Science 9

Chemistry

A key role of Chemistry is to tell us all about patterns in the properties and behaviors of matter. Patterns are an important aspect of nature because they allow us to know things about substances. If something is part of a pattern, we can predict certain things about it. Of course, to ensure our knowledge is correct, we can test our predictions, and Science does this all the time. Also, if something is part of a pattern, we know how to classify it. This is important because making predictions about things, testing our predictions and using the results to classify things are ways of learning about the world around us.

You can see patterns in properties everywhere. For example, some things are explosive while others are stable even if you heat or pound them. Certain materials dissolve in water but others are unaffected even if you leave them soaking in it. Glassy materials are hard but plastics are soft and easily scratched.

And, what types of behaviors do we study in chemistry? Just a few are: a startled octopus changing the color of its skin, eggs turning white as they cook, a candle "disappearing" as it burns, a battery getting back its energy as it recharges, a leaf making food for its tree.

The Chemistry section of Science 9 focuses on tiny particles called atoms and how they join together (bond) to form larger particles called molecules. We will learn about the chemical and physical properties of atoms and of molecules and what happens to these particles during the behaviors mentioned above.

The Particle Theory of Matter This theory has five points:

1. all matter is made of extremely tiny particles (much, much smaller than cells!)

2. each pure substance is made of just one kind of particle

3. particles attract each other

4. particles are always in motion

5. the temperature of the particles controls how much they move about.

Classifying Matter Classifying things is a way of learning about them because it helps us to see

similarities and differences. A simple classification system of matter is based on the physical states of matter, i.e., solid (s), liquid (l), and gas(g).

Q. Create a classification chart based on the hair colors of your classmates. Look around and record the different hair colors and the number of students that fit into each hair color category. Then, use the data in your classification chart to create a bar graph. Label the X axis with the colors of hair. Up the Y axis, place the numbers indicating how many students belong in each hair color category. Use a large enough range of values. Which hair color is the most common?

Q. Create a classification chart based on the states of matter. Look around and record the number of objects that fit into each category (each state.) Then, use the data in your classification chart to create a bar graph. Label the X axis with the states of matter. Up the Y axis, place the numbers indicating how many objects belonged in each state. Use a large enough range of values. Which state is the most common?

The following table or chart is a more complicated but more accurate way of classifying matter. This type of chart would be more difficult for you to use, because, at this point, you may not understand all the terms. And, if you were given a sample of something to classify, how would you know where to place it in the chart? An important part of chemistry is performing tests on materials to determine where they belong in the chart. The tests reveal certain properties of the substances and the properties tell us where in the table the materials belong.

Changes We will look at two types of changes - physical and chemical. Physical changes do not change the basic nature of the thing we are investigating. For example, if we are testing the strength of the metal handle of a hockey stick, we can bend it until it breaks but we still have the same material at the end of the investigation. But, a chemical change creates new matter. To test the combustion temperature of a piece of flame retardant material for safety clothing, the material could be put in an oven. At some point, it would start to smoke and then to burn. After the test, we would have a small pile of ash - quite a different material than we started with.

Q. Look at the following processes. In each one, some change is taking place. Describe what the change is. Then, label the changes as "physical" or "chemical." Explain your choice of labels. Remember, the key is if something new is being made.
a) you sharpen your pencil
b) you erase a pencil line
c) you bake a cake
d) you use battery power to play your portable CD player.

Another way of distinguishing chemical and physical changes is the ease of reversing them. Physical changes can be reversed easily but chemical changes can be reversed only with difficulty, sometimes only through a complicated process. A problem here is that students new to the field of Chemistry may not be able to judge what is "easy" and "hard" to do. At this point in your study of Chemistry, a certain change may seem hard to reverse but later, you would realize it is actually easy to reverse. As you gain experience with the subject, this type of decision will become much easier to make.

Q. Which of the following changes do you think could be easily reversed?
a) water to ice
b) building a Lego model
c) exploding a firecracker
d) growing a rose.

