Reading Notes for Chapter 1

These are Dr. Bodwin's reading notes for Chapter 1 of "Introduction to Chemistry". I am using a local .pdf copy that was downloaded in August 2020.

Chapter Summary:

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Chemistry & Science - What Are We Studying?

Science is a field of study, but it's also a way of thinking. It's based upon curiosity. The core of the scientific method is making an observation and asking a question. After you ask a question, you perform an experiment to test your original observation... this is just another observation. Which leads to another question. And another test. And another observation. Science is always questioning and evolving. This is the scientific method as shown in Figure 1.2 of your textbook, although I would argue that "Make an observation" should be added above the "Propose a hypothesis" box. From the Figure 1.2... saying that birds "can't stand the cold" doesn't really have any context unless you have first made the observation that birds fly south during the winter in the northern hemisphere.

From your textbook science is "the process by which we learn about the natural universe by observing, testing, and then generating models that explain our observations." The term "science" is used in a little broader sense than that, but in the context of your textbook, the important word in that definition is "natural". There are many social science disciplines that often use a scientific approach to their studies, but because they do not study the natural universe, they are not sciences as defined by your textbook. That's why "economics", for example, is not a science in the practice problem in your textbook. {Personally, I have a little bit broader view of the word science, but we'll stick with your textbook's definition for this class.}

Chemistry is the study of matter and its changes. One of my chemistry professors said the plainest definition of chemistry is "stuff changes into other stuff". We'll be looking at properties of different types of matter and how those propertes change as that matter is transformed into other things.

Classification of Matter:

There will be a number of things I call "sorting exercises" in this class. These are useful for categorizing different things into groups that make them easier to understand, but just be cautious because whenever we sort things, there will be some exceptions. At this point, don't focus too hard on the exceptions.

Elements vs Compounds - Something that is made up of a single type of atom are elements; something that is made of two or more types of atoms are compounds.
Elements are the smallest piece of distinct matter; they cannot be further broken down without changing the atomic identity of the substance.
Compounds can be broken down into smaller bits without changing the atomic identity of the atoms that make it up.

Never trust atoms, they make up everything. ;)

Macroscopic Properties vs Microscopic Properties - we will be bouncing back and forth between the microscale (atoms and molecules) and the macroscale (what you hold in your hand) a lot in chemistry, so try to think about that as you look at various properties and changes in matter.

Heterogeneous Mixtures vs Homogeneous Mixtures - This can be pretty obvious in some cases, but rather subtle in others. Any time two or more pure substances are combined, it's a mixture. Heterogeneous means that the mixture is different when it's observed at different points. Macroscopically, chicken noodle soup is a heterogeneous mixture: when you look at one point in the bowl of soup, you find chicken; when you look somewhere else, you find a noodle. Sugar dissolved in water is a homogeneous mixture; everwhere you look, you find sugar water.
Homogeneous mixtures are called solutions.
What about something like tomato juice? Is it a homogeneous mixture or a heterogeneous mixture? A couple good things to look for are:
If it's cloudy, it's almost always a heterogeneous mixture.
If it settle out when you leave it sit undisturbed, it's a heterogeneous mixture.
{That also means that if it can be separated by using a centrifuge it is a heterogeneous mixture. Like blood!}

Phases - Solid, liquid, and gas can be defined in a variety of macroscopic and microscopic ways. At this point, we can use very macroscopic definitions for them that rely upon characterizing the shape and volume of a substance as either "definite" or "variable".

Figure 1.5 gives a nice little flowchart for classifying matter.

Changes in Matter:

Physcial changes only affect the physical form or state of a substance. They are not "chemical reactions". When water freezes, it's still water. When an ice cube is crushed into little pieces, it's still water.
Chemical changes involved breaking and/or forming of chemical bonds and transfer of electrons. When methane burns, it becomes carbon dioxide and water; it's not still methane.

Here Comes the MATH!!!!!

But please don't panic. Math is the language of science, and it just takes some practice. This class is not a "hardcore" math class, but we will have to do some algebra to really understand some concepts. Take a deep breath, calm your mind, and let's ease into the math...

