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

Chemistry, The Central Science Knowledge of chemistry is important to understanding the world around us. Chapter 1

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

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

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

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

Significant Figures Significant figures - all digits in a number representing data or results that are known with certainty plus one uncertain digit Chapter 1

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

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

Determining Significant Figures How many significant figures are in the following? 3.400 3004 300. 0.003040 Chapter 1

How Many Significant Figures? Round off each number to 3 significant figures: 61.40 6.171 0.066494 Chapter 1

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 correct answer 152.83 liters Chapter 1

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 Which number has the fewest significant figures? 4.2 x 103 has only 2 The answer is therefore, 3.0 x 10-8 Chapter 1

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

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

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

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. Chapter 1