1. CHAPTER 1 - MEASUREMENT Working With Measurements pp. 18 - 22

2. VOCABULARY 1. Significant digits – meaningful digits in a measured quantity 2. Accuracy – how close a measurement is to an accepted or true value 3. Precision – describes how close together or reproducible repeated measurements are.

3. VOCABULARY 4. Resolution – refers to the smallest interval that can be measured 5. Significant difference – two measurements are only significantly different if their difference is much larger than the estimated error.

4. PRECISION VS. ACCURACY Dart Game: Hitting the bulls eye is an example of accuracy. People may demonstrate precision by throwing a group of darts close together, even though they may not be close to the bulls eye.

5. Two Types of Numbers Exact Numbers – Values are known exactly that have defined values or are integers obtained by counting. Example: 2.54cm/inch, 12 inches/foot, 6 moles of iron atoms Inexact Numbers – Values that have some uncertainty Numbers obtained by measurement

6. When measuring, the last digit is uncertain. All digits including the uncertain one are called significant figures (or significant digits) The number of significant figures indicates the exactness of a measurement. Exact numbers theoretically have infinite significant digits!!!

7. Rules for Counting Significant Digits (a.k.a. SigFigs) 1. Non-zero integers always count as significant. 32.7 cm 3 sigfigs 3.7 g 2 sigfigs 1421 km 4 sigfigs 2. Zeros A. Captive zeros are ALWAYS significant 307cm 3 sigfigs 1.007mg 4 sigfigs

8. Rules for Counting SigFigs (cont.) B. Leading zeros are NEVER significant 0.0025 mol 2 sigfigs 0.0264 g3 sigfigs C. Trailing zeros at the right end of a number ARE significant only if there is a decimal point. 100cm 1 sigfig 100.cm 3 sigfigs 100.0cm 4 sigfigs 1200cm 2 sigfigs 2.56 x 10 7 cm 3 sigfigs

9. Rounding Rules If a digit is to be removed… 1.) Less than 5; preceding digit remains same. 2.) Equal to or greater than 5; preceding digit is increased by 1. 1.36  1.4 6.28  6.3

10. BOX AND DOT METHOD 1. Draw a box around all nonzero digits, beginning with the leftmost nonzero digit and ending with the rightmost nonzero digit in the number. 2. If a dot is present, draw a box around any trailing zeros. 3. Consider any and all boxed digits significant.

11. SIGNIFICANT FIGURES Read Significant Figures WS and then Complete SigFigs WS

12. RESOLUTION

13. Find out the resolution of your digital camera (if you own one). What does “megapixel” mean?