Science Exploration Notes Class 9 English Medium 2026-27

Science Exploration Chapter 9. Atomic Foundations of Matter

CBSE Notes New Syllabus: Class 9

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Chapter 9. Atomic Foundations of Matter

This assignment covers all the important concepts of the chapter, including the laws of chemical combination, Dalton's Atomic Theory, covalent bonding and ionic bonding. The questions follow the latest CBSE competency-based pattern and help strengthen conceptual understanding.

Chapter Assignment

1. One Word Answer

1. The scientist who proposed the Law of Conservation of Mass.
2. The scientist who proposed the Law of Constant Proportions.
3. The scientist who proposed the first Atomic Theory.
4. The smallest particle of an element.
5. A bond formed by sharing electrons.
6. A bond formed by transfer of electrons.
7. A positively charged ion.
8. A negatively charged ion.
9. The force that holds atoms together.
10. The common name of NaCl.

2. Fill in the Blanks

1. Mass is neither __________ nor __________ during a chemical reaction.
2. The Law of Constant Proportions was proposed by __________.
3. Atoms combine in simple __________ number ratios.
4. A covalent bond is formed by __________ of electrons.
5. An ionic bond is formed by __________ of electrons.
6. Sodium loses __________ electron to form Na⁺.
7. Chlorine gains __________ electron to form Cl⁻.
8. Water is a __________ compound.
9. NaCl is an __________ compound.
10. Chemical bonding helps atoms achieve __________ configuration.

3. True or False

1. Mass changes during a chemical reaction.
2. Every pure compound has a fixed composition.
3. Dalton proposed the first scientific Atomic Theory.
4. Covalent bonds are formed by electron transfer.
5. Ionic bonds are formed by electrostatic attraction.
6. Sodium gains an electron to form Na⁺.
7. Chlorine loses an electron to form Cl⁻.
8. Water is an ionic compound.
9. Atoms combine to become more stable.
10. NaCl is formed by ionic bonding.

4. Match the Following

5. Very Short Answer Questions

1. State the Law of Conservation of Mass.
2. Who proposed the Law of Constant Proportions?
3. Write one postulate of Dalton's Atomic Theory.
4. What is a covalent bond?
5. What is an ionic bond?
6. Define a cation.
7. Define an anion.
8. Why do atoms combine?
9. Write one example of a covalent compound.
10. Write one example of an ionic compound.

6. Short Answer Questions

1. Differentiate between physical and chemical changes.
2. Explain the Law of Conservation of Mass with an example.
3. State the Law of Constant Proportions and explain it with an example.
4. Describe the main postulates of Dalton's Atomic Theory.
5. Explain the formation of a hydrogen molecule (H₂).
6. Describe the formation of an oxygen molecule (O₂).
7. Explain the formation of hydrogen chloride (HCl).
8. Describe the formation of a water molecule (H₂O).
9. Explain the formation of sodium chloride (NaCl).
10. Differentiate between covalent and ionic bonds.

7. Long Answer Questions

1. Explain the two fundamental laws of chemical combination with suitable examples.
2. Describe Dalton's Atomic Theory along with its merits and limitations.
3. Explain how covalent bonds are formed with suitable examples.
4. Describe the formation of H₂, Cl₂ and O₂ using electron sharing.
5. Explain the formation of HCl and H₂O using electron-dot representation.
6. Describe the formation of NaCl through ionic bonding.
7. Differentiate between covalent compounds and ionic compounds.
8. Explain the importance of chemical bonding in the formation of compounds.

8. Case Study Questions

Case Study – 1

A student performs a chemical reaction in a sealed flask. The total mass of the flask and its contents remains the same before and after the reaction.

1. Which law is verified by this activity?
2. Who proposed this law?
3. Why should the reaction be carried out in a closed system?
4. State the law.

Case Study – 2

Water obtained from rain, rivers and laboratories always contains hydrogen and oxygen in the same fixed proportion by mass.

1. Which law explains this observation?
2. Who proposed this law?
3. Why is water called a pure compound?
4. Name another compound that follows this law.

Case Study – 3

A hydrogen atom shares one electron with another hydrogen atom to form H₂.

1. Which type of bond is formed?
2. How many electrons are shared?
3. Why do hydrogen atoms share electrons?
4. Name another molecule formed by covalent bonding.

Case Study – 4

Sodium transfers one electron to chlorine to form sodium chloride.

1. Which type of bond is formed?
2. Which ion is positively charged?
3. Which ion is negatively charged?
4. What force holds these ions together?

Case Study – 5

A student compares water and sodium chloride in the chemistry laboratory.

1. Which one is a covalent compound?
2. Which one is an ionic compound?
3. How are their bonds formed?
4. State one difference between them.

9. Competency-Based Questions

1. Why is the Law of Conservation of Mass valid only in a closed system?
2. How does the Law of Constant Proportions support Dalton's Atomic Theory?
3. Why do atoms combine to form compounds?
4. Why is electron sharing necessary in covalent bonding?
5. Explain why sodium loses an electron while chlorine gains one.
6. How do ionic compounds achieve stability?
7. Why are the properties of covalent and ionic compounds different?
8. Explain the importance of chemical bonding in everyday life.
9. How does electron transfer help in the formation of sodium chloride?
10. Differentiate between sharing and transfer of electrons with suitable examples.

10. HOTS Questions

1. How do the Laws of Chemical Combination support Dalton's Atomic Theory?
2. Why is the composition of a pure compound always fixed even when prepared by different methods?
3. Compare the formation of H₂O and NaCl based on electron behaviour.
4. Why are atoms more stable after chemical bonding than before bonding?
5. Explain why covalent compounds generally exist as molecules, whereas ionic compounds form crystal lattices.
6. How would chemistry be affected if atoms did not form chemical bonds?
7. Why is electron transfer not possible between two hydrogen atoms?
8. Explain how the type of bonding influences the properties of substances.
9. Compare covalent and ionic bonding using suitable examples from daily life.
10. Prepare a flow chart showing the sequence: Laws of Chemical Combination → Dalton's Atomic Theory → Chemical Bonding → Formation of Compounds.