Category Archives: Chemistry Lesson

Lesson 11: The Electromagnetic Spectrum

Seems like quite a jump from quantifying chemical reactions to learning about the electromagnetic spectrum, but it will soon become clear that in order to understand chemical reactions, we really need to understand electrons and to understand electrons, we need to learn about the electromagnetic spectrum.

Textbook reading:  Chapter 9, Sections 9.1 – 9.4. The Electromagnetic Spectrum and the Bohr Model of the Atom, pp. 285-294.

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Supplemental

Before we jump into the electromagnetic spectrum, let’s spend a minute learning about waves. You may have read that light and its relatives in the spectrum travel in waves. What does that mean?

Think about physical waves, like the waves in the ocean. Electromagnetic waves exhibit a similar motion. Check this interactive website from Colorado to see how you can create varying waves with different motions.

Of course, Bozeman Science also has an introduction to waves with cool animations to help you understand what you did at the interactive site.

EM_Spectrum3-new

(Illustration from NASA)

Although electromagnetic radiation forms a continuous ribbon of wavelengths, we cut the ribbon into segments and name different regions based on their size and related properties. Electromagnetic radiation has been mined over the years to produce many useful gadgets, which helps us relate to the different types.

Moving from left to right, we find that the first piece of the ribbon, radio waves, are the largest (the illustration suggests as big as buildings). Besides sending sound to radios, radio waves are are used in astronomy. For example, radar and radio waves were used to investigate the recent asteroid that passed by the Earth. Currently the largest telescope to detect radio waves from space is the Arecibo Radio Telescope in Puerto Rico.

Microwaves consist of wavelengths shorter than radio waves. They are used for all sorts of things besides cooking, including remote sensing of weather for forecasting, as well as for monitoring space. Some forms are also used for communications.

Nearer to the visible spectrum (forms of electromagnetic radiation we can see), are the infrared waves. We can’t see infrared radiation with our eyes, but we can sometimes feel it is as heat. Certain snakes, called pit vipers, have organs on their heads that can detect infrared radiation as a way to find their prey in the dark. Humans rely on equipment, such as specially designed cameras, to observe infrared radiation. Your TV remote works using infrared waves.

We are most familiar with the wavelengths in the visible spectrum. Once again, the wavelengths are continuous, not discrete regions. Sir Isaac Newton paved the way by breaking white light into its components with a prism and naming bands of wavelengths as colors. Although realistically they could be broken into any number of colors, he gave us seven: red, orange, yellow, green, blue, indigo and violet.

Ultraviolet radiation has a slightly shorter wavelength than visible light. Humans can’t see ultraviolet light, but many other animals can, including honey bees and butterflies. In fact, many flowers have spots we can not see in visible light, but that show under ultraviolet light. Scientists call these spots and patterns “nectar guides” because they are thought to attract bees and other pollinators to the flower.

X-rays are a form of electromagnetic radiation with a very short wavelength. X-rays are considered to be “ionizing radiation,” which means its energy levels are high enough that when it strikes a molecule it can remove an electron, thus forming an ion. Because of this property, exposure to X-rays should be limited.

Certain gamma rays have the highest level of energy of all the forms of electromagnetic radiation, as well as the shortest wavelength. Here on earth gamma rays are only produced by lightning, radioactive decay of certain radioactive elements, and nuclear explosions. In space they are produced by high-energy events such as supernovas. Gamma rays are mostly harmful, but they can also be helpful because they are used to treat certain cancers and to kill bacteria in food.

Particles

The various forms of electromagnetic radiation were long known to behave like waves, but also they also act like particles. Scientists call these elementary particles photons. They are odd particles because they have no mass or charge, and could be thought of as bundles of energy or “quanta.” At motion in a vacuum, photons travel at a constant rate: the speed of light c = 2.998 x 108 m/s. One way photons behave like particles is when they collide with electrons.

Bohr Model of the Atom

Where is all this going? Niels Bohr used data from light emission spectra of elements to develop his famous model of the atom.

Emission_spectrum-H

Visible lines in the hydrogen emission spectrum (public domain image from Wikimedia)

Bohr’s observations that atoms of different elements emit light at only certain wavelengths lead him to conclude that electrons are fixed positions from the nucleus. Check out the ladder analogy in Figure 9.10 on page 293 in your text.

