Understanding Units and Atomic Theory

Sep 17, 2024

Lecture Notes: Units, Conversion, and Atomic Theory

Introduction

  • Challenges with technology, particularly the projector.
  • Discussing dimensional analysis and conversion of units.

Dimensional Analysis

  • Conversion Example:
    • Converting 17.5 cm to meters:
      • 1 cm = 10^-2 m.
      • Different ways of expressing conversions (e.g., dividing units cancels them).
  • Example:
    • x times x = x².
    • x³ divided by x = x².

Conversion Example: Volume

  • Problem: Convert 6.83 m³ to milliliters.
    • Use conversion: 1 cm³ = 1 mL.
    • Convert m³ to cm³ using: 1 m³ = 1000000 cm³.
    • Result: 6.83 x 10^6 mL.

Units and Mathematical Operations

  • Multiplying units increases power; dividing decreases power.
  • Addition and subtraction don't cancel units, they factor them.

Density and Units

  • Density = mass/volume (e.g., g/mL). Units do not cancel out.

Formation of Elements

  • Elements formed during the Big Bang.
  • Fundamental particles formed: protons, neutrons.
  • Stars fuse elements (e.g., hydrogen atoms form helium).

Dalton's Atomic Theory

  • Elements made of tiny particles: atoms.
  • Atoms cannot be created/destroyed.
  • All atoms of an element are identical (mostly true).
  • Atoms of different elements are different.
  • Atoms combine to form compounds.

Law of Multiple Proportions

  • Elements combine in whole number ratios (e.g., CO and CO₂).
  • Mass ratios reflect these combinations.

Structure of Atoms

  • Atoms consist of a nucleus and electron cloud.
  • Nucleus:
    • Contains protons (+ charge) and neutrons (neutral).
  • Electron Cloud:
    • Contains electrons (- charge).

Rutherford's Experiment

  • Tested the plum pudding model.
  • Most alpha particles passed through gold foil, indicating empty space.
  • Small positive charge concentrated in the nucleus.

Conclusion

  • Atomic theory continues to develop; understanding of units and conversions critical for chemistry.
  • Prepare for next class: read Chapter 2 and print activity sheet.