Chemistry Worksheets Class 9 on Chapter 3 Atoms and Molecules with Answers - Set 1

Atoms and molecules play an important role in chemical reactions. An atom is a small piece of matter that possesses the properties of the element. Some atoms exist independently of one another by forming ions and molecules. Molecules are formed when one or more atoms form chemical bonds. It is the element’s smallest constituent that exhibits its properties. Molecules can be formed by chemical bonding between two or more atoms.

Download PDF of Class 9 Chemistry Worksheet Chapter 3 Atoms and Molecules – Set 1

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CBSE Class 9 Chemistry Worksheet Chapter 3 Atoms and Molecules – Set 1

Q1. The atomic number of an element is 13. What will be the number of electrons in its ion?

a.) 13

b.) 12

c.) 11

d.) 10

Q2. The formula of a compound is A₃B₂. The valency of element B will be:

a.) 2

b.) 3

c.) 1

d.) Cannot be determined

Q3. Atoms of the same element combine to form:

a.) molecules

b.) ions

c.) atoms

d.) compounds

Q4. The correct symbol of lead is-

a.) L

b.) Le

c.) Pb

d.) Pu

Q5. The discovery of ___ proved that the atom is divisible.

a.) protons

b.) electrons

c.) neutrons

d.) All of the above

Q6. What is the Avogadro constant?

Q7. The relative atomic mass of the oxygen atom is 16. Explain its meaning.

Q8. What is the difference between 2N and N₂?

Q9. What were the drawbacks of Dalton’s atomic theory?

Q10. Define the Law of conservation of mass.

Q11. What is meant by a molecule? Give examples.

Q12. Define atomic mass.

Q13. Calculate the molecular mass of the following compounds:

(Atomic masses: C = 12 𝛍, H = 1 𝛍, Cl = 35.5 𝛍, S = 32 𝛍, O = 16 𝛍, Na = 23 𝛍)

a.) Chloroform

b.) Sulphuric acid

c.) Sodium hydroxide

Q14. What are ions?

Q15. Fill in the blanks.

a.) Clusters of atoms that act as an ion are called ___ ions

b.) A chemical formula is also known as a ___.

c.) The valency of an ion is ___ to the charge on the ion.

d.) The mass of 1 mole of a substance is called its ____.

e.) The formula mass of Na₂O is ___.

Q16. How many grams of oxygen gas contain the same number of molecules as 16 grams of sulphur dioxide gas? (O = 16 𝛍, S = 32 𝛍)

Q17. Write the symbols of the following:

a.) Copper

b.) mercury

c.) iron

d.) silver

e.) gold

f.) argon

h.) zinc

Q18. Write the chemical formula of the following compound:

a.) Magnesium chloride

b.) Calcium oxide

c.) Copper nitrate

d.) Aluminium chloride

Q19. a.)The atomic number of three elements A, B and C are 9, 10 and 13 respectively. Which of them will form a cation?

b.) Give an example to show the law of conservation of mass applies to physical changes also.

Q20. a.) What is meant by the molar mass of a substance? State the unit in which molar mass is usually expressed.

b.) Calculate the molar masses of the following substances-

i.) Ozone molecule O₃

ii.) Ethanoic acid CH₃COOH

c.) Calculate the number of molecules in 4g of oxygen.

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Read Also:

• Difference Between An Atom And A Molecule
• Atoms and Molecules Questions
• Class 9 Chemistry Chapter 3 Atoms and Molecules MCQs
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