🔬 STRUCTURE OF THE ATOM (MCQs Notes)
🔹 1. Basic Definition
- Atom = Smallest unit of an element that retains its properties
- Atom is electrically neutral → protons = electrons
🔹 2. Subatomic Particles (VERY IMPORTANT)
| Particle | Charge | Mass | Location |
|---|---|---|---|
| Proton | +1 | 1 amu | Nucleus |
| Neutron | 0 | 1 amu | Nucleus |
| Electron | –1 | ~0 | Shells |
👉 MCQ traps:
- Proton determines element identity
- Electron determines chemical behavior
- Neutron affects mass only
🔹 3. Atomic Number & Mass Number
- Atomic number (Z) = Number of protons
- Mass number (A) = Protons + Neutrons
👉 Formula:
- Neutrons = A – Z
👉 MCQ:
- Change in proton → new element
🔹 4. Isotopes, Isobars, Ions
Isotopes
- Same element, different neutrons
- Example: C-12, C-14
👉 Used in radioactivity & medicine
Isobars
- Same mass number, different elements
Ions
- Loss/gain of electrons
- Cation (+), Anion (–)
Energy and its Procurement: Structure of the Atom and Radioactivity
🔹 5. Atomic Models (VERY IMPORTANT MCQs)
Dalton Model
- Atom indivisible (❌ wrong now)
Thomson Model
- “Plum pudding model”
- Electron embedded in positive sphere
Rutherford Model
- Nucleus discovered
- Atom mostly empty space
- Gold foil experiment
👉 MCQ:
- Foil used → Gold
Bohr Model
- Electrons move in fixed energy levels (shells)
🔹 6. Electron Shells & Configuration
- Shells: K, L, M, N
- Max electrons = 2n²
👉 Examples:
- K = 2
- L = 8
- M = 18
👉 Stability:
- Outer shell = 8 electrons (octet rule)
🔹 7. Important Discoveries
| Scientist | Discovery |
|---|---|
| J.J. Thomson | Electron |
| Rutherford | Nucleus |
| Chadwick | Neutron |
👉 MCQ:
- Neutron discovered by Chadwick
☢️ RADIOACTIVITY (MCQs Notes)
🔹 8. Definition
- Radioactivity = Spontaneous emission of radiation from unstable nucleus
🔹 9. Types of Radiation (VERY IMPORTANT)
| Radiation | Charge | Penetration | Nature |
|---|---|---|---|
| Alpha (α) | +2 | Low | Helium nucleus |
| Beta (β) | –1 | Medium | Electron |
| Gamma (γ) | 0 | High | Electromagnetic wave |
👉 MCQ traps:
- Most penetrating → Gamma
- Most ionizing → Alpha
🔹 10. Radioactive Decay
- Unstable nucleus → emits radiation → becomes stable
👉 Types:
- Alpha decay
- Beta decay
- Gamma emission
🔹 11. Half-Life (VERY IMPORTANT)
- Time for half of substance to decay
👉 Key points:
- Constant for each element
- Independent of temperature & pressure
🔹 12. Nuclear Reactions
Fission
- Splitting of heavy nucleus (Uranium)
- Used in nuclear reactors
Fusion
- Combining light nuclei
- Occurs in Sun
👉 MCQ:
- Sun energy → Fusion
🔹 13. Uses of Radioactivity
- Medicine (cancer treatment)
- Carbon dating
- Power generation
- Industry
🔹 14. Hazards of Radiation
- Cancer
- Genetic mutations
- Tissue damage
🔥 MOST REPEATED MCQ POINTS
- Atom neutral → protons = electrons
- Nucleus contains → protons + neutrons
- Electron mass negligible
- Gold foil → Rutherford
- Neutron → Chadwick
- Atomic number = protons
- Isotopes → same element
- Gamma rays → highest penetration
- Alpha → highest ionization
- Half-life → constant
🎯 SUPER QUICK REVISION (1-Minute)
- Atom = proton + neutron (nucleus) + electron
- Proton → identity
- Neutron → mass
- Electron → reactions
- Isotopes → same Z, different A
- Alpha (+), Beta (–), Gamma (0)
- Gamma → most penetrating
- Half-life → fixed
- Fusion → Sun
- Fission → nuclear reactors
🔬 STRUCTURE OF ATOM MCQs (1–50)
🔹 Basic & Subatomic Particles
- Who discovered the electron?
