CHEM 105 - Chapter 1 Notes

Chapter 1: Introduction to Chemistry

Measurement

  • Measurement requires both a number and a unit.
  • Units are essential for a complete and correct answer in chemistry problems.
Metric System
  • Scientists use the metric system.
  • Four key quantities: length, mass, volume, and time.
    • Length: meter (m)
    • Mass: gram (g)
    • Volume: liter (L)
    • Time: seconds (s)
  • Chemists use notations and shorthand to represent concepts efficiently.
  • Pay attention to capitalization (e.g., L for liters).
Metric Prefixes
  • Prefixes modify base units by powers of 10.
  • Prefixes indicate whether the unit is larger or smaller than the base unit.
  • Examples:
    • Giga (G): billion (10910^9)
    • Kilo (k): 1,000 (10310^3)
    • Nano (n): one billionth (10−910^{-9})
  • Scientific notation uses exponents to represent the number of zeros.
Equivalence
  • Equivalence relates different units of measure.
  • Examples:
    • 1 foot = 12 inches
    • 1 pound = 16 ounces
    • 1 ton = 2,000 pounds
    • 2.54 centimeters = 1 inch
    • 1 liter = 1.057 quarts

Significant Figures (Sig Figs)

  • Significant figures are the numbers in a measurement that are considered reliable.
  • There are exact and inexact numbers; Sig Figs apply only to inexact numbers.
Exact Numbers
  • Exact numbers come from counting (e.g., babies, fingers, toes).
  • Exact numbers are part of a definition.
Inexact Numbers
  • Inexact numbers come from measurements.
  • All measurements have a level of uncertainty.
  • Examples: 15.3 centimeters, 0.8 grams, 0.0034 milliliters.
Rules for Sig Figs
  • All non-zero digits are significant.
    • Example: 65.2 grams (3 sig figs), 255.345 (6 sig figs).
  • Zeros between non-zero digits are significant.
    • Example: 29.05 grams (4 sig figs).
  • Zeros at the end of a number with a decimal place are significant.
    • Example: 3.7500 centimeters (5 sig figs).
  • Leading zeros are not significant (they are placeholders).
    • Example: 0.00245 (3 sig figs).
  • Trailing zeros in a number without a decimal place are not significant.
    • Example: 2570 meters (3 sig figs).
Math with Sig Figs
  • Multiplication and division: the answer must have the lowest number of sig figs of any of the numbers being multiplied or divided.
  • Addition and subtraction: consider decimal places.