The Metric System

The metric system is based on a set of units of measurement, with prefixes that denote powers of 10.

There are 7 fundamental “base” units:

· meter (m): length

· kilogram (kg): mass (even though “kilo” is actually a prefix, mass is defined based on the kilogram, not the gram)

· second (s): time

· Kelvin (K): temperature

· mole (mol): amount of substance

· ampere (A): electric current

· candela (cd): intensity of light

Each of these base units is defined by conditions that could be duplicated in a laboratory anywhere in the world (except for the kilogram, which is defined by a physical object).  All other metric units are combinations of one or more of these seven.

The metric system uses prefixes to indicate multiplying a unit by a power of ten.  There are prefixes for powers of ten from 10⁻¹⁸ to 10¹⁸ but in chemistry, only the following four are commonly used:

· kilo (k) = 10³ = 1000

· centi (c) = 10⁻² =  = 0.01

· milli (m) = 10⁻³ =  = 0.001

· micro (μ) = 10⁻⁶ =  = 0.000 001

These prefixes can be used with any metric unit.  For example, if a mole is 6.02 × 10²³ objects, a millimole would be 6.02 × 10²⁰ objects.