3. Atoms and Molecules Class 9 Science [LATEST] Solutions Additional -Questions 3 in English - CBSE Study
NCERT Solutions for Class 9 Science are carefully prepared according to the latest CBSE syllabus and NCERT textbooks to help students understand every concept clearly. These solutions cover all important 3. Atoms and Molecules with detailed explanations and step-by-step answers for better exam preparation. Each Additional -Questions 3 is explained in simple language so that students can easily grasp the fundamentals and improve their academic performance. The study material is designed to support daily homework, revision practice, and final exam preparation for Class 9 students. With accurate answers, concept clarity, and structured content, these NCERT solutions help learners build confidence and score higher marks in their examinations. Whether you are revising a specific topic or preparing an entire chapter, this resource provides reliable and syllabus-based guidance for complete success in Science.
Class 9 English Medium Science All Chapters:
3. Atoms and Molecules
5. Additional -Questions 3
Additional -Questions:
Q1. What is atomicity?
Ans: The number of atoms contained in a molecule of a substance is called its atomicity.
Q2. How molecules are categrised on the base of atomicity?
Ans:
1. Monoatomic Molecules (Molecule having 1 atom)
2. Diatomic Molecules (molecule having 2 atoms)
3. Triatomic Molecules (molecules having 3 atoms)
4. Tetraatomic Molecules (molecules having 4 atoms)
5. Ployatomic Molecules (molecules having more than 4 molecules)
1. Atom
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The smallest particle of an element that cannot be divided further by chemical means.
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It retains all the properties of that element.
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Example: H (Hydrogen atom), O (Oxygen atom).
2. Molecule
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A group of two or more atoms (same or different) chemically bonded together.
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Example: H₂ (hydrogen molecule), H₂O (water molecule).
3. Ion
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A charged particle formed when an atom or molecule loses or gains electrons.
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Positive ions → Cations (formed by loss of electrons).
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Negative ions → Anions (formed by gain of electrons).
4. Atomicity
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The number of atoms present in one molecule of an element.
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Example:
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O₂ → Atomicity = 2
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P₄ → Atomicity = 4
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5. Anion
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A negatively charged ion.
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Formed by gain of electrons.
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Example: Cl⁻, O²⁻.
6. Cation
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A positively charged ion.
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Formed by loss of electrons.
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Example: Na⁺, Ca²⁺.
7. One mole atom
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The amount of a substance containing 6.022 × 10²³ atoms of that element.
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Example: 1 mole of carbon = 6.022 × 10²³ atoms of carbon.
8. One mole molecule
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The amount of a substance containing 6.022 × 10²³ molecules.
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Example: 1 mole of water (H₂O) = 6.022 × 10²³ molecules of H₂O.
9. Monoatomic
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A molecule that contains only one atom.
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Example: Noble gases (He, Ne, Ar).
10. Diatomic
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A molecule that contains two atoms.
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Example: H₂, O₂, Cl₂.
11. Triatomic
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A molecule that contains three atoms.
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Example: O₃ (ozone), H₂O (water).
12. Polyatomic
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A molecule that contains more than three atoms.
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Example: P₄ (phosphorus), CH₄ (methane), C₆H₁₂O₆ (glucose).
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