Overview
This lecture introduces common measurements in introductory chemistry—length, area, volume, mass, density, and temperature—along with their typical units and key relationships.
Length, Area, and Volume
- Length measures distance in one dimension; common units are meters, centimeters, millimeters, kilometers, or miles.
- Area is two-dimensional (plane/sheet); units include square meters or square centimeters (e.g., 10 cm × 10 cm = 100 cm²).
- Volume is three-dimensional; units include cubic centimeters (cm³), liters (L), or cubic meters (m³).
- 1,000 cm³ equals 1 liter; 1 liter equals 1,000 milliliters (mL).
- 1 cm³ is exactly equal to 1 mL; these are interchangeable.
- Do not write “mL³” or “cm³³”; the units are already three-dimensional.
Mass
- Mass measures the amount of matter (“stuff”) in an object.
- Common units are kilograms (kg), grams (g), milligrams (mg), and micrograms (μg).
- Atomic mass unit (amu) is used for very small masses, such as atoms.
- Technically, mass is the “inertial property” of matter—the more mass, the harder it is to move (F = m × a).
- Mass is related to the resistance (inertia) to acceleration (change in motion).
Density
- Density (d or ρ) is the ratio of mass to volume: d = m / V.
- Density depends on the element’s atomic mass and how closely atoms are packed (packing efficiency/crystal structure).
- Even identical volumes may have different densities based on element type and atomic arrangement.
Temperature
- Common units are Celsius (°C), Fahrenheit (°F), and Kelvin (K).
- °F = 1.8 × °C + 32; K = °C + 273.15.
- Temperature measures the strength of motion (kinetic energy) of particles, not the total thermal energy (heat).
- Thermal energy (“heat”) relates to the total amount of vibrational energy, not just temperature.
- Example: A swimming pool at low temperature can have more heat than a lit match at high temperature due to size.
Key Terms & Definitions
- Length — Measurement of distance in one dimension.
- Area — Measurement of surface in two dimensions.
- Volume — Measurement of space in three dimensions.
- Mass — Amount of matter in an object; relates to inertia.
- Density — Mass per unit volume (d = m / V).
- Temperature — Measure of the strength of particle motion; not the same as thermal energy (heat).
Action Items / Next Steps
- Review the relationships between units, especially volume (cm³, mL, L).
- Practice converting between temperature scales (°C, °F, K).
- Understand and memorize key definitions for upcoming quizzes or exams.