1. Is an aluminum rowboat and its contents more or less dense than water while you are sitting in the rowboat on top of the water? Write a conditional argument to justify your answer.

2. Does the following argument establish the truthfulness of the conclusion? Explain.

• P1 If an object floats on top of a liquid, then the object is less dense than the liquid.
• P2 A container full of soda floats on top of water.
• C Soda is less dense than water.

3. The density of an object was experimentally determined five times. The results were 4.37, 4.18, 4.25, 4.47, 4.16 g/mL. What would you report as the density of the object?

4. A metal ball has a mass of 3.2 g and displaces a volume of 2.0 mL. What is the density of the metal ball? (b) Another ball has a mass of 4.8 g and a density of 1.2 g/mL. What is the volume of this ball? (c) A third ball has a density of 2.5 g/mL and a volume of 3.0 mL. What is the mass of this third ball?

5. What are the differences between scientific facts and scientific theories?

6. How do you define a good model?

1. Does the following argument establish the truthfulness of the conclusion? Explain.

• P1 If electrons orbit around the nucleus like planets around the sun, then characteristic colors of light are emitted from atoms as electrons fall back to lower energy states after being excited.
• P2 Electrons orbit around the nucleus like planets around the sun.
• C  Characteristic colors of light are emitted from atoms as electrons fall back to lower energy states after being excited.

2. The first atomic particle to be discovered was the electron. With this discovery the first atomic model was created. Describe the first atomic model and tell why it was discarded.

3. Which elements would you predict to be the most similar: (a) Na and Rb or (b) Mg and S? Write a conditional argument to support your choice.

4. Richard Feynman stated he could describe how nature works, but he could not explain why Nature behaves in this peculiar way. Give an example of this from our discussion of atomic theory.

5. Identify each of the following as resulting in either a chemical or a physical change. Justify each answer. (a) Paper is completely burned, (b) salt is dissolved in water, (c) sodium (Na) is placed in water, (d) an orange is peeled.

6. Visit our class homepage. View "Gold Foil Experiment" and "Energy Levels" found under "Assignments" and "Homework Set #2". Read the first page of the Energy Level module, but specifically look at the "Multimedia" section. Write a paragraph that explains why viewing these web pages was or wasn’t useful.

7. In class we viewed the colors emitted by different elements when an electrical potential was applied. Only certain colors were observed and we called this a line spectrum. Why are only certain colors observed?

8. Explain how the red color in fireworks could be produced.

9. What does the current model of the atom allow you to say about the position of an electron in an atom?

1. How are charges produced?

2. What are the three premises that we use when trying to explain charge interactions?

3. Write a sound conditional argument with the following conclusion: The ring floats above the rod.

4. Explain, at the molecular level, what happens to the leaves of an electroscope when a negative rod is placed near (but doesn’t touch) the top of an electroscope.

5. Explain what happens at the molecular level when a positive rod is placed near (but doesn’t touch) a pith ball.

6. When a balloon gets really “charged up” it is observed that any small hairs that happen to be on the balloon stand on end, getting as far away from each other as possible. Explain this observation.

7. Explain, at the molecular level, what happens to the leaves of an electroscope when a negative rod touches the top of an electroscope.

1. Given that HCl turns a solution of water and Neutral Red (an acid-base indicator) the color red and that NaOH turns a solution of water and Neutral Red the color amber. What can you say about NaHCO₃, which turns a solution of water and Neutral Red the color amber? Is NaHCO₃ an acid or a base? Defend your choice.

2. In class we saw that the light bulb did not go on when the wires were placed in tap water. Explain.

3. Describe, at the molecular level, how table salt, NaCl, is formed. Does table salt have molecules? Why do the atoms in table salt stay together?

4. Fill in the following table:

5. Many people believe that the number of electrons in an atom will identify an element, but Ar, K⁺, and Cl^- all have the same number of electrons. Explain.

6. What would the formulas be for the compounds that are formed between: (a) K and O, (b) Sr and I, (c) Li and Br? Give formulas for seven other ionic compounds (salts).

7. View "Making Compounds" under "Content Help" on our class webpage. There are four sections there. Look at each section's "Text" and "Multimedia" (that is four Text and four Multimedia). Write a short evaluation of each.

8. Fill in the column labeled “Acid/Base/Neutral” for each substance in the table below:

1. Two materials have the same molecular mass, but one evaporates faster than the other. Explain.

2. Describe an explain what happens when a charged rod is placed near a small stream of (a) water and (b) Wesson oil.

3. Solid Crisco shortening and liquid Wesson Oil are both fats used for cooking. Why is Crisco a solid and Wesson Oil a liquid at room temperature?

