Chapter 1: The Scientific Method Chemistry = The science that seeks to understand what matter does by studying what atoms and molecules do.

Observation = A way of acquiring information about nature. Simple descriptions (qualitative observation) Number (quantitative observation) Hypothesis = A tentative explanation of your observations Falsifiable: a test may invalidate your hypothesis Experiments = Tests of hypotheses, laws or theories Results either Validate (confirm) or Invalidate (deny) your ideas Law = A statement that combines all past observations Predict future observations You cannot choose to violate a scientific law Theory = An explanation that extends beyond individual observations to an understanding of the underlying causes for the way nature is or behaves Models of nature This is what the scientific method is made of

Observation: anything wrong with this picture?

Observations Hypothesis Law Theory Experiments This is how the scientific method works

The (meaningful) beauty of the scientific method Source:

Measurement = Quantitative observation Comparison to an agreed upon standard Every measurement has a number and a unit Scientists have measured the average global temperature rise over the past century to be 0.6 °C The number tells you 1.what multiple of the standard the object measures 2.the uncertainty in the measurement The number tells you 1.what multiple of the standard the object measures 2.the uncertainty in the measurement The unit tells you what standard you are comparing your object to The unit tells you what standard you are comparing your object to Chapter 2: Measurements and Problem Solving

Scientific Notation is a way of writing large and small numbers The sun’s diameter is 1,392,000,000 m An atom’s average diameter is m The sun’s diameter is x 10 9 m An atom’s average diameter is 3 x m Large Number = Positive Exponent x 10 9 m Large Number = Positive Exponent x 10 9 m Small Number = Negative Exponent 3 x m Small Number = Negative Exponent 3 x m

Writing a number in scientific notation 1,392,000,000 m 1.Locate the decimal point 2.Move the decimal point until a number between 1 and 10 is obtained 3.Multiply the new number by 10 n 4.n is the number of places you moved the decimal point 5.Large number? n is positive Small number? n is negative 1,392,000,000. m 1.392,000,000. m x 10 ? 9 m x 10 9 m

Significant Figures Writing Numbers to Reflect Precision Exact Values Can be obtained by counting or by definition Exact values have “unlimited significant figures” Measurements Are obtained from instruments The number of significant figures reflects the instrument precision. All the digits written are known with certainty except the last one, which is an estimate 1.2 grams Certain Estimated

Counting Significant Figures m 1.Non-zero digits are significant 2.Zeroes in between non-zero digits are significant 3.Zeroes on the right of the last non-zero digit are significant 4.Zeroes on the left of the first non-zero digit are not significant Important exception 1: Exact numbers. Numbers that come from 1.Counting 2.Formulas Are not measurements and have an infinite amount of sig. fig. Important exception 2: Ambiguous numbers. A number has an ambiguous amount of sig. fig. if: 1.It is bigger or equal to 10 2.It has no decimals 3.It ends with a zero 10 Fingers > 100 Miles

How many significant figures are in each of the following numbers? × items (In a dozen) 100,000 Counting Significant Figures. Examples.

Multiplication and Division with Significant Figures When multiplying or dividing measurements with significant figures, the result has the same number of significant figures as the measurement with the fewest number of significant figures 5.02 × 89,665 × 0.10= = 45 3 sig. figs. 5 sig. figs. 2 sig. figs. 2 sig. figs ÷6.10= = sig. figs. 3 sig. figs. 3 sig. figs.

Addition and Subtraction with Significant Figures When adding or subtracting measurements with significant figures, the result has the same number of decimal places as the measurement with the fewest number of decimal places = = dec. pl. 3 dec. pl. 3 dec. pl. 2 dec. pl = = dec. pl 3 dec. pl. 1 dec. pl.

The Standard Units Scientists have agreed on a set of international standard units for comparing all our measurements called the SI units Système International = International System QuantityUnitSymbol lengthmeterm masskilogramkg timeseconds temperaturekelvinK