

Introduction
The metric system is the preferred system of scientific units for several reasons:

The terms mass and weight are often used interchangebly in chemistry. Strictly speaking, weight is the force (F) associated with a given mass (m) as it is accelerated (a) by gravity: 

Metric Base Units The metric system uses the following base units:

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: = 1.0 cm × 1.0 cm × 1.0 cm = 1.0 cm^{3}


SI Units
The metricbased Système International or SI units are used to standardize the report or calculation of scientific quantities:

Outside the United States, the word "meter" is spelled "metre" and the word "liter" is spelled "litre." 

Metric Prefixes
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 mostcommonly used in chemistry are listed in red):

In addition to the base metric units, many other scientific quantities also employ this system of prefixes:


The metric prefixes can be employed to scale the base units so that they can represent anything from a very large numeric value (for example by using prefixes such as Exa, Tera, or Mega) to a very small numeric value (for example
by using prefixes such as Atto, Femto, or Pico). Scaling the unit up or down when reporting measurements is good practice because:
In addition to the standard metric prefixes, the Ångstrom is also a commonly used unit that arises in measurements on the atomic scale:



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