A) Rutherford
B) Chadwick
C) J.J. Thomson ✅
D) Bohr - Proton has charge:
A) –1
B) 0
C) +1 ✅
D) +2 - Neutron has charge:
A) +1
B) –1
C) 0 ✅
D) +2 - Electron is located in:
A) Nucleus
B) Orbit/shell ✅
C) Proton
D) Core - Mass of electron is:
A) Equal to proton
B) Negligible ✅
C) Double
D) Zero - Nucleus contains:
A) Electrons
B) Protons & neutrons ✅
C) Only neutrons
D) Only protons - Atomic number represents:
A) Neutrons
B) Electrons
C) Protons ✅
D) Ions - Mass number equals:
A) p + e
B) p + n ✅
C) n + e
D) e only - Number of neutrons =
A) Z – A
B) A – Z ✅
C) A + Z
D) Z² - Atom is neutral because:
A) No charge
B) p = e ✅
C) n = p
D) e = n
🔹 Atomic Models
- Dalton model states atom is:
A) Divisible
B) Indivisible ✅
C) Charged
D) Hollow - Thomson model is called:
A) Nuclear
B) Solar
C) Plum pudding ✅
D) Quantum - Rutherford experiment used:
A) Silver foil
B) Gold foil ✅
C) Copper foil
D) Iron foil - Rutherford discovered:
A) Electron
B) Neutron
C) Nucleus ✅
D) Proton - Most of atom is:
A) Solid
B) Empty space ✅
C) Liquid
D) Gas - Bohr model explains:
A) Nucleus
B) Fixed energy levels ✅
C) Electrons at rest
D) Proton motion - Electrons revolve in:
A) Random paths
B) Fixed orbits ✅
C) Nucleus
D) Core - Energy levels are:
A) Continuous
B) Quantized ✅
C) Infinite
D) Random
🔹 Isotopes, Ions
- Isotopes have:
A) Same mass
B) Same protons ✅
C) Same neutrons
D) Same ions - Isobars have:
A) Same atomic number
B) Same mass number ✅
C) Same element
D) Same electrons - Ion is formed by:
A) Proton change
B) Electron gain/loss ✅
C) Neutron change
D) Mass change - Cation is:
A) Negative
B) Positive ✅
C) Neutral
D) Gas - Anion is:
A) Positive
B) Negative ✅
C) Neutral
D) Solid - Changing protons gives:
A) Isotope
B) New element ✅
C) Ion
D) Compound
🔹 Electron Configuration
- Max electrons in shell =
A) n²
B) 2n² ✅
C) n³
D) 2n - K shell holds:
A) 8
B) 2 ✅
C) 18
D) 32 - L shell holds:
A) 2
B) 8 ✅
C) 18
D) 32 - Octet rule means:
A) 2 electrons
B) 8 electrons ✅
C) 18 electrons
D) 32 electrons - Valence electrons are:
A) Inner shell
B) Outer shell ✅
C) Nucleus
D) Core - Chemical properties depend on:
A) Neutrons
B) Protons
C) Electrons ✅
D) Mass
🔹 Scientists
- Neutron discovered by:
A) Thomson
B) Rutherford
C) Chadwick ✅
D) Bohr - Proton discovered by:
A) Rutherford ✅
B) Chadwick
C) Thomson
D) Dalton - Bohr introduced:
A) Nucleus
B) Energy levels ✅
C) Electron
D) Neutron - Thomson used:
A) Alpha rays
B) Cathode rays ✅
C) Gamma rays
D) Beta rays
🔹 Miscellaneous
- Atomic mass unit (amu) measures:
A) Charge
B) Mass ✅
C) Volume
D) Density - 1 amu equals:
A) Proton mass approx ✅
B) Electron mass
C) Neutron charge
D) Ion - Relative atomic mass depends on:
A) Isotopes ✅
B) Ions
C) Shells
D) Charge - Period number shows:
A) Protons
B) Shells ✅
C) Neutrons
D) Charge - Group number shows:
A) Neutrons
B) Valence electrons ✅
C) Shells
D) Mass - Atom size mostly due to:
A) Nucleus
B) Electron cloud ✅
C) Proton
D) Neutron
☢️ RADIOACTIVITY MCQs (51–100)
🔹 Basic Concepts
- Radioactivity is:
A) Artificial
B) Spontaneous emission ✅
C) Controlled reaction
D) Heat - Radioactivity occurs in:
A) Stable atoms
B) Unstable nuclei ✅
C) Electrons
D) Molecules - Discovered by:
A) Rutherford
B) Becquerel ✅
C) Thomson
D) Bohr
🔹 Types of Radiation
- Alpha particle charge:
A) –1
B) +1
C) +2 ✅
D) 0 - Beta particle is:
A) Proton
B) Electron ✅
C) Neutron
D) Photon - Gamma rays are:
