I NTRODUCTION TO CHEMISTRY : S CIENTIFIC METHOD, MEASUREMENT, BASIC PROPERTIES OF MATTER M S. B UROKER

Why Chemistry? The Scientific Method The Metric System Measurement: Importance of Numbers LESSON TOPICS Precision and Accuracy

W HAT IS C HEMISTRY ? A basic definition of chemistry would be, _________ _______________________________________________. Matter- _______________________________________.

MAIN BRANCHES OF CHEMISTRY Organic Chemistry  Inorganic Chemistry  Physical Chemistry  Analytical Chemistry  Biochemistry  Theoretical Chemistry 

SCIENTIFIC METHOD The scientific method is not a rigid set of rules, but a general guide for investigation or logical approach to finding answers to questions. 1. Curiosity or a quest for knowledge 2. Design and do experiments, collect data and information, establish facts, and make observations 3. Organize and find relationship between information or data. Formulate a law, a statement of the relationships between facts, data, and observations.

SCIENTIFIC METHOD CONTINUED … 4. Draw conclusions from the observation, data, and facts. Formulate a hypothesis, a tentative explanation of a scientific law. 5. Design new experiments based on the hypothesis, and collect more data, establish more facts, and make more observations. 6. Update laws and hypothesis, ask new questions, and recycle to step 5.

S CIENTIFIC R ESEARCH Pure Research- _________________________ _____________________________________. Applied Research- ______________________ _____________________________________. **** NOTE **** Science and Technology are ____ the same thing! Where science includes knowledge in whatever discipline you’re in; technology is the application of that knowledge for practical purposes. Just a Quick Note … Qualitative Data & Quantitative Data

M EASUREMENTS Science involves making observations and measurements. These measurements involve two things: a number and a unit g

U NITS OF M EASUREMENT We have an international system of measurement … the __________. This is a system of measurement that the world has agreed upon. We need to be aware however; that there is actually one more system called the __________; which stands for centimeter, gram, second.

SI B ASE U NITS Some Basic Properties cgs (subset of the metric system) SI Systemother Length or distance centimetermeterIn, yds, mi Timeseconds hours, days Mass gramskilograms lb, oz Kinetic EnergyErgJoule

D ERIVED U NITS Derived units are _________________ of base units such as mass and volume. Volume … ________________________________. Density … ________________________________.

U NIT C ONSISTENCY Express all units in the same unit of the system … Kinetic Energy= ½ M V 2

UNIT CONVERSIONS It is important, especially for unit consistency, that you are able to move back and forth between units of measurement. Conversion Factors are NOT scary … they are simply ratios that come from two things of different units which are equal to one another in magnitude!! The chemistry is knowing where things go … the solving is just algebra!

D IMENSIONAL A NALYSIS The technique we use that allows us to convert from one unit of measurement to another, is ____________ ____________. ____________________ – a ratio of equal values used to go from one unit to another Example: Can be written as We Use This

R ULES FOR D IMENSIONAL A NALYSIS _____________ 1. ALWAYS start with the _____________ !!! _____________ 2. Draw a _____________ sign and a line 3. Place the unit to be canceled on the bottom _____________ 4. Place a _____________ on the line you have drawn 5. Cross out units and see what you have left. 6. Do the math! #A x #B #A / /

L ET ’ S TRY AN EXAMPLE … Let’ s convert 32.5 inches to feet. How many seconds are in minutes? Convert 65 miles per hour to kilometers per second. (0.625 miles = 1 Km) Conversions with prefixes are done in exactly the same manner, you just have to know the prefixes!!

P REFIXES KiloHectoDecaBasedecicentimilli /101/1001/1000 micronanopico 1/ (1 x ) 1/ (1 x ) 1/ (1 x ) These larger units are multiplications of the base. For example a kilometer is 1000 meters. These smaller units are fractions of the base. For example a centimeter is a 100 th of a meter.

N UMBERS There are two types of numbers in the world 1.) Exact Example: Sample size or n 2.) Nonexact: measurments

M EASUREMENT AND S IGNIFICANT F IGURES All measurements have some uncertainty: 1. the accuracy and precision of the measuring device 2. the skill of the operator 3. the uncertainty principle

ACCURACY VS. PRECISION Accuracy: How closely the measured value is to the true value Precision: How closely the measured values are to one another

MEASURE OF ACCURACY % Error = I correct value – measured value I correct value X 100

Uncertainty There is uncertainty in every measurement we take. We are limited not only by the instruments we use, but also by our own physical limitations. Scientists have devised a way to communicate our “limitations” in a way that we can all have an idea to how much uncertainty there is in a number simply by looking at it!

S IGNIFICANT F IGURES Scientist use significant figures to determine how precise a measurement is. Significant digits in a measurement include all of the known digits plus one estimated digit.

F OR EXAMPLE … Look at the ruler below What would be the measurement in the correct number of sig figs?

L ET ’ S TRY THIS ONE Look at the ruler below What would be the measurement in the correct number of sig figs?

T HE SAME RULES APPLY WITH ALL INSTRUMENTS Read to the last digit that you know Estimate the final digit

L ET ’ S TRY GRADUATED CYLINDERS Look at the graduated cylinder below What would be the measurement in the correct number of sig figs?

O NE MORE GRADUATED CYLINDER Look at the cylinder below… What would be the measurement in the correct number of sig figs?

R ULES FOR S IGNIFICANT FIGURES R ULE #1 All non zero digits are ALWAYS significant How many significant digits are in the following numbers?

R ULE #2 Zeros are ONLY significant if they meet the following criteria: 1.) they are between non-zero digits 2.) they are at the end of a number AND to the right of the decimal How many significant digits are in the following numbers?

R ULES C ONTINUED … All zeros that act as place holders are NOT significant – these are zeros in front of the number or zeros at the end of a number with no decimal. Numbers with zeros at the end and no decimal can be made significant by adding a decimal … or 30.

F OR EXAMPLE 1) ) 6.02 x ) ) ) 800 1) _____________ 2) _____________ 3) _____________ 4) _____________ 5) _____________ How many significant digits are in the following numbers?

R ULE #5 All counting numbers and constants have an infinite number of significant digits … in other words, you do not have to worry about them when performing calculations. For example: 1 hour = 60 minutes 12 inches = 1 foot 24 hours = 1 day There are 30 students in the class

H OW MANY SIGNIFICANT DIGITS ARE IN THE FOLLOWING NUMBERS ? 1) ) ) ) 7.90 x ) ) ) ) _____________ 2) _____________ 3) _____________ 4) _____________ 5) _____________ 6) _____________ 7) _____________

RULES FOR THE COMBINATION OF SIGNIFICANT DIGITS 1. Addition and Subtraction  Round to the least decimal place Add: =  Multiplication and Division  Round to the least significant digit (2.34 x 3.2)/ 5.22=  1.4

W HAT HAPPENS WHEN TO HAVE THE APPROPRIATE AMOUNT OF SIGNIFICANT FIGURES, YOU NEED TO ROUND ??? (want 3 SF) 18.22(want 2 SF) (want 3 SF) (want 1 SF) 98.59(want 2 SF)

1) ) ) ) ) Place the following numbers in scientific notation with 3 SFs: W HAT HAPPENS WHEN TO HAVE THE APPROPRIATE AMOUNT OF SIGNIFICANT FIGURES, YOU NEED TO USE S CIENTIFIC NOTATION ???