Understanding Atomic Structure and Composition

Sep 4, 2024

Atomic Structure and Symbolism

Learning Objectives

  • Understand the scale and structure of the atom
  • Learn about the charge and mass of subatomic particles
  • Define atomic number and mass number
  • Differentiate between ions and neutral atoms
  • Recognize chemical symbols and isotopes

Atomic Size and Structure

  • Size of Atoms and Nucleus
    • Atoms: ~10^-10 meters in diameter
    • Nucleus: ~10^-15 meters
    • Analogy: If an atom is a football stadium, the nucleus is a blueberry
  • Mass and Composition
    • Most mass in nucleus (protons and neutrons)
    • Electrons: Move around the nucleus, significantly lighter

Fundamental Units

  • Charge
    • Fundamental unit of charge, E: 1.602 x 10^-19 coulombs
    • Electron: -1 charge, Proton: +1 charge, Neutron: no charge
  • Mass
    • Atomic Mass Unit (amu): based on 1/12 of a carbon-12 atom
    • 1 amu = 1.6605 x 10^-24 grams
    • Masses:
      • Electron: 0.00055 amu
      • Proton: 1.0073 amu
      • Neutron: 1.0083 amu

Atomic Number and Mass Number

  • Atomic Number (Z)
    • Number of protons in an atom
    • Defines the chemical element (e.g., Carbon has Z=6)
  • Mass Number (A)
    • Total number of protons and neutrons
    • Neutrons = Mass Number - Atomic Number

Ions and Neutral Atoms

  • Neutral Atoms
    • Equal number of protons and electrons
  • Ions
    • Charge = Protons - Electrons
    • Cations: Positive charge (more protons)
    • Anions: Negative charge (more electrons)
    • Examples:
      • Sodium (Na): Loses an electron → Cation
      • Oxygen (O): Gains two electrons → Anion

Chemical Symbols

  • Abbreviations for elements
    • Example: Aluminum (Al), Lead (Pb)
  • Symbols: 1 or 2 letters, sometimes 3 for recent elements
  • Representation:
    • Element symbol with mass number (superscript) and atomic number (subscript)
    • Charge shown as superscript (if ionized)

Isotopes

  • Atoms of the same element with different mass numbers
  • Example: Hydrogen isotopes
  • Atomic Mass Calculation
    • Weighted average of isotopes
    • Example: Boron calculation
    • Formula: Sum of (fractional abundance x mass of isotope)

Mass Spectrometry

  • Purpose: Determine natural abundances of isotopes
  • Process
    • Sample vaporized and ionized
    • Ions separated by mass and charge
    • Mass spectrum graph generated, showing isotope peaks (e.g., for Zirconium)