Fundamentals of Atoms and Isotopes

Sep 6, 2024

Lecture Notes on Atoms and Elements

Introduction to Atomic Theory

  • Dalton's Atomic Theory (Early 1800s)
    • Key Points: All matter is made of atoms; atoms are indivisible and indestructible.
    • Correction: Atoms can be divided into subatomic particles (electrons, protons, neutrons).
    • Isotopes: Atoms of the same element can differ in mass and properties due to the existence of isotopes.

Dalton's Atomic Theory Detailed

  1. All matter is made of atoms: True.
  2. Atoms are indivisible and indestructible: Incorrect, can be broken down further.
  3. All atoms of a given element are identical: Incorrect, due to isotopes.
  4. Compounds are combinations of different elements: True.
  5. Chemical reactions are the rearrangement of atoms: True.

Discovery of Subatomic Particles

  • Electron (Around 1900): First discovered subatomic particle, part of the atom, negatively charged.
  • Protons and Neutrons: Found in the nucleus, protons are positively charged, neutrons are neutral.

Alpha Scattering Experiment (1910)

  • Purpose: Test the plum pudding model (positive charge spread out with electrons embedded).
  • Result: Disproved the model, leading to the discovery of the nucleus.
  • Nucleus: Dense central core, contains protons and neutrons.

Structure of the Atom

  • Nucleus: Contains protons and neutrons, dense.
  • Electrons: Negatively charged, orbit the nucleus.
  • Mass and Charge:
    • Electrons are much lighter (~1/1000 of a proton's mass).
    • Most of the atom's mass is in the nucleus.
    • Atoms are mostly empty space.

Isotopes

  • Definition: Atoms of the same element with different numbers of neutrons.
  • Example: Carbon-12 vs Carbon-13.
  • Mass Number (A): Sum of protons and neutrons.
  • Atomic Number (Z): Number of protons.
  • Notation: ( \text{Element}^{A}_{Z} )

Atomic Mass and Units

  • Atomic Mass Unit (amu): Defined as 1/12 of the mass of ( ^{12}C ).
  • Weighted Average: Used to calculate the atomic mass based on natural isotopic abundance.
  • Calculations:
    • Weighted average example with carbon isotopes.
    • Calculation for naturally occurring elements reflects periodic table values.

Key Concepts Review

  • Protons define the element.
  • Electrons determine chemical behavior.
  • Isotopes affect atomic mass.
  • Periodic Table Mass: Reflects weighted average of isotopic masses.

Conclusion

  • Understanding the structure of atoms, isotope distribution, and atomic mass is crucial for comprehending chemical behavior and properties of elements.