Lecture Notes: Nuclide Symbols

Structure of Atoms

• Atoms consist of:
  • Nucleus: Contains protons (positively charged) and neutrons (no charge).
  • Electrons: Negatively charged and are located some distance from the nucleus.

Elements and Atomic Number

• An element is determined by the number of protons in an atom.
  • Atomic Number: Number of protons in the nucleus (defines the element).
  • Examples:
    • 1 proton = Hydrogen
    • 2 protons = Helium
    • 3 protons = Lithium

Mass Number

• Mass Number: Sum of protons and neutrons in the nucleus.
  • Only protons contribute to the atomic number, but both protons and neutrons contribute to the mass number.
  • Protons and neutrons each have about 1 atomic mass unit; electrons are negligible in mass.
  • Example: Carbon-12 has 6 protons and 6 neutrons.

Nuclide Symbols

• Represent an atom using nuclide symbols:
  • Abbreviation of the element with one or two letters (first letter capitalized).
  • Bottom Left: Sometimes includes the atomic number.
  • Upper Left: Mass number (important for identifying isotopes).
  • Upper Right: Charge, if the atom is an ion.

Isotopes and Ions

• Isotopes: Atoms of the same element with different numbers of neutrons.
  • Mass number = Protons + Neutrons
  • Neutrons = Mass number - Atomic number
• Ions: Atoms with an electrical charge due to differing numbers of protons and electrons.
  • Gain an electron = -1 charge
  • Lose an electron = +1 charge

Periodic Table and Atomic Mass

• Elements are arranged by atomic number on the periodic table.
• Atomic Masses: Not whole numbers because they are averages of isotopic masses.
  • Consider relative abundance of isotopes.
  • Example: Chlorine has isotopes Cl-35 and Cl-37.
    • 75% Cl-35, 25% Cl-37
    • Atomic mass reflects the weighted average.

Key Concepts

• Different protons = Different elements
• Different neutrons = Different isotopes
• Different electrons = Different ions

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