ATOMIC STRUCTURE & NUCLEAR CONCEPTS
Fundamental Subatomic Particles
Ordinary Hydrogen (Protium, ¹H₁) is the only atom that has no neutron in its nucleus.
Atomic Number & Mass Number
Standard Element Representation: ᴬZ X (where A = Mass Number at top, Z = Atomic Number at bottom)
- Atomic Number (Z): Number of protons in the nucleus. In a neutral atom, Number of Protons = Number of Electrons = Z. It determines the element’s position in the periodic table.
- Mass Number (A): Total number of nucleons (Protons + Neutrons). Formula: A = Z + N
- Neutron Calculation Formula: Number of Neutrons (N) = Mass Number (A) – Atomic Number (Z)
Isotopes, Isobars, and Isotones (Comparison Table)
| Term | Definition | Memory Trick | Important Exam Examples |
| Isotopes | Same Atomic Number (Z), different Mass Number (A). Same chemical properties. | Ends in ‘P’ → Same Protons | • Protium (¹₁H), Deuterium (²₁H), Tritium (³₁H) • Carbon: ¹²₆C, ¹⁴₆C • Chlorine: ³⁵₁₇Cl, ³⁷₁₇Cl |
| Isobars | Same Mass Number (A), different Atomic Number (Z). Different chemical properties. | Contains ‘A’ → Same Mass Number (A) | • ⁴⁰₁₈Ar, ⁴⁰₁₉K, ⁴⁰₂₀Ca (All have Mass = 40) • ¹⁴₆C and ¹⁴₇N (Both have Mass = 14) |
| Isotones | Same number of Neutrons (N = A – Z), different Atomic & Mass Numbers. | Ends in ‘N’ → Same Neutrons | • ¹⁴₆C (14 – 6 = 8) & ¹⁶₈O (16 – 8 = 8) • ³₁H (3 – 1 = 2) & ⁴₂He (4 – 2 = 2) |
IMPORTANT FACTS:
Chemical vs Physical Behavior: Isotopes have identical chemical properties (same electron configuration), but differ in physical properties (density, boiling point, mass).
Heavy Water (D₂O): Oxide of Deuterium (²H), extensively used as a moderator and coolant in nuclear reactors.
Radioactive Hydrogen: Tritium (³₁H) is the only natural radioactive isotope of hydrogen (emits low-energy β particles).
Carbon Dating (Carbon-14): Used by archaeologists to determine the age of ancient organic materials, wood, and fossils.
Cobalt-60 (⁶⁰Co): Emits gamma rays; used widely in radiation therapy for cancer treatment.
Iodine-131 (¹³¹I): Used in nuclear medicine for diagnosing and treating thyroid gland disorders (e.g., Goitre).
Uranium-235 (²³⁵U): Used as a fissile fuel in nuclear reactors and atomic energy generation.