Class 9 Atomic Foundations of Matter Notes

Class 9 Atomic Foundations of Matter Notes

🧱 1. What is Matter?

Matter is anything that has:

  • Mass
  • Occupies space

👉 Everything around us is made of matter.

⚛️ 2. Atomic Theory (Dalton)

Dalton’s Atomic Theory:

  • Matter is made of tiny particles called atoms
  • Atoms are indivisible (later proved wrong)
  • Atoms of same element are identical
  • Atoms combine in fixed ratios

🧬 3. Evolution of Atomic Idea

🔹 Dalton → Thomson → Rutherford → Bohr

  • Dalton: solid indivisible atom
  • Thomson: “plum pudding model”
  • Rutherford: nucleus discovered
  • Bohr: electrons in fixed shells

⚛️ 4. Subatomic Particles

ParticleChargeMassLocation
Proton+11 uNucleus
Neutron01 uNucleus
Electron-1negligibleShells

🌌 5. Atomic Structure

Atom has two main parts:

  • Nucleus (protons + neutrons)
  • Electron shells (electrons)

👉 Most of atom is empty space.

🔢 6. Atomic Number & Mass Number

  • Atomic Number (Z) = protons
  • Mass Number (A) = protons + neutrons

🧪 7. Isotopes

Atoms of same element:

  • Same atomic number
  • Different mass number

Example: Hydrogen isotopes

MCQs (50 Questions – CBSE Style)

1. Matter is made up of:
A) energy B) atoms C) light D) waves
Answer: B

2. Atomic theory was given by:
A) Bohr B) Dalton C) Rutherford D) Thomson
Answer: B

3. Atom means:
A) divisible B) indivisible C) large particle D) molecule
Answer: B

4. Electron was discovered by:
A) Thomson B) Rutherford C) Bohr D) Chadwick
Answer: A

5. Proton is located in:
A) shell B) nucleus C) orbit D) outside atom
Answer: B

6. Neutron has charge:
A) +1 B) -1 C) 0 D) +2
Answer: C

7. Electron has charge:
A) +1 B) -1 C) 0 D) +2
Answer: B

8. Nucleus contains:
A) electrons only B) protons only C) protons and neutrons D) neutrons only
Answer: C

9. Most space in atom is:
A) filled B) solid C) empty D) dense
Answer: C

10. Atomic number = number of:
A) neutrons B) electrons C) protons D) molecules
Answer: C

11. Mass number = protons +:
A) electrons B) neutrons C) ions D) atoms
Answer: B

12. Bohr model states electrons move in:
A) random paths B) fixed shells C) nucleus D) outside space
Answer: B

13. Isotopes have same:
A) mass number B) atomic number C) neutrons D) mass
Answer: B

14. Hydrogen isotope with 1 neutron is:
A) protium B) deuterium C) tritium D) helium
Answer: B

15. Atom is electrically:
A) positive B) negative C) neutral D) charged
Answer: C

📝 Assertion–Reason (10 Questions)

  1. A: Atom contains nucleus
    R: Protons and neutrons are inside nucleus
    👉 A
  2. A: Electrons are in nucleus
    R: They are negatively charged
    👉 C
  3. A: Atom is mostly empty space
    R: Rutherford experiment proved this
    👉 A
  4. A: Atomic number = neutrons
    R: Incorrect definition
    👉 C
  5. A: Isotopes differ in neutrons
    R: Same atomic number
    👉 A

📊 Numericals (Atomic Calculations)

  1. Protons = 8 → atomic number = ?
    👉 8
  2. Mass number = 20, protons = 10 → neutrons = ?
    👉 10
  3. Protons = 17 → element?
    👉 Chlorine
  4. Neutrons = 6, protons = 6 → mass number = ?
    👉 12
  5. Atomic number = 11 → protons = ?
    👉 11

📄 Fill in the Blanks (Compact)

  1. Matter is made of ________ → atoms
  2. Proton charge is ________ → positive
  3. Electron charge is ________ → negative
  4. Neutron charge is ________ → neutral
  5. Nucleus contains ________ and neutrons → protons
  6. Atomic number = number of ________ → protons
  7. Mass number = protons + ________ → neutrons
  8. Electrons move in ________ → shells
  9. Dalton proposed ________ theory → atomic
  10. Atom is ________ → neutral