Mechanical Mixtures Recall that the classification table above lists two types of mixtures - mechanical mixtures (heterogenous) and solutions (homogenous.) the components of mechanical mixtures are loosely combined - you can see the components. (Sometimes a magnifying glass may be needed.) Ordinary mechanical mixtures are things like beach sand; you can separate a sample into the individual grains just by letting them slowly slide off the side of your hand. A suspension is another example of a mechanical mixture because, again, you can se the components. Think of muddy water. Let the suspension sit for a while and gravity will drag down the heavy particles of dirt, leaving a somewhat clear layer of water at the top. A colloid is a special type of suspension in which the particles are so small gravity alone can not pull them to the bottom of the container. Magnification is especially useful to see the components of this type of mixture. Also, shining light in through the side of the container allows us to see the very small particles because they scatter it just like tiny particles in the atmosphere scatter blue light. Which of these types of mixtures do you think is easier to "pick apart?"

Q. You mix small amounts of the following pairs of ingredients. Devise a way of separating each mixture into its components. Later, we may test your ideas in lab.
a) salt and pepper
b) salt and sand
c) sugar and salt
d) salt and iron filings.

Q. Why are these mixtures called heterogenous?

Solutions This is the other branch of Mixtures from the classification table. A solution consists of two components - the solvent that does the dissolving and the solute that gets dissolved. Often, the solvent makes up more of the solution than the solute. One property of a solution is clarity. Look through a salt water solution -- you "see" nothing. Alloys are solutions made by heating two or more metals, stirring them and letting the solution cool. We could say an alloy is a type of solid solution. Alloys have been important in the history of Technology and Industry. Solutions are more difficult to separate into their components.

Q. Which is the solvent and which is the solute in the following solutions?
a) the atmosphere and CO₂
b) coffee and water
c) chocolate powder and milk
d) blood and O₂ from our lungs
e) water and cola flavoring

Q. Research. Choose two of the following alloys and for each, create an original (no cutting and pasting) 100 word summary including: approximate date of discovery, components, uses. Use the Internet or encyclopedias or reference books on technology or invention.

Choose from among: bronze, steel, Wood's metal, the metal in coins, yellow gold

Pure Substances There are two types of pure substances - elements and compounds. A sample of an element contains just separate atoms (all the same kind) while a sample of a compound contains molecules (clumps of different kinds of atoms.) Think of a handful of Legos. Each color is a type of atom. Grab a handful of red and stick them together and you have a sample of an element because it contains only one kind of Lego, only one kind of atom. Start sticking together red and green pieces and you are making a sample of a compound because it contains two types of Legos, two types of atoms. You must learn what symbols represent atoms and what ones represent compounds. Also, you must learn the names of common elements and of common compounds. A special chart the Periodic Table contains the symbols and names of all the known elements, more than a hundred. We will use this chart often for the rest of the section on Chemistry.

Q. Research. Create an original (no cutting and pasting) 150 summary on the alchemists. These secretive researchers lead the way for the development of chemistry (although chemistry did not develop directly from alchemy.) Use the Internet or encyclopedias or reference books on technology or invention.

Atomic Theory Recall the Legos. If you were asked to make a sample of some element, say oxygen for example, how many colors would you snap together? How many pieces would you snap together? What if you were asked to make a sample of water? How many colors and how many pieces of each color would you use? John Dalton's Atomic Theory helps us answer these questions. Once you know the answers to these types of questions - memory and practice. Note: before Dalton published his ideas, the investigations of four famous researchers, Davy and Faraday (Br.) and Lavoisier and Proust (Fr.), suggested atoms formed molecules by joining together (bonding) in definite ratios. This is how Science works; each new researcher uses the ideas of their predecessors.

Chemical reactions are a type of sentence describing chemical changes during which atoms or molecules are combined to give them a chance to break apart and reform into new materials. The reaction, when it is balanced, shows you how many of each type of atom or molecule is involved in the process. It is one thing to know what types of atoms or molecules might be involved in some type of chemical change; it is another thing, an important thing, to be able to say how many are involved. Balancing equations requires patience, attention and practice.