subject knowledge. Students can also explore more Class 9 Science Worksheets to practice other chapters and improve their Science preparation.
This worksheet is designed for CBSE Board Class 9 students who want extra practice after completing the chapter. Solve all questions carefully and check your answers to build confidence before exams.
Class 9 Journey Inside the Atom Worksheet with Answers PDF
The Class 9 Journey Inside the Atom Worksheet with Answers PDF provides students with structured practice questions to revise all major concepts from the chapter. It helps students understand how atoms are formed, how particles are arranged inside an atom, and how atomic properties are calculated.
This worksheet helps students practice:
- Structure of an atom
- Properties of electrons, protons, and neutrons
- Different atomic models
- Distribution of electrons in shells
- Atomic number and mass number calculations
- Valency of elements
- Isotopes and isobars
Students can use this worksheet for regular revision, classroom assignments, and self-practice to improve their understanding of Chemistry concepts.
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Journey Inside the Atom Practice Questions
Practice the following Class 9 Science Chapter 8 Journey Inside the Atom Worksheet questions to strengthen your understanding of atoms and their structure. Try solving each question before checking the answers.
Level 1: Concept Check
1. What is an atom?
2. Name the three main subatomic particles present inside an atom.
3. Write the electrical charge present on:
Proton
Electron
Neutron
4. Define atomic number.
5. What is mass number?
6. Where are protons and neutrons located inside an atom?
7. What is the nucleus of an atom?
8. Write two important features of Thomson’s atomic model.
9. Why was Thomson’s atomic model also called the plum pudding model?
10. Write two observations from Rutherford’s alpha particle scattering experiment.
11. What are energy shells in an atom?
12. Define valency.
Level 2: Application Practice
13. Explain why atoms are electrically neutral.
14. Write the difference between electrons and protons.
15. How was Rutherford’s model different from Thomson’s atomic model?
16. Explain Bohr’s model of an atom.
17. Write the electronic configuration of the following elements:
a. Oxygen (Atomic number 8)
b. Magnesium (Atomic number 12)
c. Chlorine (Atomic number 17)
18. An atom has atomic number 15 and mass number 31. Find:
a. Number of protons
b. Number of electrons
c. Number of neutrons
19. Find the valency of elements having the following electronic configurations:
a. 2,8,1
b. 2,8,7
20. Differentiate between isotopes and isobars.
21. Why is the mass of an atom mainly concentrated in the nucleus?
22. Write the maximum number of electrons that can be present in:
K shell
L shell
M shell
Level 3: Exam Practice
23. Explain Rutherford’s alpha particle scattering experiment and write its major conclusions.
24. Describe Bohr-Bury rules for the arrangement of electrons in different shells.
25. Draw the atomic structure of sodium with atomic number 11.
26. An element has 13 protons and 14 neutrons. Find its atomic number and mass number.
27. Explain why Rutherford’s atomic model could not explain the stability of atoms.
28. Write three differences between isotopes and isobars with examples.
Case-Based Questions
Read the passage and answer the questions.
A scientist performed an experiment by passing alpha particles through a thin gold foil. Most particles passed straight through, some were slightly deflected, and very few bounced back.
29. Identify the experiment mentioned above.
30. Name the scientist who performed this experiment.
31. What did this experiment prove about the structure of an atom?
Atoms of the same element can sometimes have different numbers of neutrons while keeping the same number of protons.
32. What are such atoms called?
33. Do these atoms have the same atomic number?
34. Give one example of these atoms.
Answers and Explanations
1. An atom is the smallest unit of matter that shows the properties of an element.
2. The three main subatomic particles are:
Electron
Proton
Neutron
3. Charges on particles:
Proton: Positive charge
Electron: Negative charge
Neutron: No charge
4. Atomic number is the total number of protons present inside the nucleus of an atom.
5. Mass number is the total number of protons and neutrons present in the nucleus.
Mass Number = Number of Protons + Number of Neutrons
6. Protons and neutrons are located inside the nucleus of an atom.
7. The nucleus is the small, dense central part of an atom that contains protons and neutrons.
8. Thomson’s atomic model suggested:
An atom is a positively charged sphere.
Electrons are embedded inside this positive sphere.
9. Thomson’s model was called the plum pudding model because electrons were arranged inside a positive sphere like dry fruits in a pudding.
10. Rutherford observed:
Most alpha particles passed straight through the foil.
Few particles were deflected from their path.
11. Energy shells are fixed paths around the nucleus where electrons revolve.
12. Valency is the combining capacity of an atom.
13. Atoms are neutral because they contain equal numbers of positively charged protons and negatively charged electrons.
14. Electrons are negatively charged particles found outside the nucleus, while protons are positively charged particles present inside the nucleus.
15. Rutherford suggested that atoms have a small positively charged nucleus, while Thomson suggested that positive charge was spread throughout the atom.
16. According to Bohr’s model:
Electrons move in fixed shells around the nucleus.
Each shell has a fixed energy level.
17. Electronic Configurations:
Oxygen (8): 2,6
Magnesium (12): 2,8,2
Chlorine (17): 2,8,7
18. Solution:
Atomic number = 15
Mass number = 31
Protons = 15
Electrons = 15
Neutrons = Mass number − Atomic number
= 31 − 15
Neutrons = 16
19. Valency:
a. 2,8,1 → Valency = 1
b. 2,8,7 → Valency = 1
20. Isotopes are atoms of the same element having different mass numbers. Isobars are atoms of different elements having the same mass number.
21. Most atomic mass is concentrated in the nucleus because protons and neutrons are present there.
22. Maximum electrons:
K shell = 2 electrons
L shell = 8 electrons
M shell = 18 electrons
23. Rutherford’s experiment showed that an atom contains a small, dense, positively charged nucleus and most of the atom is empty space.
24. Bohr-Bury rules explain the distribution of electrons in shells. The maximum number of electrons in a shell is calculated by the formula 2n².
25. Sodium atomic structure:
Electronic configuration of sodium (11):
2,8,1
It contains:
11 protons
11 electrons
26. Solution:
Protons = 13
Neutrons = 14
Atomic number = Number of protons
Atomic number = 13
Mass number = Protons + Neutrons
= 13 + 14
Mass number = 27
27. Rutherford’s model could not explain why moving electrons do not lose energy and fall into the nucleus.
28. Isotopes have the same atomic number but different mass numbers, while isobars have different atomic numbers but the same mass number.
29. Rutherford’s alpha particle scattering experiment.
30. Ernest Rutherford.
31. It proved that atoms have a small positively charged nucleus.
32. They are called isotopes.
33. Yes, isotopes have the same atomic number.
34. Example: Carbon-12 and Carbon-14.
Important Topics Covered in Journey Inside the Atom Worksheet
This worksheet covers important concepts from Class 9 Science Chapter 8:
- Structure of atom
- Subatomic particles
- Electron, proton, and neutron
- Discovery of atomic particles
- Thomson atomic model
- Rutherford atomic model
- Bohr atomic model
- Alpha particle scattering experiment
- Atomic number
- Mass number
- Electronic configuration
- Valency
- Isotopes
- Isobars
- Arrangement of electrons in shells
Common Mistakes Students Should Avoid
While solving the Journey Inside the Atom Worksheet, students should avoid these mistakes:
- Confusing atomic number and mass number
- Forgetting charges of subatomic particles
- Writing incorrect electronic configurations
- Mixing isotopes with isobars
- Not following shell filling rules
- Forgetting labels while drawing atomic structures
- Making calculation errors while finding neutrons
Regular practice can help students avoid these mistakes and improve their accuracy.