340px-Bohr_Model.svg

(Public domain image from Wikimedia)

Although Bohr’s model has been widely adopted in popular culture, it only had the power to explain the hydrogen emission spectrum, not those for elements. Obviously, something more was needed. We will learn about how the model has be modified over the years in our next lesson.

Lesson 10: Quantities in Chemical Reactions

Pull out those calculators as we delve back into math problems.

Textbook Reading:  Chapter 8, pp. 249 to 271.

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Supplemental:

After reading through this chapter, I realized using ratios is a good way to do these calculations, but when they get long and complicated there is always the chance of missing units or accidentally flipping one of the conversion factors.

55 g Na x 2 moles Na/ 33 g Na x 56.7 g Na/1 mole NaCl….. It goes on and on.

One way to add structure to these calculations is to use proportions. To help you get started, I put together a video explaining the method. Even if you don’t choose to use the ratios and proportions, you may find some of the information about determining molar mass and moles helpful.

You can also use this method for finding percentages and even for the heat of reaction calculations.

Bozeman Science explains some of the concepts from the chapter as well (he uses the strings of ratios like the textbook):

Remember, the answers to the odd-numbered problems at the end of the chapter are given in the back of the book. You might want to try a few to make sure you understand them.

If you choose, let me know if you have any questions.

Lesson 9: Classifying Chemical Reactions

Now for the second half of chapter 7:

Textbook Reading:  For lesson 9, please read Chapter 7, pp. 218 to Key Terms on top of page 238.

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Supplemental:

A. One way to classify chemical reactions is by what type of chemistry is happening.

1. Precipitation reactions 

These are some of the more memorable reactions in chemistry, particularly because there is a clear sign that a reaction has occurred. Whether or not a precipitate forms has to do with solubility of the products.

Did you understand what spectator ions are?

2Na+(aq) + 2Cl(aq) + Cu2+(aq) + SO42−(aq) →

2Na+(aq) + SO42−(aq) + CuCl2 (s)

Can you find the spectator ions in the equation above? If not, try this tutorial. Can you find the precipitate in this reaction? (Answer posted here)

One of your classmates suggested this beautiful precipitation reaction between potassium iodide and lead (II) nitrate. Enjoy!

2. Acid-Base or Neutralization Reactions

When acids and bases are added together, the end products are often water and a salt (ionic compound).

lemon

3. Gas Evolution Reactions

Remember the baking soda and vinegar volcanoes you did as child? Those frothy bubbles were caused by the release of carbon dioxide gas, making it an example of a gas evolution reaction.

4. Oxidation-Reduction or “Redox” Reactions

Although mentioned here, we don’t have all the chemistry knowledge we need to completely understand these reactions. We’ll visit them again in Chapter 16 after we learn more about electrons and bonding.

Combustion is a specific type of oxidation-reduction reaction.

Note: The reaction of octane to form carbon dioxide and water in an internal combustion engine is shown on the bottom of page 227.

2C8H18 + 25O2 ==> 16CO2 + 18H2O

This is the idealized reaction under the best possible conditions. In reality the combustion of gasoline produces CO (carbon monoxide), NO (Nitrogen Oxide), O3 (ozone), etc. These side reactions can result in serious air pollution issues.

B. A second way to classify reactions is to look at what the atoms are doing.

1. Synthesis or combination
2. Decomposition
3. Displacement (or called single replacement)
4. Double-displacement – double-replacement

People have come up with a number of fun ways to remember these reactions, for example:

Classifying Chemical Reactions (with reference to the) Flintstones


Or you might remember this poster involving happy/sad faces.

Hope you found that helpful. Please let me know if you have any questions!

Lesson 8: Chemical Reactions Part 1

Because there is so much information packed in this unit, we’re going to split chapter 7 and work on it over 2 weeks.

Textbook Reading:  For lesson 8, please read Chapter 7, pp. 205- 217 (Sections 7.1-7.5).

