TOPICS: CLASS INTRODUCTION HANDLING NUMBERS (SIG FIG’S, SCI NOT) CHEMISTRY 151, GENERAL CHEMISTRY I LECTURE

REQUIRED TEXT, ETC: Chemistry and Chemical Reactivity, Kotz and Treichel, 4 th Edition Student Solutions Manual by Alton Banks Scientific pocket calculator with exponential notation and logarithms (TI 30 or higher) Laminated Periodic Table Saunders Interactive General Chemistry CD-ROM (optional)

COURSE DESCRIPTION: GENERAL CHEMISTRY I: Prerequisites: MAT 122 and CHM 080 or CHM 130 with a grade of C or better, or placement on the chemistry assessment at the CHM 151 level. The course “General Chemistry I” is designed for science majors and pre-professional (pre- med, pre-pharmacy, etc.) students. The lecture covers the fundamentals of matter, stoichiometry, chemical reactions, electronic structure of atoms and molecules, bonding theory, and states of matter.

ARE YOU IN THE RIGHT CLASS??? Don’t wait too long to decide CHM 80 opportunities abound See me if the first several lectures are too fast paced and “you are lost” Majority of material in Chapters 1-3 is considered “review material” from prior chem class(es).

HELP: This is a “high risk” class: many try, not all succeed. Please take advantage of all opportunities to assure that you will emerge successful: Attend every class Do all homework as assigned, as soon as it has been covered in class. Use the Study Guide to check your answers after you complete assignments. Read the book! Work through the in-chapter problems. Study the various charts, tables, models and diagrams.

Get yourself into a study group. Ask me for help as soon as the need arises: schedule an appointment if you can’t drop by at my scheduled hours. Drop by the egroup chat room and leave a question. Call me by voic when emergencies arise. Don’t wait! Take advantage of the tutoring center, West Campus CFA 171

Handling Numbers in Chemistry: The Necessary Skills Correct use of significant figures (“sig figs”) Handling scientific notation Rounding off computational values Knowledge of SI, Metric, and English Units Use of dimensional analysis as problem solving tool

Correct use of significant figures (“SF’s”) All measured values are limited in scope by the accuracy of the instrument used. When correctly expressed, all measured values contain all the digits which can be read directly plus one estimated digit. The digits in measured values are described as “significant figures” when they are presented in this fashion.

TEST YOUR MEMORY, Counting SF’s:

Correct Number of SF’s:

RECALL THE RULES, COUNT ONLY: 1. All non zero digits: 2.35 cm, 3 SF g, 4 SF 2. All Internal zeros: oz, 4 SF 3. All ending zeros when the decimal point is expressed: 2.00 lb, 3 SF 2.0 in, 2 SF 200. ft, 3 SF

DO NOT COUNT AS SIG FIGS: 1. Ending zeros, no decimal point 2000 g, 1 SF 2. All beginning zeros.0005 g, 1 SF

GROUP WORK: How many SF’s?

ANSWERS, GROUP WORK:

SCIENTIFIC NOTATION Scientific Notation is an alternate method of expressing numerical values in which the original value is multiplied or divided by ten until there is only ONE digit to the left of the decimal. The resulting number is multiplied by 10 raised to the appropriate power to restore the worth of the original value.

1,000,000 = 1.00 X 10 6 (3 SF) or 1 X 10 6 (1 SF) = 2.70 X = x10x10x10x10 27,000 = 2.70 X 10 4 = 2.70 x10x10x10x10 Scientific Notation is used to express very large and very small values, and to facilitate expression of some value to correct number of SF’s.

= = = = = 27.0 x 1 = 27.0 x Small Numbers: subtract one from the power of ten for each right move of decimal: = x 10 0 = 2.7 x = 2.7 X Large Numbers: add one to the power of ten for each left move of decimal: 27,000= 27,000 x 10 0 = 2.7 x = 2.7 X 10 4

In a nutshell: Add +1 to power of ten for each LEFT MOVE Add -1 to power of ten for each RIGHT MOVE

GROUP WORK Place into Scientific Notation: 95,000 (4 SF’s) X X X 10 +4

ANSWERS 95,000 (4 SF’s) = X X = 5.93 X = X X = X = X X = X 10 +6

SF’S IN CALCULATIONS When doing calculations involving measured values (always the case in science!), you must limit the number of digits in your results to reflect the degree of uncertainty introduced by these values. You must be familiar with the rules for number of SF’s or digits allowed and also with the rules for rounding values down to the allowed number of digits.

Calculations Involving SF’s Multiplication and Division: The final answer in a computation involving these operations should have no more SF’s than the value in the original problem with the least number of SF’s. Addition and Subtraction: The sum of these operations is allowed no more digits after the decimal than the original value with the least number of digits after the decimal.

Rounding off Answers to Correct # SF’s If first digit to be dropped is <5, drop it and all following digits, leaving rest of number unchanged. Round off to 4 SF’s: = Less than five

If the first digit to be dropped is >5, drop it and all following digits, but increase the last “retained digit” by one: Round off to 4 SF’s: = >5

If the first digit to be dropped is exactly five, no non zero digits following, “even up” the resulting rounded-off value: Increase the last retained digit to make it even if it is odd only. Round off to 4 SF’s: = = Note: = = End, Lecture 1 January 2001

SF’s in Calculations, Samples: 1.30 in. X.20 in. X in. = in. 3 = 7.7 X 10 2 in. 3 3 SF 2 SF 4 SF 2 SF allowed 1.30 in. Since one value has.20 in. no digits after decimal, in. none are allowed! in. = 2962 in.

METRIC AND SI UNITS Prefixes you should know: M, 1,000,000 (10 6 ) X basic unit “mega” k, 1,000 (10 3 ) X basic unit “kilo” d, 1/10 (10 -1 ) X basic unit “deci” c, 1/100 (10 -2 ) X basic unit “centi” m, 1/1000 (10 -3 ) X basic unit “milli” , 1/1,000,000 (10 -6 ) X basic unit “micro” n, 1/1,000,000,000 (10 -9 ) X basic unit “nano” p, 1/1,000,000,000,000 ( ) X basic unit “pico”

Common SI/Metric/ English Conversions (Know!) 1000 g = 1 kg 1000 mg = 1 g (1 g = kg ) (1 mg = g) 1 lb = g 16 oz avoir = 1 lb SI / English gateway 1. MASS

1 m = 100 cm = 10 3 mm 1000 m = 1 km (1 cm = m) (1 m = km) (1 mm = m) 1 m = 10 9 nm = pm 2. LENGTH: cm = 1 inch 1 yd = 3 ft = 12 in yd = 1 mi SI/ ENG gate

3. VOLUME: 1 L = 1000 mL = 1000 cm 3 1 qt =.9463 L= mL SI / ENG GATE 1 qt = 2 pt 1 gal = 4 qt 1pt = 16 fl oz