Understanding atoms and molecules becomes easier when students practice questions regularly. This Chapter 9 Atomic Foundations of Matter Class 9 Worksheet PDF is designed to help students improve their concepts through written practice. It includes different types of questions based on atoms, molecules, chemical symbols, valency, chemical formulas, and molecular mass calculations.
These Worksheets are prepared according to the latest CBSE Board Class 9 Science syllabus to support students during revision and exam preparation. Students can use this practice sheet to check how well they understand important concepts from the chapter.
Our Class 9 Worksheets help learners develop problem-solving skills by providing concept-based exercises. This Class 9 Science Worksheet focuses only on written questions, including short answers, numerical problems, formula writing practice, and competency-based questions.
Download the worksheet, solve the questions, and use the answer key to evaluate your preparation.
Download Class 9 Atomic Foundations of Matter Worksheet PDF
Students can download the Class 9 Science Chapter 9 Atomic Foundations of Matter Worksheet PDF with Answers for extra practice. The worksheet is useful for revision before tests and school examinations.
This printable worksheet includes:
- Concept-based Science questions
- Chemical formula writing practice
- Molecular mass calculation questions
- Application-based exercises
- Complete answer key for self-checking
Practicing this worksheet helps students understand how atoms combine, how chemical formulas are written, and how different laws explain the nature of matter.
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Class 9 Atomic Foundations of Matter Worksheet Questions
Section A: Very Short Answer Questions
1. What is an atom?
2. Define a molecule.
3. Who proposed the atomic theory of matter?
4. State the law of conservation of mass.
5. What is meant by atomic mass?
6. Define valency of an element.
7. What are chemical symbols?
8. Write the symbol of the following elements:
(a) Sodium
(b) Potassium
(c) Calcium
9. What is an ion?
10. Name the positively and negatively charged ions.
Section B: Short Answer Questions
11. Explain any three postulates of Dalton’s atomic theory.
12. Differentiate between atoms and molecules.
13. Why are chemical symbols useful in Science?
14. Explain the law of constant proportions with an example.
15. What is the difference between an element and a compound?
16. Why do atoms combine to form molecules?
17. Explain the formation of ions with examples.
18. Write two differences between cations and anions.
19. How does valency help in writing chemical formulas?
20. Why is atomic mass important in chemistry calculations?
Section C: Numerical Practice Questions
21. Calculate the molecular mass of water (H₂O).
(Atomic mass: H = 1 u, O = 16 u)
22. Find the molecular mass of carbon dioxide (CO₂).
(Atomic mass: C = 12 u, O = 16 u)
23. Calculate the molecular mass of calcium carbonate (CaCO₃).
(Ca = 40 u, C = 12 u, O = 16 u)
24. Find the molecular mass of sulphuric acid (H₂SO₄).
(H = 1 u, S = 32 u, O = 16 u)
25. Calculate the formula unit mass of sodium chloride (NaCl).
(Na = 23 u, Cl = 35.5 u)
26. Find the molecular mass of ammonia (NH₃).
27. Calculate the molecular mass of methane (CH₄).
28. A compound contains hydrogen and oxygen in the ratio 1:8 by mass. Which law of chemical combination does this represent? Explain.
Section D: Chemical Formula Practice Questions
29. Write the chemical formula of magnesium chloride using valency.
30. Write the formula of aluminium oxide.
31. Find the chemical formula of calcium chloride.
32. Write the formula of sodium carbonate.
33. Write the chemical formula of potassium nitrate.
34. Write the formula of calcium hydroxide.
35. Write the formula of ammonium sulphate.
Section E: Competency-Based Questions
36. A student mixed two substances during an experiment. The total mass before and after the reaction remained the same. Which law does this prove? Explain.
37. A compound always contains the same elements combined in the same proportion by mass. Identify the law and explain its importance.
38. A student wrote the formula of magnesium oxide as Mg₂O₂. Is it correct? Give reason.
39. Why is it important to understand valency before writing chemical formulas?
40. How did Dalton’s atomic theory help scientists understand the structure of matter?
Class 9 Atomic Foundations of Matter Worksheet Answer Key
1. An atom is the smallest particle of an element that retains the chemical properties of that element. Atoms combine together to form molecules and compounds.
2. A molecule is a group of two or more atoms chemically bonded together. It can be made of atoms of the same element or different elements.
3. John Dalton proposed the atomic theory of matter in 1808.
4. The law of conservation of mass states that mass can neither be created nor destroyed during a chemical reaction. The total mass of reactants is always equal to the total mass of products.
5. Atomic mass is the mass of an atom expressed in atomic mass units (u). It shows how heavy an atom of an element is compared to other atoms.
6. Valency is the combining capacity of an atom. It represents the number of electrons an atom can lose, gain, or share to form chemical bonds.
7. Chemical symbols are short representations of the names of elements. They are usually written using one or two letters from the element name.
8. (a) Sodium – Na
(b) Potassium – K
(c) Calcium – Ca
9. An ion is an atom or group of atoms that carries an electric charge due to the loss or gain of electrons.
10. Positively charged ions are called cations, and negatively charged ions are called anions.
11. Three postulates of Dalton’s atomic theory are:
All matter is made up of very small particles called atoms.
Atoms of the same element have the same properties and mass.
Atoms combine in simple whole-number ratios to form compounds.
12. An atom is the smallest particle of an element that can take part in a chemical reaction, while a molecule is formed when two or more atoms combine chemically. Atoms may or may not exist independently, but molecules can exist independently.