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Supplemental:

As we learned from the oscillating reaction in Lab 6, chemical reactions are more complicated than simply reactants forming products. In this TED Video called If molecules were people…. you will see chemical reactions from an interesting new perspective.

((Psst: let me know if you like this video, because TED has a number of high energy, fun videos about chemistry like this.))

How do you know if there even has been a chemical reaction? Unfortunately you don’t see arms moving to the face like in the video. But you can look for the evidence:

  • Color change
  • Formation of a solid
  • Formation of a gas
  • Heat absorption
  • Heat emission
  • Light emission

Once we establish there has been a chemical reaction, now we also need to make sure the chemical equations we use are balanced. Section 7.4 has specific information about how to go about balancing an equation.

If you are still not clear on balancing equations after reading the text, or if you would like to see it presented in a different way, you might want to try this A Beginner’s Guide to Balancing Equations video from Bozeman Science.

Did you find the colored molecules helpful?

Solutions and solubility are briefly introduced in this chapter, but will be covered more completely in Chapter 13. Because we are going to be doing some experiments with solutions in lab, let’s go through some basic vocabulary.

The solute is the smallest part of a solution, or the substance being dissolved.

The solvent is the larger part, or the part doing the dissolving.

A solution is a solute dissolved in a solvent.

Miscible means two substances that can mix, and particularly that they can form solutions in any proportion. That means that both substances can be present as the smaller portion or as the larger portion.

By the way, immiscible simply means two substances that can’t mix.

What is the difference between saturated, unsaturated, and supersaturated? Here’s a quick video that really explains clearly:

Recrystallization involves making a supersaturated solution and then adding more solute. This causes the solute to fall out of solution in the form of pure crystals.

Finally, what is the effect of temperature on solutions?

You probably have direct experience trying to add sugar to a cold drink versus a hot drink. Isn’t it easier to stir in sugar and have it dissolve quicker when the liquid is warmer? Solids in general are more soluble at high temperatures and less soluble at low temperature.

SolubilityVsTemperature(image pubic domain)

As you can see from the graph, however, not all salts follow this general trend. Each salt will have its own solubility curve of how much of the substance will dissolve into the solvent at a given temperature.

Hope you found that helpful. Please let me know if you have any questions!

Lesson 7: Calculating Chemical Composition

We are taking a side trip back into the realm of math as we learn how to figure out the numbers of atoms and molecules in certain masses of substances, calculate mass percent composition, and delve into empirical and molecular formulas. Get out those calculators!

Textbook Reading:  Chapter 6, pp. 165-194 (Yes, that includes the examples in the Chapter in Review.)

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Supplementary

The measurement techniques in this chapter have many practical applications. For example, chemists and chemical engineers are interested in how much starting material is needed to produce a specific amount of end product most efficiently. As pointed out in the first part of the chapter, health care workers often use these measurements to help ensure patients receive proper care and nutrition. Knowing how to perform these calculations can even help you save money at the gas pump.

food label

Matter can be measured in several ways. You might count how many of something you have, or you might determine the mass or volume. 

The mole, also called Avogadro’s number, is a very large number (6.022 x 1023) that allows us to convert between mass and number of molecules. Moles are used extensively in chemistry and it is very important to understand how they work.

Molar mass is the mass of one mole of any chemical compound, typically with units of g/mol. The lightest possible chemical is hydrogen gas, but there is no limit to how heavy a chemical compound can be. Macromolecules (large organic compounds such as DNA) can weigh thousands of grams per mole.

Mr. Isaacs at IsaacsTeach has 3 short videos that really help to explain moles and how to use them. Pull out your calculator and periodic table (one that lists atomic mass) to work along with the videos.

1. The Mole Concept

2. Molar Mass

3. Molar Volume

 
Mr. Causey has a video about How to Calculate Percent Composition, Empirical Formulas, etc.



 

So, you made it through the chapter. How did it go? Be sure to let me know if you have any questions or comments.

Lesson 6: Molecules and Compounds

For this week’s lesson we are going to find out how to name chemical compounds.

Textbook Reading:  Chapter 5, pp. 127 – 153
Take a look at Problems 105 on page 160 and 107 on page 162

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Supplemental:

After reading the chapter, I’m sure you have some questions about naming molecules. Think of it as learning a new language, with rules of grammar and new vocabulary to learn. We’ll be going over examples in lab, but in the meanwhile here is some additional information that should help.

