What is Isotopes ?

Definition: Isotopes are atoms of the same element that have the same atomic number (same protons) but different mass numbers (different neutrons).

Key point: Isotopes have the same chemical properties (because same electrons) but different physical properties like density, melting point, and boiling point (because different mass).

Isotopes of Hydrogen (Atomic No. = 1):

Protium (¹₁H) — Protons: 1, Neutrons: 0, Abundance: 99.985%

Deuterium (²₁H or D) — Protons: 1, Neutrons: 1, Abundance: 0.015% 

Tritium (³₁H or T) — Protons: 1, Neutrons: 2, Abundance: Very rare

Isotopes of Carbon (Atomic No. = 6):

Carbon-12 (¹²₆C) — Protons: 6, Neutrons: 6, Abundance: 98.98%

Carbon-13 (¹³₆C) — Protons: 6, Neutrons: 7, Abundance: 1.109%

Carbon-14 (¹⁴₆C) — Protons: 6, Neutrons: 8, Abundance: 1 part per trillion (very rare)

Isotopes of Chlorine (Atomic No. = 17):

Chlorine-35 (³⁵₁₇Cl) — Protons: 17, Neutrons: 18, Abundance: 75.53%

Chlorine-37 (³⁷₁₇Cl) — Protons: 17, Neutrons: 20, Abundance: 24.47%

Isotopes of Uranium (Atomic No. = 92):

Uranium-234 (²³⁴₉₂U) — Protons: 92, Neutrons: 142, Abundance: 0.05%

Uranium-235 (²³⁵₉₂U) — Protons: 92, Neutrons: 143, Abundance: 0.75%

Uranium-238 (²³⁸₉₂U) — Protons: 92, Neutrons: 146, Abundance: 99.245%