Class 9 Exam > Class 9 Notes > Science Class 9 > Mnemonics : Structure of the Atom
Mnemonics : Structure of the Atom | Science Class 9 PDF Download
1. Subatomic Particles
Mnemonic: PEN
Sentence: “A PEN writes the story of an atom.”
Mnemonic Explanation:
P = Proton → +ve charge → in nucleus
E = Electron → –ve charge → orbits around
N = Neutron → 0 charge → in nucleus
2. Scientists and Subatomic Particles Discoveries
Mnemonic: “Thomson's Electron Gold's Proton Bohr's Shell James Neutron”
Mnemonic Explanation:
Thomson (1897) → Electron
Goldstein (1886) → Canal Rays/Proton
Bohr (1913) → Electron shells
James Chadwick (1932) → Neutron
3. Rutherford’s Gold Foil Experiment
Mnemonic: “Most Passed, Few Deflected, One Reflected”
Mnemonic Explanation:
Most α-particles passed → atom is mostly empty
Some deflected → positive center (nucleus)
One bounced back → dense nucleus
4. Valency
Mnemonic: “VALENCE = Value of Electrons in Chemical Reactions"
Mnemonic Explanation: Valency = number of electrons gained, lost, or shared to complete octet
5. First 20 Elements of Periodic Table
Mnemonic For First 10 Elements: “Hi Hello Listen B B C News On Friday Night "
Mnemonic For 11-20 Atomic No. Elements : " Naa Maango Allah Se Pepsi Soda Cola Aur Kaju Catli"
Mnemonic Explanation
H– Hydrogen (1)
He – Helium (2)
Li – Lithium (3)
Be – Beryllium (4)
B – Boron (5)
C – Carbon (6)
N – Nitrogen (7)
O – Oxygen (8)
F – Fluorine (9)
Ne – Neon (10)
Na – Sodium (11)
Mg – Magnesium (12)
Al – Aluminium (13)
Si – Silicon (14)
P – Phosphorus (15)
S – Sulfur (16)
Cl – Chlorine (17)
Ar – Argon (18)
K – Potassium (19)
Ca – Calcium (20)
6. Isotopes vs. Isobars vs. Isotones
Mnemonic: “Top-Bar-Tone”
Mnemonic Explanation:
ISOtopes → Same Atomic Number (Z)
“TOP = same top (Z), different bottoms (mass)”ISObars → Same Mass Number (A)
“BAR = balanced mass bars, different Z”ISOtones → Same Number of Neutrons
“TONE = same NEUTRONS”
Examples:
Isotopes: ¹H, ²H, ³H
Isobars: ⁴⁰Ar (Z=18), ⁴⁰Ca (Z=20)
Isotones: ¹²C₆ and ¹⁶O₈ → both have 8 neutrons
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FAQs on Mnemonics : Structure of the Atom - Science Class 9
| 1. What are subatomic particles and what roles do they play in an atom? |  |
Ans. Subatomic particles are the fundamental constituents of atoms, which include protons, neutrons, and electrons. Protons are positively charged and reside in the nucleus, neutrons are neutral and also found in the nucleus, while electrons are negatively charged and orbit the nucleus. Together, these particles determine the chemical behavior and identity of an element.
| 2. Who were the key scientists involved in the discovery of subatomic particles? | |
Ans. Some key scientists include J.J. Thomson, who discovered the electron, Ernest Rutherford, who identified the nucleus through his gold foil experiment, and James Chadwick, who discovered the neutron. Their collective work laid the foundation for modern atomic theory and our understanding of atomic structure.
| 3. What was the significance of Rutherford's Gold Foil Experiment? | |
Ans. Rutherford's Gold Foil Experiment, conducted in 1909, was significant because it revealed that atoms consist mostly of empty space with a dense, positively charged nucleus at the center. This challenged the existing plum pudding model and led to the development of the nuclear model of the atom, providing key insights into atomic structure.
| 4. What is valency and how is it determined? | |
Ans. Valency is the measure of an atom's ability to bond with other atoms and is determined by the number of electrons in its outer shell. Atoms tend to bond in ways that allow them to achieve a full outer shell, typically following the octet rule for stability. Elements with similar valency often form similar types of chemical bonds.
| 5. What are the differences between isotopes, isobars, and isotones? | |
Ans. Isotopes are variants of an element that have the same number of protons but different numbers of neutrons. Isobars are different elements that have the same mass number but different atomic numbers. Isotones are atoms that have the same number of neutrons but different numbers of protons. Each concept highlights different aspects of atomic structure and behavior.
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