Name: Date: Class: Lesson 7: Scientific Notation, SI Units, and Unit Conversions

Transcription

1 NOTES Name: Date: Class: Lesson 7: Scientific Notation, SI Units, and Unit Conversions Scientific Notation Scientists often use numbers that are very large (number of atoms in 1 ml of water or 2.7 grams of salt) or very small (diameter of a ribosome or length of a bacterial cell). These numbers are usually bulky to write, so we have a method of writing them in a more compact way using powers of 10. Scientific notation: writing a number as the product of a number between 1 and 10 multiplied by 10 raised to some power STEPS: 1. Move the decimal point in the original number so that it is located after the first nonzero digit. 2. Multiply this new number by 10 raised to the proper exponent (power). The proper exponent is equal to the number of places that the decimal point was moved. 3. The sign on the exponent indicates the direction the decimal was moved. Decimal moved right negative exponent Decimal moved left positive exponent Check your work: A negative exponent indicates the number is smaller than 1. A positive exponent indicates the number is greater than 1. 1

2 Example #1. Write 5284 in scientific notation. Example #2. Write 4,500,000,000 in scientific notation. Example #3. Write in scientific notation. Practice. Write the following numbers in scientific notation ,700, Practice. Write the following numbers in standard notation

3 International System of Units (SI Units) The commonly used SI base units are a choice of seven well-defined units which by convention are regarded as dimensionally independent. This system is currently used by most of the countries in the world in scientific, technical, commerce, and industry work. SI BASE UNITS: MEASUREMENT UNIT UNIT ABBREVIATION LENGTH TIME TEMPERATURE MASS AMOUNT OF SUBSTANCE Which SI unit would be used to measure? 1. The mass of a gold bar 2. The temperature of a gas storage tank 3. The length of a garden hose 4. Number of atoms in 2kg of Lithium 5. The time required to run 800 m Derived Units All other measurements are derived from (a combination of) the seven SI units derived through multiplication or division. They have special names: area = volume = density = speed = 3

4 PRACTICE: Indicate whether the following are measurements of length, area, volume, mass, density, time or temperature. a. 5 ns b. 3.2 kg/l c µm d. 540 m 2 e. 173 K f. 15 ml g. 2 cm 3 h. 4.5 g/cm 3 i g Metric System: you should memorize how to convert to and from the base unit 4

5 Unit Conversions: While the units most commonly used in Chemistry are grams (g) and centimeters (cm), we also must know how to perform dimensional analysis to convert from one unit to another using conversion factors. Three important parts about the unit multiplier: it must cancel (or eliminate) the old unit it must introduce the new unit we are not changing the value of the measurement since the unit multiplier is equal to 1 Examples/Practice: Show all work with unit multipliers (with units). Circle final answer. ONE STEP UNIT MULTIPLIERS hm = m CAREFULLY COPY EXAMPLE FORMAT 2. 4,198 cg = g kl = L g = dag L = ml ,000 µl = L 5

6 TWO STEP UNIT MULTIPLIERS hm = dm CAREFULLY COPY EXAMPLE FORMAT 8. 9,100,000 mg = kg dam = cm dg = dag ,100 cl = hl kg = cg 6