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Problem 1
Fill in the blanks in this concept map to help you tie together the key concepts concerning elements, atoms, and molecules.
- Create a concept map to organize your understanding of the life-supporting properties of water. A sample map is in the answer section, but the value of this exercise is in the thinking and integrating you must do to create your own map.
Problem 2
Problem 3
Changing the _________ would change it into an atom of a different element.
a. Number of electrons surrounding the nucleus of an atom
b. Number of protons in the nucleus of an atom
c. Electrical charge of an atom
d. Number of neutrons in the nucleus of an atom
Problem 4
What is chemically nonsensical about this structure?
Problem 5
A solution at pH 6 contains _________ H+ than the same amount of a solution at pH 8.
a. 20 times more
b. 100 times more
c. 2 times less
d. 100 times less
Problem 6
Most of the unique properties of water result from the fact that water molecules
a. Are the most abundant molecules on Earth's surface.
b. Are held together by covalent bonds.
c. Are constantly in motion.
d. Are polar and form hydrogen bonds.
Problem 7
A can of cola consists mostly of sugar dissolved in water, with some carbon dioxide gas that makes it fizzy and makes the pH less than 7. In chemical terms, you could say that cola is an aqueous solution where water is the _________, sugar is a _________, and carbon dioxide makes the solution _________.
a. solvent . . . solute . . . basic
b. solute . . . solvent . . . basic
c. solvent . . . solute . . . acidic
d. solute . . . solvent . . . acidic
Problem 8
The atomic number of sulfur (S) is 16. Sulfur combines with hydrogen by covalent bonding to form a compound, hydrogen sulfide. Based on the number of valence electrons in a sulfur atom, predict the molecular formula of the compound. (Explain your answer.)
a. HS
b. H₂S
c. H₄S₂
d. H₄S
- In what way does the need for iodine or iron in your diet differ from your need for calcium or phosphorus?
Problem 9
Problem 10
Use carbon-12, the most common isotope of carbon, to define these terms: atomic number, mass number, valence. Which of these numbers is most related to the chemical behavior of an atom? Explain.
Problem 11
In terms of electron sharing between atoms, compare nonpolar covalent bonds, polar covalent bonds, and ions.
Problem 12
The diagram below shows the arrangement of electrons around the nucleus of a fluorine and a potassium atom. What kind of bond do you think would form between these two atoms?
- Look back at the abbreviated periodic table of the elements in Figure 2.5B. If two elements are in the same row, what do they have in common? If two elements are in the same column, what do they have in common? Would you predict that elements in the same row or the same column will have similar chemical properties? Explain.
Problem 13
- What do you think the effect on the properties of water would be if oxygen and hydrogen had equal electronegativity?
Problem 14
Problem 15
A recent experimental study looked at the combined effects of ocean acidification and increased ocean temperatures, both aspects of climate change, on the growth of polyps, juvenile coral animals. Researchers reported the average polyp biomass (in μg/polyp) after 42 days of growth under four treatments: a control with pH and temperature maintained close to normal reef conditions, a pH lowered by 0.2 units, a temperature raised by 1°C, and a combined lower pH and higher temperature. The results showed that polyp biomass was reduced somewhat in both the low-pH and high-temperature treatments, but the combined treatment resulted in a reduction in growth by almost a third—a statistically significant result. Experiments often look at the effects of changing one variable at a time while keeping all other variables constant.
Explain why this experiment considered two variables—both a higher temperature and a lower pH—at the same time.
- In agricultural areas, farmers pay close attention to the weather forecast. Right before a predicted overnight freeze, farmers spray water on crops to protect the plants. Use the properties of water to explain how this method works. Be sure to mention why hydrogen bonds are responsible for this phenomenon.
Problem 16
Problem 17
This chapter explains how the emergent properties of water contribute to the suitability of the environment for life. Until fairly recently, scientists assumed that other physical requirements for life included a moderate range of temperature, pH, and atmospheric pressure. That view has changed with the discovery of organisms known as extremophiles, which have been found flourishing in hot, acidic sulfur springs and around hydrothermal vents deep in the ocean.
What does the existence of life in such environments say about the possibility of life on other planets?