A) Particles
B) Waves ✅
C) Ions
D) Neutrons - Most penetrating:
A) Alpha
B) Beta
C) Gamma ✅
D) Proton - Least penetrating:
A) Alpha ✅
B) Beta
C) Gamma
D) Neutron - Most ionizing:
A) Gamma
B) Beta
C) Alpha ✅
D) Proton
🔹 Nuclear Reactions
- Fission is:
A) Joining
B) Splitting nucleus ✅
C) Heating
D) Cooling - Fusion is:
A) Splitting
B) Joining nuclei ✅
C) Ionization
D) Radiation - Sun produces energy by:
A) Fission
B) Fusion ✅
C) Combustion
D) Decay - Nuclear reactor uses:
A) Fusion
B) Fission ✅
C) Combustion
D) Evaporation
🔹 Half-Life
- Half-life is:
A) Total decay
B) Half decay time ✅
C) Full decay
D) Reaction time - Half-life depends on:
A) Temperature
B) Pressure
C) Nature of element ✅
D) Volume - Half-life is:
A) Variable
B) Constant ✅
C) Increasing
D) Decreasing
🔹 Effects & Uses
- Radiation causes:
A) Cooling
B) Mutation ✅
C) Growth
D) Expansion - Used in cancer treatment:
A) Alpha
B) Beta
C) Gamma ✅
D) Proton - Carbon dating uses:
A) C-12
B) C-14 ✅
C) O-16
D) H-1 - Nuclear energy advantage:
A) Low output
B) High output ✅
C) No waste
D) No risk
🔹 Decay Changes
- Alpha decay reduces mass by:
A) 1
B) 2
C) 4 ✅
D) 8 - Beta decay changes:
A) Mass
B) Atomic number ✅
C) Charge
D) Volume - Gamma decay changes:
A) Mass
B) Charge
C) Energy only ✅
D) Size
🔹 Miscellaneous
- Uranium is:
A) Stable
B) Radioactive ✅
C) Gas
D) Liquid - Radioactive waste is:
A) Safe
B) Dangerous ✅
C) Useful
D) Edible - Nuclear force is:
A) Weak
B) Strong ✅
C) Magnetic
D) Electric - Radiation unit:
A) Joule
B) Sievert ✅
C) Watt
D) Volt - Gamma rays are:
A) Charged
B) Neutral ✅
C) Positive
D) Negative - Alpha particle is:
A) Helium nucleus ✅
B) Electron
C) Photon
D) Proton - Beta rays deflected by:
A) Electric field ✅
B) Gravity
C) Heat
D) Sound
🔹 Final Quick MCQs
- Most dangerous radiation:
A) Alpha
B) Gamma ✅
C) Beta
D) Proton - Shielding for gamma:
A) Paper
B) Lead ✅
C) Wood
D) Plastic - Shielding for alpha:
A) Paper ✅
B) Lead
C) Steel
D) Glass - Stability depends on:
A) Neutron-proton ratio ✅
B) Electrons
C) Charge
D) Mass - Radioactive decay is:
A) Artificial
B) Natural ✅
C) Forced
D) Chemical - Radiation detected by:
A) Thermometer
B) Geiger counter ✅
C) Barometer
D) Voltmeter - Beta decay emits:
A) Proton
B) Electron ✅
C) Neutron
D) Photon - Fusion requires:
A) Low temp
B) High temp ✅
C) Pressure only
D) Water - Fission produces:
A) Small energy
B) Large energy ✅
C) No energy
D) Heat only - Nuclear energy source:
A) Coal
B) Uranium ✅
C) Gas
D) Oil - Radioactivity leads to:
A) Stability
B) Decay to stable nucleus ✅
C) Growth
D) Reaction - Isotopes used in:
A) Medicine ✅
B) Cooking
C) Painting
D) Farming - Alpha particles stopped by:
A) Air few cm ✅
B) Lead
C) Steel
D) Glass - Gamma rays travel at:
A) Sound speed
B) Light speed ✅
C) Slow
D) Variable - Nuclear energy is:
A) Chemical
B) Atomic nucleus energy ✅
C) Heat
D) Light - Beta particles have:
A) Positive charge
B) Negative charge ✅
C) Neutral
D) Double charge - Radioactivity discovered in:
A) 1896 ✅
B) 1900
C) 1910
D) 1920 - Alpha particles are:
A) Heavy ✅
B) Light
C) Neutral
D) Waves - Nuclear reactions involve:
A) Electrons
B) Nucleus ✅
C) Molecules
D) Ions - Final aim of decay:
A) Instability
B) Stability ✅
C) Growth
D) Energy loss
🎯 Exam Tip
Focus heavily on:
- Scientists & discoveries
- Alpha, beta, gamma differences
- Atomic number & mass number
- Decay rules (alpha ↓4 mass, ↓2 Z)