Metric system prefixes used

Chemists routinely measure quantities that run the gamut from very small (the size of an atom, for example) to extremely large (such as the number of particles in one mole). Nobody, not even chemists, likes dealing with scientific notation (which we cover in Chapter 1) if they don t have to. For these reasons, chemists often use a metric system prefix (a word part that goes in front of the base unit to indicate a numerical value) in lieu of scientific notation. For example, the size of the nucleus of an atom is roughly 1 nanometer across, which is a nicer way of saying 1x10- meters across. The most useful of these prefixes are in Table 2-2. 

You measure a length to be 0.005 m. How can this be better expressed using a metric system prefix ... 

Chapter 2. Chemistry and Measurements, looks at measurement and emphasizes the need to understand numerical relationships of the metric system. Significant numbers are discussed in the determination of final answers. Prefixes from the metric system are used to write equalities and conversion factors for problem-solving strategies. Density is discussed and used as a conversion factor. 

Scientific measurements are expressed in the metric system. As you know, this is a decimal-based system in which all of the units of a particular quantity are related to one another by factors of 10. The more common prefixes used to express these factors are listed in Table 1.2 (page 7). 

One of the main advantages of the metric system is that the same prefixes are used with all quantities, and they always have the same meanings. 

The system of units used in chemistry is the SI system (Systeme International), which is related to the metric system. There are base units for length, mass, etc. and decimal prefixes that modify the base unit. Since most of us do not tend to think in these units, it is important to be able to convert back and forth from the English system to the SI system. These three conversions are useful ones, although knowing the others might allow you to simplify your calculations ... 

The metric system, or Systeme International d Unites (SI system as it is commonly known), is the predominant system of measurement in the world. In fact, the United States is one of only about three countries that do not commonly use the metric system. The metric system attempts to eliminate odd and often difircult-to-remember conversions for measurements (5,280 feet in a mile, for example). It is a decimal-based system with standard terminology for measurements of length, volume, and mass (weight). It also uses standard prefixes to measure multiples of the standard units. 

One major advantage of the metric system is that it uses a decimal system, which means all units are related to smaller or larger units by a factor of 10. Some of the more commonly used prefixes along with their decimal equivalents are shown in Table 1.2. From this table, you can see that 1 kilometer is equal to 1000 meters, where the prefix kilo- indicates 1000. Likewise, 1 millimeter is equal to 0.001 meter, where the prefix milli- indicates Xooo- You need not memorize this table, but you will find it a useful reference when you come across these prefixes in your course of study. 

In 1960 the International General Conference on Weights and Measures adopted an improved form of the metric system, The International System of Units (SI). The units of mass, length, and time are the kilogram (kg), meter (m), and second (s). The following prefixes are used for fractions and multiples ... 

The metric system consists of a base unit and (sometimes) a prefix multiplier. Most scientists and healthcare providers use the metric system, and you are probably familiar with the common base units and prefix multipliers. The base units describe the type of quantity measured length, mass, or time. The SI system is sometimes called the MKS (meter, kilogram, second) system, because these are the standard units of length, mass, and time upon which derived quantities, such as energy, pressure, and force, are based. An older system is called the CGS (centimeter, gram, second) system. The derived CGS units are becoming extinct. Therefore, we will focus on the MKS units. 

The heart of the metric system is its use of prefixes. Many of the prefixes are ones that you already know. Table 15.1 lists all of the ones that you need to know. 

Prefixes are used in both systems, but they are more commonly used in the metric system because the metric system is base-10. 

To use exponential notation to work with very large and very small numbers To use the basic elements of the metric system—a system of units and prefixes designed to make scientific calculations as easy as possible... 

The metric system problem, part (a), can be solved without paper and pencil— by moving the decimal point in 5.200 three places to the right. The English system conversion, part (b), requires that we remember the number of yards per mile (harder than the 1000 m/km metric conversion factor) and that we use pencil and paper or a calculator to do the arithmetic. The conversion factor 1000 is used for kilograms, kilohters, kilowatts, and any other factor involving the prefix kilo-. The English conversion factor 1760 yd/mile is not used in any other conversion. 