13. Chemical symbols are useful because they provide a simple and universal way to represent elements. They make writing chemical reactions and formulas easier.
14. The law of constant proportions states that a chemical compound always contains the same elements combined together in a fixed proportion by mass. For example, water always contains hydrogen and oxygen in the mass ratio of 1:8.
15. An element is a pure substance made up of only one type of atom, while a compound is a substance formed when two or more different elements chemically combine in a fixed ratio.
16. Atoms combine to form molecules because they become more stable by completing their outermost electron shells through chemical bonding.
17. Ions are formed when atoms lose or gain electrons. Atoms losing electrons become positively charged cations, while atoms gaining electrons become negatively charged anions. For example, Na⁺ is a cation and Cl⁻ is an anion.
18. Cations are positively charged ions formed by the loss of electrons, whereas anions are negatively charged ions formed by the gain of electrons. Example: Sodium ion (Na⁺) is a cation, and chloride ion (Cl⁻) is an anion.
19. Valency helps in writing chemical formulas because it shows how many atoms of one element can combine with atoms of another element to form a stable compound.
20. Atomic mass is important in chemistry calculations because it helps determine molecular mass, formula unit mass, and the quantities of substances involved in chemical reactions.
21. Molecular mass of H₂O:
= (2 × Atomic mass of H) + (1 × Atomic mass of O)
= (2 × 1) + 16
= 2 + 16
= 18 u
22. Molecular mass of CO₂:
= Atomic mass of C + (2 × Atomic mass of O)
= 12 + (2 × 16)
= 12 + 32
= 44 u
23. Molecular mass of CaCO₃:
= Atomic mass of Ca + Atomic mass of C + (3 × Atomic mass of O)
= 40 + 12 + (3 × 16)
= 40 + 12 + 48
= 100 u
24. Molecular mass of H₂SO₄:
= (2 × H) + S + (4 × O)
= (2 × 1) + 32 + (4 × 16)
= 2 + 32 + 64
= 98 u
25. Formula unit mass of NaCl:
= Atomic mass of Na + Atomic mass of Cl
= 23 + 35.5
= 58.5 u
26. Molecular mass of NH₃:
= Atomic mass of N + (3 × Atomic mass of H)
= 14 + (3 × 1)
= 14 + 3
= 17 u
27. Molecular mass of CH₄:
= Atomic mass of C + (4 × Atomic mass of H)
= 12 + (4 × 1)
= 12 + 4
= 16 u
28. The given situation represents the law of constant proportions. This law states that a chemical compound always contains the same elements combined in the same fixed ratio by mass.
29. The chemical formula of magnesium chloride is MgCl₂. Magnesium has valency 2 and chlorine has valency 1, so one magnesium atom combines with two chlorine atoms.
30. The chemical formula of aluminium oxide is Al₂O₃. Aluminium has valency 3 and oxygen has valency 2.
31. The chemical formula of calcium chloride is CaCl₂. Calcium has valency 2 and chlorine has valency 1.
32. The chemical formula of sodium carbonate is Na₂CO₃.
33. The chemical formula of potassium nitrate is KNO₃.
34. The chemical formula of calcium hydroxide is Ca(OH)₂.
35. The chemical formula of ammonium sulphate is (NH₄)₂SO₄.
36. The experiment proves the law of conservation of mass. According to this law, the total mass of substances before a chemical reaction is equal to the total mass after the reaction because matter is neither created nor destroyed.
37. The law described is the law of constant proportions. It explains that every pure chemical compound contains the same elements in a fixed proportion by mass, regardless of its source.
38. The formula Mg₂O₂ is incorrect because chemical formulas are written in the simplest whole-number ratio. Magnesium has valency 2 and oxygen has valency 2, so the correct formula is MgO.
39. Understanding valency is important because it helps determine how atoms combine with each other and allows us to write correct chemical formulas of compounds.
40. Dalton’s atomic theory helped scientists understand that matter is made up of tiny particles called atoms. It explained chemical reactions, formation of compounds, and the basic principles of chemical combination.
Topics Covered in Atomic Foundations of Matter Worksheet
This Atomic Foundations of Matter Class 9 Worksheet with Answers covers all important practice topics from the chapter.
Students will practice:
- Atoms and molecules
- Dalton’s atomic theory
- Laws of chemical combination
- Law of conservation of mass
- Law of constant proportions
- Chemical symbols
- Elements and compounds
- Ions, cations, and anions
- Valency of elements
- Chemical formula writing
- Molecular mass calculations
Learning Outcomes from this Worksheet
After completing this worksheet, students will be able to:
- Understand the basic structure of matter
- Explain atoms and molecules clearly
- Apply Dalton’s atomic theory concepts
- Write chemical formulas using valency
- Calculate molecular and formula unit mass
- Solve CBSE-style written Science questions
- Improve accuracy in chemistry-based problems
Benefits of Solving Atomic Foundations of Matter Worksheet
Regular practice of the Class 9 Science Chapter 9 Atomic Foundations of Matter Worksheet helps students build a strong chemistry foundation.
Key benefits include:
- Improves written answer practice
- Strengthens understanding of atoms and molecules
- Helps remember chemical symbols and formulas
- Builds confidence in numerical questions
- Supports preparation for CBSE exams
- Helps students identify weak topics before tests
This worksheet is a useful practice resource for students who want to revise concepts and improve their Science performance.