Writing Numbers:

OK, this seems pretty basic, but we need to go over a few things so we can effectively communicate numerical information.

Numbers (almost always) have units. If you don't include the unit, you're not effectively communicating. Units are important because there are often multiple ways that something can be described.
How much gas did I put in my car? 10.
10 what? 10 gallons? 10 dollars? 10 liters? Without a unit, it's not clear.
Today's temperature is 28. Is it a cold winter day or a warm summer day? We don't know without units. In many cases, a unit can be implied, but it is always better to explicitly include a unit. If we're watching a weather report in the United States, 28 probably means degrees Fahrenheitand it's a rather brisk wintery day; if we're in London, England, 28 probably means degrees Celsius and it's a bit warm. Always include units.

Scientific notation: We will at times be dealing with very large or very small numbers. These can be difficult to write in a clearly understandable way.
273510000000000000000 - How many zeros are there? QUICK!! That's kind of hard to count, they all swim together.
0.000000000000654 - How many zeros are there? QUICK!! That's also kind of hard to count.
Scientific notation counts the zeros for you by taking them away from the numerical information.
273510000000000000000 - There are 16 zeros. So we could write this as "27351 x 10¹⁶", but that's still a little awkward. Correct scientific notation moves the decimal until the number can be expressed as a number (between 1 and 10) and a power of 10. So in proper scientific notation, this is 2.7351x10²⁰.
0.000000000000654 - For small numbers, use a negative power of 10. This is 6.54x10^-13.
Calculators and Computers - Scientific notation is enterred a couple different ways in calculator and computer programs. Once fairly common way is using "E" to replace the "x10" part, so the two numbers above would be "2.7351E20" and "6.54E-13". Always check your calculator or computer program so you are using scientific notation correctly.

Significant Figures (Sig Figs): This is a very important concept because it is the way that we communicate the reliability of a number that we are reporting. How many tennis balls fit in the back of a pickup truck? A lot, but how exact does our answer have to be? Doing some quick math, I came up with 3500. Will I be surprised if 3528 tennis balls actually fit? Or if 3462 tennis balls actually fit? Nope, I'm pretty satisfied that 3500 is a good enough answer. "3500" has 2 significant figures. Anything beyond that has some uncertainty. And that's OK. Now, if we were actually putting tennis balls in a pickup truck, we could count them and get an exact number, but how about grains of sand in a soda can? Or bowling balls in the Grand Canyon? There is some uncertainty in those measurements and sig figs tell us where the uncertainty is. They also tell us about the uncertainty in the things we use to measure substances. If you are giving a patient a medication and are told to administer 1.18231638257mL to them, it would ben kind of foolish to try and measure that amount... it needs to be rounded off to an appropriate number of digits. That's what sig figs are - the appropriate number of digits when rounding.

SI/Metric System:

We will most often use SI units, but remember that as long as you are reporting the unit you use, you are clearly communicating.
SI/Metric prefixes - You should know the prefixes in Table 1.3 and be able to convert between prefixes. Many of you are probably used to this when looking at the big prefixes because of computer memory; kilobytes, megabytes, gigabytes, terabytes. The small prefixes are extremely common in medical and healthcare applications.

Converting between values with units (Dimensional Analysis):

We're back to talking about numbers and units again! How many centimeters are in 28.375 inches? How many pounds are in 73.92kg?

"Conversion Factor" - Sometimes I really dislike this term because it sounds like magic. It's not magic. A "conversion factor" is just a way to express the same quantity in two different units. By definition, 1 inch is exactly 2.54 centimeters. That's a conversion factor. 4 inches is exactly 10.16cm. That's also a conversion factor.

28.375 inches to centimeters... I know I have to use 2.54, but do I multiply or divide? Use the units to guide how you set up the problem, just like shown in your textbook.

NOTE: I am well aware that Google will do just about any unit conversion you want it to do, but it's still important to know how to do these without an electronic crutch. Practice unit conversions. Practice writing them out. It's a good way to polish up your skills in a way that's easy to check. Unit conversions are set up the exact same way we will be setting up most math problems, so starting out with good form now will help you out in future chapters.

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