![]() that refer to multiples or fractions of a fundamental unit to make a unit more conveniently sized for a specific quantity. SI also defines a series of numerical prefixes A prefix used with a unit that refers to a multiple or fraction of a fundamental unit to make a more conveniently sized unit for a specific quantity. For example, the width of a human hair is very small, and it doesn’t make much sense to express it in meters. Sometimes, a given unit is not an appropriate size to easily express a quantity. A time of 15,000 s can be expressed as 1.5 × 10 4 s in scientific notation. If you have a length that is 2.4 m, then you express that length as simply 2.4 m. To express a quantity, you need to combine a number with a unit. The SI standard unit of length, the meter, is a little longer than a yard. ![]() The SI unit of mass is the kilogram (kg), which is about 2.2 pounds (lb). It is a little longer than a yard (see Figure 2.3 "The Meter"). ![]() Initially, we will deal with three fundamental units. We will use most of the fundamental units in chemistry. (The letters SI stand for the French “le Système International d’unités.”) SI specifies certain units for various types of quantities, based on seven fundamental units One of the seven basic units of SI used in science. Six what? Six miles? Six inches? Six city blocks? The actual distance to the lake depends on what units you use.Ĭhemistry, like most sciences, uses the International System of Units, or SI for short. For example, if you were to ask a friend how close you are to Lake Erie and your friend says “six,” then your friend isn’t giving you complete information. Make new units by combining numerical prefixes with units.Ī number indicates “how much,” but the unit indicates “of what.” The “of what” is important when communicating a quantity.Express units using their abbreviations.Learn the units that go with various quantities.
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