Measurement - Fundamentals of Chemistry - page 41

2.3 The Metric System

The metric system and its more modern counterpart SI (for S ystème I nterna-
tional d'Unités) are systems of units designed to make calculations as easy as
possible. It was designed to make every word mean one and only one thing. Its
subdivisions and multiples of units are powers of 10 times a primary unit. Each
of its prefixes means the same thing, no matter what unit it is attached to. The
abbreviations for the quantities and prefixes are easy to remember. All these
features have been built into the metric system to make it easy. Contrast this
lack of ambiguity with the ambiguity in the English system, as illustrated in
Example 2.4.
Learning the following six words is essential to understanding the metric
system:

1. meter 4. centi-

2. gram 5. milli-

3. liter 6. kilo-

(A few more words will be added as we progress.) Meter, gram, and liter are
the units of length, mass, and volume, respectively, in the metric system. Just
as the English system has subdivisions of its primary units (12 inches [in.] in a
foot, for example), so does the metric system. But the metric system uses pre-
fixes that mean the same thing no matter what primary unit they are used with.
Centi-, milli-, and kilo- are prefixes that indicate certain multiples or divisions
of any primary unit. Other less important prefixes are given along with these in
Table 2.2.
The meter is the primary unit of length in the metric system. Its abbrevi-
ation is m. The meter is defined in such a way that it can be duplicated pre-
cisely in any well-equipped laboratory in the world. It had been defined as the
distance between two marks on a metal bar kept at the Bureau of Weights and
Measures in Paris. (It now has an even more precise definition.) A meter is 39.37
in. long—3.37 in. longer than a yard.
A standard is an agreed upon quantity with which like quantities can be
compared. For example, the meter is the agreed standard of length, to which
other lengths can be compared. In the measurement of most quantities, the

Table 2.2

Metric Prefixes*

Prefix Abbreviation Meaning

Giga- G One billion 1,000,000,000

Mega- M One million 1,000,000

Kilo- k One thousand 1000

Deci- d One-tenth 0.1

Centi- c One-hundredth 0.01

Milli- m One-thousandth 0.001

Micro- One-millionth 0.000001

Nano- n One-billionth 0.000000001

Pico- p One-trillionth 0.000000000001

*The most important prefixes for most chemistry courses are given in boldface type.