First, it would be really handy to have a copy of what is called a “Periodic Table of Ions.” This link to ScienceGeek has a free .pdf to download and print out if you don’t already have one.

Take a look at the Periodic Table of Ions and you will begin to see some patterns. The first group (first column of the periodic table) is called the alkali metals. They always give up an electron and become positive ions with a single +. The next group, the alkali earth metals, always give up two electrons, so they become ions with 2+. The next group (column 3), give up three electrons and are 3+.

The transition metals through the middle of the table don’t follow patterns as nicely and some have multiple states. That’s why we need a table to help us!

Over on the far right of the table, the wacky noble gases in column 18 do not give up electrons, which means they don’t form ions. They also are very stable and don’t form compounds with other elements. Next to the noble gases, the nonmetals tend to gain electrons and form negative ions. Group 17 is the first group to the left of the noble gases and is called the halides. They gain one electron and have  1- charged ions. At the top of column 17 notice that hydrogen has sneaked into this group as well, sometimes gaining an electron to become the hydride ion. In group 16 to the left, the atoms gain 2 electrons for 2- charged ions. Finally, the group 15 nonmetals gain 3 electrons for -3 charged ions. The rest do not form a clear pattern, and once again, you will need to refer to the table.

Hint:  Go back over the table and shade the groups with strong patterns with different colored pencils or highlighters.

Methane-3D-balls(Public domain image)

Are you ready to name this molecule with one carbon and four hydrogen atoms yet? It is commonly called methane, but that name doesn’t give you any information about its structure. How would you name it using the rules for naming molecules?

Mr. Anderson at Bozeman Science has two helpful videos about naming compounds. He goes over the same material as the text, but in a different way, which might help your understanding.

Naming Compounds – Part 1 (direct link)

Did you notice the name for the molecule above, CH4, at about 4:50 in the video? Did you find benzoate in your table of polyatomic ions on the Periodic Table of Ions printout?

Naming Compounds Part 2 (direct link)

Here’s a list of Greek words used in naming:
1= mono (isn’t used much
because the 1 is understood)
2 = di
3 = tri
4 = tetra
5 = penta
6 = hexa
7 = hepta
8 = octa
9 = nona
10 = deca

Want to reinforce your knowledge of the common polyatomic ions from Table 5.6 on page 141 in the text? Quizlet has flashcards and self-quizzes (with pronunciations).

As usual, please leave a comment or e-mail if you have any questions.

Edit:

Another way to remember those polyatomics (direct link)

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Optional:

This animation allows you to build models of some common molecules. To start, select a molecule in the box towards the middle.

Lesson 5: Atoms and Elements

This week’s lesson is jam-packed with important information. Please take time to go over it carefully, and write down any questions you might have.

Textbook Reading:  Chapter 4, pp. 91-114

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Supplemental:

public-domain-Atom_(PSF)

Atoms are pretty amazing to think about, and our knowledge of them is increasing all the time.

I have a friend who used to ask me, “Has anyone ever seen an atom?” Recently scientists have developed technology that allows us to do just that. It is called an atomic force microscope/scanning tunneling microscope.

This video from Nature shows us what atoms look like through one of these microscopes, as well as introducing some of the reasons why looking at atoms is useful (direct link).

How small are those atoms we just looked at? This TED video helps put it all into scale (direct link)

Finally, in this video Mr. Causey explains atoms, isotopes and ions and then helps you figure out how many protons, neutrons and electrons are found in some common examples (direct link).

Some other useful resources:

Theodore Gray has gone a long way towards making the elements more easy to relate to with his periodic table of element photographs at http://periodictable.com. To look at each element, click on the photograph. His periodic table is also available as a book and as cards.

You might also want to check out this interactive period table.

Should you memorize the elements? I don’t think it is necessary to memorize every one, but you would benefit from learning the abbreviations for the most common elements, especially when we start doing reactions. Free Rice has a quiz/game to help you learn the basic symbols and once you’ve them, the full list of symbols. What level can you get to?

