Christopher G. Hamaker, Illinois State University, Normal IL© 2008, Prentice Hall

Chapter 1Introduction to Chemistry

INTRODUCTORY CHEMISTRYINTRODUCTORY CHEMISTRYConcepts & Connections

Fifth Edition by Charles H. Corwin

Christopher G. Hamaker, Illinois State University, Normal IL© 2008, Prentice Hall

Chapter 1 2

Chemistry, The Central Science

• Knowledge of chemistry is important to understanding the world around us.

Chapter 1 3

Modern Chemistry

• Chemistry is a science that studies the composition of matter and its properties.

• Chemistry is divided into several branches:– Organic chemistry is the study of substances

containing carbon.

– Inorganic chemistry is the study of all other substances that don’t contain carbon.

– Biochemistry is the study of substances derived from plants and animals.

Chapter 1 4

Scientific Investigations

• Science is the methodical exploration of nature followed by a logical explanation of the observations.

• The process of scientific investigation entails:– Casual or conscious observation that lead to formation

of question(s)– planning an investigation– carefully recording observations– gathering data– analyzing the results – Form additional questions or

experiments

Chapter 1 5

The Scientific Method

• The scientific method is a systematic investigation of nature and requires proposing an explanation for the results of an experiment in the form of a general principle.

• The initial, tentative proposal of a scientific principle is called a hypothesis.

Chapter 1 6

Scientific Method, continued• After sufficient evidence, a hypothesis becomes a scientific theory.

A scientific theory provides an explanation to explain the cause of the phenomenon supported by experimental results

• A natural law is a measurable predictable relationship within a set of conditions. Natural law does not attempt to explain the cause of observable phenomenon

Chapter 1 7

Significant Figures

Significant figures - all digits in a number representing data or results that are known with certainty plus one uncertain digit

Chapter 1 8

Recognition of Significant Figures

• All nonzero digits are significant

• 7.314 has four significant digits

• The number of significant digits is independent of the position of the decimal point

• 73.14 also has four significant digits

• Zeros located between nonzero digits are significant

• 60.052 has five significant digits

Chapter 1 9

Use of Zeros in Significant Figures

• Zeros at the end of a number (trailing zeros) are significant if the number contains a decimal point.

• 4.70 has three significant digits

• Trailing zeros are insignificant if the number does not contain a decimal point.

• 100 has one significant digit; 100. has three

• Zeros to the left of the first nonzero integer are not significant.

• 0.0032 has two significant digits

Chapter 1 10

How many significant figures are in the following?

1. 3.400

2. 3004

3. 300.

4. 0.003040

Chapter 1 11

How Many Significant Figures?

Round off each number to 3 significant figures:

1. 61.40

2. 6.171

3. 0.066494

Chapter 1 12

correct answer 152.83 liters

Significant Figures in Calculation of Results

Rules for Addition and Subtraction

• The result in a calculation cannot have greater significance than any of the quantities that produced the result

• Consider:

37.68 liters 6.71862 liters

108.428 liters 152.82662 liters

Chapter 1 13

)calculator(on 109688692.210255.2

)94.15(102.4 84

3

Which number has the fewest significant figures? 4.2 x 103 has only 2

The answer is therefore, 3.0 x 10-8

Rules for Multiplication and Division

• The answer can be no more precise than the least precise number from which the answer is derived

• The least precise number is the one with the fewest significant figures

Chapter 1 14

Scientific Notation

• Used to express very large or very small numbers easily and with the correct number of significant figures

• Represents a number as a power of ten

• Example:

4,300 = 4.3 x 1,000 = 4.3 x 103

Chapter 1 15

• To convert a number less than 1 to scientific notation, the original decimal point is moved x places to the right, and the resulting number is multiplied by 10-x

• The exponent x is a negative number equal to the number of places the decimal point moved

0.0534 = 5.34 x 10-2

Chapter 1 16

Types of Uncertainty

• Error - the difference between the true value and our estimation– Random– Systematic

• Accuracy - the degree of agreement between the true value and the measured value

• Precision - a measure of the agreement of replicate measurements

Chapter 1 17

Critical Thinking: Reactions with Oxygen

• What do burning wood, rusting iron, and exploding gasoline have in common?

• All three are examples of combustion.

• Combustion is a chemical reaction of a substance with oxygen.

• Rusting is slow reaction, burning is rapid reaction, and an explosion is instantaneous reaction.