Atoms & Isotopes – Quick Review

Atomic structure and isotopes

  • Atom components: nucleus (protons p+, neutrons n0) and electron cloud (electrons e-)
  • Neutral atom: number of electrons equals number of protons
  • Key counts:
    • Z = \text{# protons}
    • N = \text{# neutrons}
    • A=Z+NA = Z + N
  • Example: Helium-4
    • Z=2,N=2,A=4Z = 2, N = 2, A = 4
    • For a neutral atom: Ne=Z=2N_e = Z = 2

Isotopes

  • Isotopes have the same ZZ but different NN
  • Hydrogen isotopes: protium (1H, Z=1,N=0,A=1Z=1, N=0, A=1), deuterium (2H, Z=1,N=1,A=2Z=1, N=1, A=2), tritium (3H, Z=1,N=2,A=3Z=1, N=2, A=3)
  • Carbon-13 example: Z=6,N=7,A=13Z=6, N=7, A=13; notation: A<em>ZX^{A}<em>{Z}X (e.g., 13</em>6C^{13}</em>{6}C)
  • Transcript example: "six protons, seven neutrons" corresponds to Z=6,N=7,A=13Z=6, N=7, A=13 (carbon-13)

Quick recap

  • Protons define the element; neutrons vary to form isotopes; electrons balance protons in neutral atoms
  • Notation and basic relations: A=Z+NA = Z + N, Ne=ZN_e = Z for neutral atoms