Optional video:
Are you interested in history? Bozeman Science gives an overview of how various parts of the atom were discovered and how the model of the atom changed. (direct link)

Since you are getting a break with lab this week, be sure to spend some extra time on this very important chapter. Feel free to contact me if you have any questions.

Lesson 4: Energy

What is energy? Why is it included in a chapter about matter? How are the two related?

Textbook Reading:  Chapter 3, part 2, pp. 66- 83

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Supplemental:

I. Energy

We use the word energy every day. We hear phrases like “energy crisis,” “running out of energy,” or “high energy bills.” Unfortunately, what we commonly mean by “energy” in these cases is some kind of fuel or other consumable resource.

In science, energy does not mean fuel. Instead, it is a more abstract concept:  “the capacity to do work.” It is not really anything concrete. It is not an object, but instead is a property that objects have.

Here’s what the famous physicist, Richard Feynman, had to say about energy:

There is a fact, or if you wish a law, governing all natural phenomena that are known to date. There is no exception to this law – it is exact so far as is known. The law is called the conservation of energy It says that there is a certain quantity, which we call energy, that does not change in the manifold changes which nature undergoes. That is a most abstract idea, because it is a mathematical principle; it says that there is a numerical quantity, which does not change when something happens. It is not a description of a mechanism, or anything concrete; it is just a strange fact that we can calculate some number and when we finish watching nature go through her tricks and calculate the number again, it is the same.

(Feynman, R. (1963).The Feynman Lectures on Physics. Book 1. New York: Addison-Wesley.)

What he is saying is that energy is a mathematical principle and no more. Isn’t that something to get your mind around?

A useful way to think about it is to think of various situations as “energy stores” rather than energy itself. These are situations with potential capacity to do work.

Some examples of energy stores:
1. Chemical (for example, alcohol + oxygen)

fireChemical energy stores can be used to move automobiles (internal combustion) and hot air balloons.

2. Kinetic (found in a moving object)

running-movement

3. Gravitational (due to the position of an object in a gravitational field)

gravitational
If you are sitting in a tree and drop a large rock, the gravitational energy will be transformed to kinetic energy. If your aim is good, you could drive in a stake with the dropped rock.

4. Elastic (for example, in a stretched rubber band or compressed spring)

rubber-band

5. Thermal (in a warm object)

coffee-heat-smallerThermal energy is important in determining the states of matter, as shown in this video (direct link).  Be sure to watch this one because the animations will help you visual the changes that occur between different states.

 

6. Magnetic (in magnets that are attracting or repelling )

johnny_automatic_magnet(Clipart from OpenClipArt)

Think of all the work a magnet can do.

7. Electrostatic (in two separated electric charges that are attracting, or repelling)

1024px-Lightning_over_Oradea_Romania_zoom

8.  Nuclear (released through radioactive decay, fission or fusion)

radiation
II. Introduction to Endothermic and Exothermic Reactions

As we study chemical reactions later in the course, we will find out that sometimes they release energy and sometimes they absorb energy. Our textbook is giving only a brief introduction in this chapter.

This video also gives an overview of endothermic and exothermic reactions (direct link).


III. Temperature versus Heat

Heat and temperature are further examples of vocabulary words with precise meanings in science that aren’t used as precisely in other contexts.

Temperature: A measure of a substance’s thermal energy (using a thermometer).

Heat: Thermal energy transfer or exchange between substances or objects.

temperature-versus-heat

Make sure you understand how to convert temperature units back and forth from Kelvin, Celsius and Fahrenheit, pp 71-73.

IV. Heat Capacity

We will be investigating heat capacity in lab this week, so pay particular attention to the terms heat capacity, specific heat capacity and the formula on page 75.

Maybe we’ll learn something that will help keep us cool.

Lesson 3: Matter

Now we move to the “nucleus” of chemistry:  matter!

Textbook Reading: Chapter 3, page 55 to top of page 66. We’ll save the Energy part of the chapter for next week.

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Supplemental information:

As we learned in the first lesson, matter is anything that takes up space and has mass. In this chapter, Tro discusses some different ways to classify matter.

