l>Lesson I: The Metric System and SI Units
|A meter is 3.37 inches more than a yard.
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|A liter is 1.82 fluid ounces more than a quart.|
|A dime weighs about one gram.|
|Metric Base UnitsThe metric system uses the following base units:Unit of MeasurementNameAbbreviation|
Frequently the above units are too small or more often too large to appropriately scale the measured quantity. It is then necessary to subdivide or expand our measurement unit. This will be discussed in the section on prefixes.
|The liter is not the SI unit of volume Volume is a unit derived from length. The volume (V) of a cube that has length (l) = 1.0 cm, width (w) = 1.0 cm, and height (h) is given by:V = l × w × h = 1.0 cm × 1.0 cm × 1.0 cm= 1.0 cm3By definition, 1.0 cm3 = 1.0 mL|
It follows from dimensional analysis that 1.0 dm3 = 1.0 L.
|Amount of Substance||Mole||mol||Electric Current||Ampere||I||Luminous Intensity||Lumen||Iv|
The SI units are used to construct all other units (these are called derived units). Some examples:
|Velocity||v||m · s-1|
|Force||F||kg · m · s-2||Newton (N)|
|Energy||E||kg · m2 · s-2||Joule (J)|
Outside the United States, the word “meter” is spelled “metre” and the word “liter” is spelled “litre.”
To change the scale of the base units, prefixes are attached. A prefix represents a factor by which the base unit must be multiplied. Metric prefixes are listed below (The prefixes most-commonly used in chemistry are listed in red):PrefixSymbolDecimalValuePower of Ten
|In addition to the base metric units, many other scientific quantities also employ this system of prefixes:||1 Mb = 1 Megabyte = 1 × 106 byte|
|1 Food Calorie = 1 kcal= 1 kilocalorie = 1 × 103 calorie|
|1 ns = 1 nanosecond = 1 × 10-9 second|
|1 pf = 1 picofarad = 1 × 10-12 farad|
|1 kWH = 1 kiloWatt·hour = 1 × 103 Watt·hour|
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