4. Compare a polar molecule with a nonpolar molecule. Draw a model of each.

5. Two materials have the same polarity, but one evaporates faster than the other. Explain.

6. The water molecule has one oxygen and two hydrogen atoms. Why do these atoms stay together?

7. Why does water and oil separate after vigorous shaking?

8. Identify each of the following as ionic, polar, or nonpolar: (a) HCl, (b) N₂, (c) SiO, (d) BaO, (e) LiBr.

9. View "More Detail" under "Making Molecules" under "Content Help" on our class webpage. There are five sections there. Look at each section's "Text" and "Multimedia" (that is five Text and five Multimedia). Write a short evaluation of each.

1. What is the volume of an object that has a mass of 8 g and a density of 2 g/mL?

2. Does the following argument lead to the truthfulness of the conclusion? Explain.

• P1 If an apple floats in water then the apple is more dense than water.
• P2 An apple does float in water.
• C The apple is more dense than water.

3. Does the following argument lead to the truthfulness of the conclusion? Explain.

• P1 If an acid is placed in water then the H⁺ concentration will increase.
• P2 The H⁺ concentration increased.
• C  An acid is placed in water.

4. What is in the air after water evaporates? Is this a physical or a chemical change. Explain.

5. Does the following argument lead to the truthfulness of the conclusion? Explain.

• P1 If electrons reside in discrete energy states, then a line spectrum will be produced after the electrons have been excited.
• P2 Electrons reside in discrete energy states.
• C A line spectrum will be produced after the electrons have been excited.

6. A friend says that water is a good conductor of electricity. What would you tell them?

7. A solution was found to have an H⁺ concentration of 10^-5. (a) Is this solution acidic or basic? (b) What is the pH of the solution? (c) What would be produced if an acid was added to this solution? (d) What would be produced if a base was added to this solution?

8. An atom has 18 electrons and a –1 charge. (a) What element is it? (b) What is the symbol for the ion of this element? (c) Give the formulas for three salts that could be formed using this element.

9. (a) How are ionic bonds formed? (b) Write the formulas for four compounds that have ionic bonds.

10. The density of an object was experimentally determined five times. The results were 1.8, 2.1, 1.99, 2.26, and 2.2 g/mL. What would you report as the density of the object?

11. Why has the solar system model of the atom been discarded?

12. When a person holds on to a device that generates a charge, it is observed that their hair “stands on end,” each hair getting as far away from other hairs as possible. Explain this observation.

13. Using the Gold Foil Experiment, write a sound conditional argument in the If-Then format that has the conclusion: The raisin pudding model must be discarded.

14. (a) How are covalent bonds formed? (b) What is the difference between polar and nonpolar covalent bonds?

15. In the paper chromatography experiment we saw that black ink is made from a combination of different colors. (a) Why did some of the ink spots move in water, but not in alcohol? (b) Explain why a separation of colors was observed by some of the inks in water.

16. Explain what happens to the leaves of an electroscope and why it happens when a rod with a positive charge is placed next to the ball of the electroscope but doesn’t touch it.

17. Consider the experiment with the balloon and Rice Krispies done in class. Write a conditional argument with the following conclusion: The Rice Krispie is attracted to the balloon.

18. Explain what will happen at the molecular level when a rod with a positive charge is placed near a small stream of water that is falling from the tap.

19. (a) What are intermolecular forces? (b) Which has stronger intermolecular forces: polar molecules or nonpolar molecules? Explain.

20. Explain why the boiling point goes up or down in each of the following cases. (a) H₂O (100 ^oC) to H₂S (-60.7 ^oC), (b) H₂S (-60.7 ^oC) to H₂Se (-40 ^oC), (c) H₂Se (-40 ^oC) to H₂Te (-2 ^oC.

21. Determine which liquid, A or B, will evaporate faster in each of the situations given below. If it can’t be determined put “not conclusive.”

22. What is the purpose of a college education? How can this course help to accomplish this purpose? Explain.

1. (a) Predict the graph for an experiment that determines density by changing mass at a constant volume. (b) Predict the graph for an experiment that determines density by changing volume given a constant mass.

2. If a 2.5 kg ball is dropped from rest at a height of 2.0 m, how much kinetic energy does the ball have when at a height of (a) 1.5 m, (b) 1.0 m, (c) 0.5 m, (d) 0.0 m? Assume no heat or other energy is produced.

3. What is the velocity of the ball at each height in problem two?

4. If 5 J of heat is produced during every 0.5 m that the ball travels, what will the kinetic energy of the ball be at each of the heights given in problem two?

5. How much heat is generated if a 3.0 kg ball dropped from rest falls 4.0 m and has 100 J of kinetic energy after falling that 4 m?

6. Explain how a rocket can change directions in outer space.

7. If a person stands on a platform that is able to rotate without friction, points a cordless drill toward the sky, and then turns it on, what will happen. Explain.