Molecules

Introduction

A molecule is the smallest unit of a compound or element that retains its chemical properties.
It is formed when two or more atoms combine chemically through chemical bonds.
Molecules are the basic building blocks of compounds, gases, living cells, and industrial chemicals.

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Key Characteristics of Molecules

• Made of two or more atoms (same or different)
• Held together by chemical bonds (usually covalent)
• Can exist in solid, liquid, or gaseous state
• Represented by chemical formulas (e.g., H₂O, O₂, CO₂)
• Can be diatomic, triatomic, or polyatomic

📝 PYQ (BPSC): What is H₂O an example of? → Molecule
📝 Expected MCQ: The smallest unit of a compound is? → Molecule

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Types of Molecules

1. Elemental Molecules

• Made of same type of atoms
• Examples:
  • O₂ (oxygen gas)
  • N₂ (nitrogen gas)
  • Cl₂ (chlorine)

2. Compound Molecules

• Made of different types of atoms
• Examples:
  • H₂O (water)
  • CO₂ (carbon dioxide)
  • CH₄ (methane)
  • NaCl (salt)

📝 Expected MCQ: Which is a compound molecule? → CO₂
📝 Expected MCQ: Oxygen molecule contains how many atoms? → 2

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Chemical Bonds in Molecules

• Covalent Bond: Atoms share electrons (e.g., H₂, O₂, CH₄)
• Ionic Bond: One atom donates electrons to another (e.g., NaCl)
• Polar Covalent Bond: Unequal sharing (e.g., H₂O)

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Molecular Formulas vs. Atomic Formulas

📝 Expected MCQ: What is the molecular formula of water? → H₂O
📝 Expected MCQ: NH₃ is the formula of? → Ammonia

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Importance in Daily Life

• Water (H₂O): Universal solvent, agriculture, life processes
• Carbon Dioxide (CO₂): Photosynthesis, climate
• Methane (CH₄): Biogas fuel
• Oxygen (O₂): Essential for respiration
• Glucose (C₆H₁₂O₆): Energy source in cells
• Urea (NH₂CONH₂): Common nitrogen fertilizer

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Bihar-Specific Relevance

🌾 Agriculture

• Urea, ammonia, and pesticide molecules critical for farming
• Soil testing kits use molecule-based chemical indicators
• Fertilizer plants in Barauni and associated schemes (PM Urea Subsidy)

🧪 Health & Education

• Molecules in medicines (e.g., paracetamol) taught in Bihar's intermediate science syllabus
• Public health schemes promote use of ORAL REHYDRATION SALTS (ORS) — NaCl, KCl, Glucose molecules

🌱 Renewable Energy

• CH₄ (methane) from rural biogas plants fuels cooking and electricity in Bihar villages

📝 Expected MCQ: Molecule used as nitrogen fertilizer? → Urea

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PYQs + Expected MCQs

📝 PYQ (BPSC): What is formed by chemical bonding of two atoms? → Molecule
📝 PYQ: What is the smallest unit of a compound? → Molecule
📝 Expected MCQ: Which molecule provides energy to human body? → Glucose
📝 Expected MCQ: Which molecule is abundant in biogas? → Methane (CH₄)
📝 Expected MCQ: Molecule of oxygen has how many atoms? → 2
📝 Expected MCQ: Formula of ammonia? → NH₃

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Quick Revision Points

• Molecule = Two or more atoms bonded
• Types: Elemental (O₂), Compound (CO₂)
• Bonds: Covalent, Ionic
• Water = H₂O, Oxygen = O₂, Methane = CH₄
• Bihar: Molecules in urea, methane, pesticides, ORS
• Taught in school syllabus and used in state’s agriculture & energy sectors

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Sources Used

• NCERT Science Class 9 – Atoms and Molecules
• Lucent GK – Chemistry Section
• Drishti Science Quick Book
• Ghatna Chakra + EduTeria BPSC PYQs
• Bihar School Education Board Syllabus – Class 10 & 12
• Bihar Agriculture Department – Urea & Fertilizer Use
• Ministry of Renewable Energy – Biogas Bihar Reports