Overview
This lecture covers units of measurement in chemistry, focusing on SI units, derived units, and essential metric prefixes.
SI Base Units
- All scientific measurements require both a number and a unit for clarity.
- The SI system (International System of Units) uses seven base units: kilogram (mass), meter (length), second (time), kelvin (temperature), ampere (electric current), mole (amount of substance), and candela (luminous intensity).
- The base unit for mass (kilogram) uniquely includes a metric prefix.
Derived Units
- Derived units are formed by combining base units.
- Common derived units include density (mass/volume), velocity (length/time), and volume (length³).
- Volume can be expressed as cubic centimeters (cm³), which equals one milliliter (mL).
- The joule (unit of energy) is defined as kilogram·meter²/second² (kg·m²/s²).
Metric Prefixes
- Metric prefixes modify base or derived units to represent larger or smaller quantities.
- Key prefixes to learn: kilo (k, 10³), centi (c, 10⁻²), milli (m, 10⁻³), micro (μ, 10⁻⁶), and nano (n, 10⁻⁹).
- Prefixes are placed before units, e.g., 1 kilogram (kg) equals 1,000 grams (g).
- Units and prefixes have standard abbreviations, such as ms for millisecond or ng for nanogram.
Example Conversions
- 1 kilogram = 1,000 grams
- 10 seconds = 10 s
- 10 cubic centimeters (cc or cm³) = 0.01 liter (L)
- 0.345 micrograms = 0.000000345 grams
Key Terms & Definitions
- SI Unit — Internationally accepted standard unit for measurement.
- Base Unit — Fundamental unit in the SI system.
- Derived Unit — Unit made by combining base units.
- Metric Prefix — Symbol added to a unit to indicate a power of ten multiple.
Action Items / Next Steps
- Memorize SI base units and key metric prefixes (kilo, centi, milli, micro, nano).