Prefixes SI unit, 9

With SI units, prefixes are used to indicate decimal liractions or multiples of various units. For example, the prefix milH- represents a 10 fraction, one-thousandth, of a unit A milligram (mg) is 10 gram (g), a millimeter (mm) is 10 meter (m), and so forth. TABLE 1.5 presents the prefixes commonly encountered in chemistry. In using SI units and in working problems throughout this text, you must be comfortable using exponential notation. If you are unfamiliar with exponential notation or want to review it, refer to Appendix A.l. 

Prefixes. In SI, 20 prefixes are used and are direcdy attached to form decimal multiples and submultiples of the units (see the introduction to this volume, p. xvi). Prefixes indicate the order of magnitude, thus eliminating nonsignificant digits and providing an alternative to powers of 10 eg, 45 300 kPa becomes 45.3 MPa and 0.0043 m becomes 4.3 mm. 

X 1023 hydrogen atoms), which is written 1.0000 mol H, is the chemical amount of hydrogen atoms in the sample. Take the advice of your instructor on whether to use the formal term. Like any SI unit, the mole can be used with prefixes. For example, 1 mmol = 10 3 mol and 1 pmol = 10 6 mol. Chemists encounter such small quantities when dealing with rare or expensive natural products and pharmaceuticals. 

The Systeme International d Unites (International System of Units) has the abbreviation SI. It includes base units, supplementary and derived units which together form a coherent system of units. Prefixes are used to form decimal multiples and sub-multiples of the SI units. 

Each of the SI units may have a prefix, the most commmon are ... 

The prefixes should be attached directly to the SI base unit e.g., kilogram, millisecond, gigameter, etc. Similarly, the abbreviations attach directly to the abbreviation for the SI units e.g., cm, Mg, mK, etc. Do not use two or more of the SI units. Although kilogram is the normal base unit for mass, the prefixes are added to gram (g), not kilogram (kg). 

Care the odd-looking units of B require us to cite the gas constant R in SI units with prefixes. 

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. 

The measurement system that you will most likely encounter is the SI (Metric) system. Each quantity (such as mass and volume) has a base unit and a prefix that modifies the base unit. The prefixes are the same for all quantities and are based on a decimal system. Below are some basic SI units we will introduce others in later chapters ... 

As shown above, the SI unit for volume is the cubic meter (m3), but most chemists use the liter (L, which is equal to 1 cubic decimeter (dm3)) or milliliter (mL). Appendix A lists the SI base units and prefixes, as well as some English-SI equivalents. 

One reason for the great diversity of units in existence is the fact that quantities of such diverse magnitudes are measured. A general rule is that the unit should be appropriate in magnitude to the quantity being measured. To obtain a dimension of convenient size in SI units, the SI unit is multiplied by a power of 10 and the prefixes listed in Table B.3 are affixed to the unit. 

TABLE 2. STANDARD prefixes USED WITH SI units ... 

Decimal multiples of the coherent base and derived SI units are formed by attaching to these units the prefixes shown in Table 2. 

---