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.