The primary unit of length in the metric system is the meter, which is 3.37 in. longer than a yard. The same prefixes are used with the meter as with all other metric units. 

The metric system and its newer counterpart, SI, use subunits and multiples of units that are equal to powers of 10, and they also use the same prefixes to mean certain fractions or multiples, no matter what primary unit is being modified. The meter is the primary unit of length the gram is the primary unit of mass and the liter (the cubic meter in SI) is the primary unit of volume. The prefixes centi-(0.01), (0.001), and kilo (1000) are used with any of... 

The problem of changing over a highly industrialized nation such as the United States to a new system of measurements is a substantial one. Once the metric system is in general use in the United States, its simplicity and convenience will be enjoyed, but the transition period, when both systems are in use, can be difficult. Nevertheless, it will be easier than it seems. While the complete SI is intimidating because it covers every conceivable kind of scientific measurement over an enormous range of magnitudes, there are only a small number of units and prefixes that are used in everyday life. 

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. 

The metric system uses grams to measure weight and liters to measure volume, as shown in Table 7.1. Prefixes are used to indicate the value (Table 7.2). The apothecaries system uses ounces and pounds for weight and teaspoon, and tablespoon to measure volume. Table 7.3 contains conversion factors for the apothecaries system and metric system. 

TABLE 1-5 Common Prefixes Used in the SI and Metric Systems ... 

The prefixes used in the SI and metric systems may be thought of as multipliers. For example, the prefix kilo-indicates multiplication by 1000 or 10, and milli- indicates multiplication by 0.001 or 10. ... 

The metric system is an alternative way to measure distances, volumes, and masses. Once you understand what the prefixes mean and what the basic terms used for measurement are, you will have no problem dealing with these units. For example, meters (m) are used to measure length. 

The prefixes are used to modify the base unit, such as the meter (m), to make larger or smaller units that are more appropriate for a particular use. The most often used units of length in the metric system are shown in the following table. 

For many years scientists recorded measurements in metric units, which are related decimally, that is, by powers of 10. In 1960, however, the General Conference of Weights and Measures, the international authority on units, proposed a revised metric system called the International System of Units (abbreviated SI, from the French 5ysteme /ntemationale d Unites). Table 1.2 shows the seven SI base units. All other units of measurement can be derived from these base units. Like metric units, SI units are modified in decimal fashion by a series of prefixes, as shown in Table 1.3. We will use both metric and SI units in this book. 

The meter can be divided into subunits (Fig. 2-1), and multiples of the meter can be defined. The metric system uses the same prefixes to define the subunits and multiples for the meter as it does for all its other units, which is a great advantage. The most important prefixes for us to learn in the metric system are presented in Table 2-2, along with their meanings. 

The same prefixes are used with mass as with distance, and they have the same meanings. That is one facet that makes the metric system so easy. In the English system, the subdivisions of a yard are a foot—one-third of a yard—and an inch—one-thirty-sixth of a yard. The subdivision of an Avoirdupois pound is an ounce, one-sixteenth of a pound. The subdivision of a Troy pound is an ounce, one-twelfth of that pound. (Gold and silver are measured in Troy ounces.) Each type of measurement has a different subdivision, and none is a multiple of 10. The metric system uses the same prefixes for all types of measurements, they are all multiples of 10, and they always mean the same thing. The symbols for the units and prefixes are easier to learn than those for the English system units. For example, pound is abbreviated lb and ounce is oz, whereas the metric prefixes are almost always closely related to their names. It is easier to convert metric measurements because the prefixes mean some multiple of 10 times the fundamental unit. 

Metric system. The system of units used by scientists in which multiples or subdivisions of units are powers of 10 times the unit, and all such multiples or subdivisions are designated by the same prefix no matter what unit is involved. 

Conversion of units within the metric system may be accomplished by using the factor-label method as well. Unit prefixes that dictate the conversion factor facilitate unit conversion (refer to Table 1.1). 

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