Worksheet: Atoms and Molecules

# Worksheet: Atoms and Molecules - Science Class 9

Q.1. The maximum number of electrons in L shell is
(a)
8
(b)
18
(c)
28
(d)
38

Q.2. Which of the following statements is correct?
(a) Cathode rays travel in straight line and have momentum.
(b) Cathode rays travel in straight line and have no momentum
(c) Cathode rays do not travel in straight line but have Momentum.
(d) Cathode rays do not travel in straight line and have no momentum.

Q.3. Oxygen is –
(a) Monovalent
(b) Bivalent
(c) Trivalent
(d) Tetravalent

Q.4. Molecular mass of water (H2O) is
(a) 18g
(b) 8g
(c) 33g
(d) 34g

Q.5. Atomicity of chlorine and Argon is
(a) Diatomic and Monoatomic
(b) Monoatomic and Diatomic
(c) Monoatomic and Monoatomic
(d) Diatomic and Diatomic

Q.6. Stat the properties of cathode rays?

Q.7. Define the terms:
(a) Atomic number
(b) Mass number

Q.8. State the law of constant Proportion?

Q.9. Which postulate of Dalton’s atomic theory can explain the law of definite proportions?

Q.10. Which element will be more reactive and why → the element whose atomic number is 10 or the one whose atomic number is 11?

Q.11. What is the mass of 0.2 mole of oxygen atoms?

Q.12. The mass of an atom of element (X) is 2.0 × 10–23 g. Calculate its atomic mass.

Q.13. Calculate the molar mass of Nitric acid.

Q.14. Explain why the number of atoms in one mole of hydrogen gas is double the number of atoms in one mole of helium gas.

Q.15. If the valency of carbon is 4 and that of sulphur is 2, what is the chemical formula and name of the compound formed between carbon and sulphur atoms?

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## Science Class 9

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## FAQs on Worksheet: Atoms and Molecules - Science Class 9

 1. What is an atom?
Ans. An atom is the smallest unit of matter that retains the chemical properties of an element. It consists of a nucleus, which contains positively charged protons and uncharged neutrons, surrounded by negatively charged electrons.
 2. How are atoms and molecules related?
Ans. Atoms are the building blocks of molecules. Molecules are formed when two or more atoms chemically combine together through chemical bonds. These atoms can be of the same element or different elements.
 3. What is the difference between an atom and a molecule?
Ans. An atom is a single particle that cannot be divided into smaller units without losing its chemical properties. On the other hand, a molecule is a group of atoms held together by chemical bonds. A molecule can consist of two or more atoms.
 4. How do atoms and molecules behave in chemical reactions?
Ans. In a chemical reaction, atoms and molecules rearrange to form new substances. The bonds between atoms in the reactant molecules break, and new bonds form between the atoms to create the products. The total number of atoms remains the same, but their arrangement changes.
 5. Can atoms and molecules be seen with a microscope?
Ans. Atoms and molecules are too small to be seen with a traditional light microscope. However, they can be visualized using advanced techniques such as scanning tunneling microscopy or atomic force microscopy. These techniques allow scientists to observe individual atoms and molecules on a surface.

## Science Class 9

66 videos|355 docs|97 tests

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