1. States of Matter

Even though matter can be found all over the Universe, you only find it in a few forms, called the “states” or sometimes “phases.” The textbook introduces you to three states of matter:  solid, liquid and gas (page 57). Did you know that there are other states of matter as well? Now people generally recognize at least five states of matter!

Plasma

Plasma is widely considered to be the fourth state of matter. What is it? Plasma is a gas in which the atoms are ionized, meaning there are free negatively-charged electrons and positively-charged ions.

This video explains plasma (if the viewer doesn’t work, here’s a direct link).

Hopefully we’ll get to explore more about plasma in the future.

Bose-Einstein Condensates

If plasma is super high energy, then Bose-Einstein condensates are the exact opposites. Satyendra Bose and Albert Einstein predicted that matter would change state at temperatures approaching absolute zero way back in the 1920s, but no one was able to verify the existence of these condensates until 1995.

Here, one of the scientists who made a Bose-Einstein condensate explains what they are like (direct link):

Interested in learning more? The Chem4Kids website covers the basics of the five main states of matter in a particularly clear way.

 

2. Classifying Matter According to Composition

Matter can also be grouped according to what makes it up. If it is a pure substance, it contains only one kind of atom (an element), or molecule with different kinds of atoms (called a compound). In this case, the ratio of atoms in the compound is always the same.

Mixtures contain varying amounts of atoms in a combination of substances. If the mixture is uniform, it is called homogeneous. If you can point to something in the mix and say that substance is different from the rest, then it is called heterogeneous.

Pay particular attention to Figure 3.8 on page 59. We will be going over some concrete examples in class.

3. Chemical and Physical Properties

We will be investigating the physical properties of matter in our laboratory this week. Some physical properties are boiling point, density, and color. We’ll be learning a lot more about chemical properties as we progress through the book.

This video goes over the differences between chemical and physical changes in more detail if you’d like some clarification.

(Direct link if viewer is not working)

4. Law of Conservation of Mass

When French chemist Antione Lavoisier figured out that phylogiston was not part of combustion, he also realized that nothing was being created nor destroyed during chemical reactions. We might not always immediately realize where each substance is going in a reaction, but eventually we can track it down.

Pay particular attention to that tiny sidebar on page 65. We now know the law of conservation of mass is an oversimplification. It works with most chemical reactions, but in some nuclear reactions changes in mass do occur.

That’s it. Not so bad was it?

If you have any questions whatsoever, please leave a comment, send an e-mail or comment to the Yahoo group.

Lesson 2: Measurement and Problem Solving

For this lesson we’re going to learn about scientific notation, significant figures, and units of measurement. If you have taken other science courses in the past, you are likely to find at least some of this section to be a review. For those of you who have never experienced these techniques and concepts, this is undoubtedly the most tedious section in the book. Give it your best effort, however, because once you’ve learned it, you will be able to apply it to many fields.

Textbook Reading:  Chapter 2 Measurement and Problem Solving (pp. 11-44)

Helpful practice:
Please do Skillbuilder 2.4 at the top of page 17 (answers on page 53).
Be sure to read and understand Examples 2.18 – 2.25 on pages 40-42. If you struggled with the density calculations in the last lab, look at examples 2.27 and 2.28 on pages 43-44.
Also, do Problem 42 on page 46 (answers for even numbered problems are in the back).

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Still unsure about scientific notation after reading the text? Math is Fun has a scientific notation tutorial where you can type in your own examples to test (optional).

This video goes over significant figures (like in the textbook), and then gives a cool shortcut to use at the end.

(If the video player doesn’t work, link to YouTube)

Finally, this video gives a laid back review of measurement and units. You can zone out when he mentions accuracy, precision and percent error, as those are not covered in the Tro text.

(Direct link)

Please let me know if you have any questions. We will be going over examples at our meeting.

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A Chemistry Sidebar:

mL vs ml

Have you seen milliliter abbreviated mL or ml and wondered which is correct?

According to the U.S. Metric Association (USMA):

“The symbol for liter (or litre) may be either a capital el (L) or a lowercase el (l); both are correct. In the U.S., Canada, and Australia, the capital el (L) is preferred, but most other nations use the lowercase el (l).”

So there you have it!