Chemistry units
Within chemistry, precise measurement is essential, and units of measurement are used to quantify a wide range of physical properties. The International System of Units (SI) is the globally recognized standard, providing a consistent set of units for scientific measurements. This system is structured around base units, which form the foundational elements upon which all other units are derived.
1. Base Units (SI Units)
These are the fundamental units defined by the International System of Units (SI):
| Quantity | Unit Name | Symbol |
|---|---|---|
| Length | meter | m |
| Mass | kilogram | kg |
| Time | second | s |
| Temperature | kelvin | K |
| Amount of substance | mole | mol |
| Electric current | ampere | A |
| Luminous intensity | candela | cd |
Mole is especially important in chemistry—it represents 6.02214076 × 1023 mol−1 particles (Avogadro’s number).
2. Derived Units
These are combinations of base units used to express more complex quantities:
| Quantity | Derived Unit | Symbol |
|---|---|---|
| Volume | cubic meter | m3 |
| Density | kilogram per cubic meter | kg/m3 |
| Pressure | pascal | Pa |
| Energy | joule | J |
| Concentration | mole per liter | mol/L |
| Speed | meter per second | m/s |
Concentration is often expressed in molarity (M), which is mol/L.
3. Common Laboratory Units
In practice, chemists often use more convenient units:
- Mass: grams (g), milligrams (mg)
- Volume: liters (L), milliliters (mL)
- Temperature: degrees Celsius (°C)
- Pressure: atmospheres (atm), torr, mmHg, bar
- Energy: calories (cal), kilojoules (kJ)
4. Atomic and Molecular Units
Used in theoretical and quantum chemistry:
- Atomic mass unit (amu or u): used to express atomic and molecular weights
- Angstrom (Å): unit of length for atomic scales, 1.0 × 10-10 meters
- Electronvolt (eV): unit of energy in atomic physics
Why Units Matter
- They allow accurate calculations in chemical reactions.
- They help compare results across labs and countries.
- They ensure safety in handling chemicals and equipment.