Metric prefixes of SI units

Chemistry is full of calculations. Our basic goal is to help you develop the knowledge and strategies you need to solve these problems. In this chapter, you will review the Metric system and basic problem solving techniques, such as the Unit Conversion Method. Your textbook or instructor may call this problem solving method by a different name, such as the Factor-Label Method and Dimensional Analysis. Check with your instructor or textbook as to for which SI (Metric) prefixes and SI-English relationships will you be responsible. Finally, be familiar with the operation of your calculator. (A scientific calculator will be the best for chemistry purposes.) Be sure that you can correctly enter a number in scientific notation. It would also help if you set your calculator to display in scientific notation. Refer to your calculator s manual for information about your specific brand and model. Chemistry is not a spectator sport, so you will need to Practice, Practice, Practice. 

Mass The SI unit for mass is the kilogram (kg). Scientists can measure mass using units formed by adding metric prefixes to the unit gram (g), such as milligram (mg). To measure mass, you might use a triple-beam balance similar to the one shown in Figure 12. The balance has a pan on one side and a set of beams on the other side. Each beam has a rider that slides on the beam. 

SI units (SI Systeme fnternational d Unites) The modern coherent rationalized internationally adopted metric system of units. It has seven BASE UNITS and two dimensionless units, formerly called supplementary units. DERIVED UNITS are formed by multiplication and/or division of base units. Standard prefixes are used for decimal multiples and submultiples of SI units, along with standard symbols for both units and prefixes. 

The revised metric system is called the International System of Units (abbreviated SI, from the French Systeme Internationale d Unitds). Table 1.2 lists the seven SI base units. All other units of measurement can be derived from these base units. The SI unit for volume, for instance, is derived by cubing the SI base unit for length. The prefixes listed in Table 1.3 are used to denote decimal fractions and multiples of SI units. This enables scientists to tailor the magnitude of a unit to a particular application. For example, the meter (m) is appropriate for describing the dimen.sions of a classroom, but the kilometer (km), 1000 m, is more appropriate for describing the distance between two cities. Units that you will encounter frequently in the study of chemistry include those for mass, temperature, volume, and density. 

Time The SI base unit for time is the second (s). The frequency of microwave radiation given off by a cesium-133 atom is the physical standard used to establish the length of a second. Cesium clocks are more reliable than the clocks and stopwatches that you use to measure time. For ordinary tasks, a second is a short amount of time. Many chemical reactions take place in less than a second. To better describe the range of possible measurements, scientists add prefixes to the base units. This task is made easier because the metric system is a decimal system. The prefixes in Table 2-2 are based on multiples, or factors, of ten. These prefixes can be used with all SI units. In Section 2.2, you will learn to express quantities such as 0.000 000 015 s in scientific notation, which also is based on multiples of ten. 

Recall from Chapter 2 that the universal unit system used hy scientists is called Le Systeme Internationale d Unit6s or SI. It is a metric system based on seven base units—meter, second, kilogram, kelvin, mole, ampere, and candela—from which all other units are derived. The size of a unit in a metric system is indicated by a prefix related to the difference between that unit and the base unit. For example, the base unit for length in the metric system is the meter. One tenth of a meter is a decimeter where the prefix deci- means one tenth. And, one thousand meters is a kilometer. The prefix kilo- means one thousand. 

Another important measurable quantity is mass, which can be defined as the quantity of matter present in an object. The fundamental SI unit of mass is the kilogram. Because the metric system, which existed before the SI system, used the gram as the fundamental unit, the prefixes for the various mass units are based on the gram, as shown in Table 5.5. 

Units give a scale on which to represent the results of a measurement. The three systems discussed are the English, metric, and SI systems. The metric and SI systems use prefixes (Table 2.2) to change the size of the units. 

The SI unit of mass is the kilogram (kg), which is interesting for a few reasons. It is the only basic SI unit defined with a prefix (kilo) already in place, and it is the only one defined by reference to a physical object—a mass of platinum-iridium held at Sevres in France. To express the large quantities of material that we encounter in the extraction and processing of ores it is usual to use the metric ton (sometimes written toime symbol t) ... 

SECTION 1.4 Measurements in chemistry are made using the metric system. Special emphasis is placed on SI units, which are based on the meter, the kilogram, and the second as the basic units of length, mass, and time, respectively. SI units use prefixes to indicate fractions or multiples of base units. The SI temperature scale is the Kelvin scale, although the Celsius scale is frequently used as well. Density is an important property that equals mass divided by volume. 

Decimal fractions and multiples of metric and SI units are designated by using the prefixes listed in Table G.2. The prefix kilo, for example, means a unit is multiplied by 10 ... 

Like all metric systems, SI units have the advantage that prefixes representing various multiples or submultiples may be used to increase or decrease the size of the unit by various powers of 10. Some of the more common prefixes and their symbols are shown in Table 2.2. 

The metric system, or International System (SI, from Systlme International), is a decimal system of units for measurements of mass, length, time, and other physical quantities. Built around a set of standard units, the metric system uses factors of 10 to express larger or smaller numbers of these units. To express quantities that are larger or smaller than the standard units, prefixes are added to the names of the units. These prefixes represent multiples of 10, making the metric system a decimal system of measurements. Table 2.1 shows the names, symbols, and numerical values of the common prefixes. Some examples of the more commonly used prefixes are... 

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