CHAPTER 1 The Chemical World Problems 1 18 21 22 science the study of nature to explain what one observes Consider the following On the first day of school you get in your car and turn the key on the ignition but nothing happens What could be the problem 1 4 THE SCIENTIFIC METHOD How Chemists Think Applying the Scientific Method 1 Propose a hypothesis to explain what is observed 2 Test the validity of the hypothesis by carrying out experiments controlled observations designed specifically to verify or disprove a hypothesis Record observations and analyze the data on the system being studied It s important to keep good records so others can reproduce the work 3 Conduct additional experiments to test the hypothesis under various conditions If all or part of the hypothesis does not hold up to testing then it is adjusted or a new hypothesis is proposed to explain the observations If hypothesis holds up to extensive testing it can lead to the development of a scientific or natural law and or a scientific theory scientific or natural law a simple statement or equation that summarizes past observations and predicts future ones scientific theory a tested broader and deeper explanation of observed natural phenomena Thus a scientific law summarizes what happens a scientific theory explains why it happens Example Many news reports and articles claim that global warming is just a theory How does this demonstrate the lack of understanding by the media and general public regarding scientific theories CHEM 121 Tro Chapter 1 page 1 of 3 1 2 Chemicals Compose Ordinary Things Ex 1 What is your major and why are you taking this class Why do you think knowledge in chemistry is needed in so many different fields Ex 2 What comes to mind first when you hear the word chemical Is it positive or negative Ex 3 Are there chemicals in a cup of coffee Give some examples Thus chemicals are not necessarily hazardous In fact almost everything consists of chemicals since any substance consisting of more than one type of atom is a chemical For example the glass of soda above contains water H2O molecules and carbon dioxide CO2 molecules the lead in a pencil is actually graphite which consists of carbon atoms and we are made of DNA and various other biological molecules or chemicals CHEM 121 Tro Chapter 1 page 2 of 3 1 3 All Things Are Made of Atoms and Molecules Consider molecules of water and carbon dioxide These molecules consist of atoms and their structure at the atomic or molecular level determines their properties and behavior at the macroscopic level i e what we can observe with the naked eye The Structure and Properties of Ice Ice floats on water because ice is less dense than liquid water The strong attraction and repulsion between two different water molecules in ice results in holes or empty space in the ice crystal When ice melts the water molecules fill in the holes so liquid water is more dense than ice Note in ice s molecular level structure the holes have a hexagonal six sided shape Snowflakes have hexagonal symmetry because of the hexagonal holes formed by the arrangement of H2O molecules in ice chemistry the science that studies how matter behaves by understanding the properties and behavior of atoms and molecules that make up the matter CHEM 121 Tro Chapter 1 page 3 of 3