Atoms

An atom is the smallest unit of matter that retains the properties of an element.
It consists of a central nucleus (containing protons and neutrons) and surrounding electrons.
All matter — gases, liquids, and solids — is made up of atoms.
Understanding atoms is fundamental to chemistry, physics, and even nuclear energy initiatives in India and Bihar.

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Basic Structure of an Atom

• Nucleus → Contains:
  • Protons (+ve charge)
  • Neutrons (no charge)
• Electron Shells → Electrons (-ve charge) revolve around nucleus in fixed orbits

📝 PYQ (BPSC): Which particle of atom has negative charge? → Electron

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Atomic Numbers and Mass

• Atomic Number (Z) = Number of protons = Number of electrons
• Mass Number (A) = Protons + Neutrons
• Isotopes = Same atomic number but different mass numbers

📝 Expected MCQ: Atom with same proton number but different neutron count is called? → Isotope

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Atomic Models

1. Dalton’s Atomic Theory (1808)

• Atoms are indivisible and indestructible
• All atoms of an element are identical
• Foundation of modern chemistry

2. Thomson Model (1897)

• Plum pudding model: Atom is a sphere of positive charge with electrons inside

3. Rutherford’s Model (1911)

• Discovered nucleus and proposed electrons revolve around it

4. Bohr’s Model (1913)

• Electrons revolve in fixed energy levels or orbits
• Energy is absorbed or emitted when electrons change orbits

📝 PYQ: Who discovered the nucleus? → Rutherford
📝 Expected MCQ: Which model introduced fixed electron orbits? → Bohr’s model

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Subatomic Particles

📝 Expected MCQ: Lightest subatomic particle? → Electron
📝 Expected MCQ: Which particle defines atomic number? → Proton

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Applications of Atomic Understanding

• Atomic Energy: Power plants like Kudankulam, research at BARC
• Carbon Dating: Used in archaeology (Isotopes like C-14)
• Medicine: Radiotherapy uses isotopes of atoms
• Nuclear bombs and reactors: Based on atomic fission (Uranium, Plutonium)

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Bihar-Specific Relevance

• Bihar schools and colleges use atomic concepts in basic science education
• In agriculture, understanding isotopes (e.g., P-32, N-15) helps in fertilizer research
• Awareness about radiation safety in medical diagnostics (X-ray, CT scan) is promoted
• Proposed inclusion of nuclear science modules in Bihar School Science Curriculum

📝 Expected MCQ: Isotopes used in fertilizer research? → N-15

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PYQs + Expected MCQs

📝 PYQ (BPSC): Who discovered the electron? → J.J. Thomson
📝 PYQ (BPSC): Atom’s nucleus was discovered by? → Rutherford
📝 Expected MCQ: Charge of neutron? → Zero
📝 Expected MCQ: What is the center of atom called? → Nucleus
📝 Expected MCQ: What are isotopes? → Same atomic number, different mass number

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Quick Revision Points

• Atom = Smallest unit of matter
• Made of Protons, Neutrons, Electrons
• Atomic number = Protons, Mass number = P + N
• Electron revolves in orbits (Bohr Model)
• Discoveries: Electron → Thomson, Nucleus → Rutherford
• Isotopes used in medicine, carbon dating, farming

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Sources Used

• NCERT Science Class 9–10 – Structure of the Atom
• Lucent GK – Chemistry Section
• Drishti Science Quick Book
• EduTeria + Ghatna Chakra PYQs (BPSC, CDPO)
• BARC India (Nuclear Science Use)
• Bihar State Science Education Portal
• Indian Nuclear Society Reports