Chapter 2: The Atoms and Molecules of Ancient Earth

1.	The number of varies in an element’s isotope. [Hint]
2.	The number of within an atom never varies among atoms of a specific element. [Hint]
3.	The most ancient fossils found are approximately ______ years old. [Hint]
4.	An organic molecule always contains one or more atoms of . [Hint]
5.	Which group of atoms determines a molecule’s behavior? [Hint]
6.	Ninety-six percent of matter found in living organisms is composed of these four elements. [Hint]
7.	A large boulder is balanced on top of a hill. You give the boulder a push, and it rolls down the hill. This is an example of transferring ______ energy into ______ energy. [Hint]
8.	In the chemical equation for burning methane, CH4 + O2 --> CO2 + H2O, CH4 and O2 are the ______ and CO2 and H2O are the ______. [Hint]
9.	Which factor(s) determine(s) whether or not a chemical reaction will occur spontaneously? [Hint]
10.	Which phase of matter has the highest entropy? [Hint]
11.	In a reduction–oxidation reaction, a substance that loses electrons is . [Hint]
12.	Which statement regarding the properties of water is NOT correct? [Hint]
13.	Substances that give up protons (H+) during acid–base reactions are . [Hint]
14.	Which of the following substances is a base? [Hint]
15.	In bonds, electrons are shared between two atoms. [Hint]
16.	A cation has a charge. [Hint]
17.	The bonds between the oxygen and hydrogen atoms within a water molecule are ______ bonds. [Hint]
18.	Which of the following reactants are thought by scientists to have combined to produce formaldehyde and cyanide, the first reduced-carbon products? [Hint]
19.	Why do high temperatures speed chemical reactions? [Hint] To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
20.	Following formation of reduced-carbon compounds, the addition of heat allows ______ bonds to form. [Hint]
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