Figure 313 attractions between water molecules o

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Figure 3.13 Attractions Between Water Molecules O BJECTIVE 22 O BJECTIVE 21 O BJECTIVE 21 As in other liquids, the attractions between water molecules are strong enough to keep them the same average distance apart, but they are weak enough to allow each molecule to be constantly breaking the attractions that momentarily connect it to some molecules and forming new attractions to other molecules (Figure 3.14). In other chapters, you will find this image of the structure of water useful in developing your understanding of what is happening when salt dissolves in your pasta water and when bubbles form in a soft drink or in a glass of Alka‑Seltzer and water. 105° O H H Space-filling model Ball-and-stick model Geometric Sketch H H O δ− δ+ δ+ H H O δ− δ+ δ+ δ− δ+ δ+ δ− δ+ δ+ Attraction between partial positive charge and partial negative charge 88 Chapter 3 Chemical Compounds Web Molecules
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3.3 Molecular Compounds 89 Figure 3.14 Liquid Water O BJECTIVE 22 Molecules break old attractions and make new ones as they tumble throughout the liquid. Attractions exist between hydrogen and oxygen atoms of different water molecules. 100 400 300 200 500 The Shockwave animation at the textbook’s Web site will help you to visualize the structure of water. S PECIAL T OPIC 4.1 Molecular Shapes, Intoxicating Liquids, and the Brain Even if we do not all have firsthand experience with alcoholic beverages, we all know that their consumption slows brain activity. Ethanol, or ethyl alcohol, is the chemical in alcoholic beverages that causes this change. H O C H H H C H H Information is transferred through our nervous system when one nerve cell causes the next nerve cell to fire. This firing is regulated by the attachment of molecules with specific shapes to large protein molecules that form part of the nerve cell’s membrane. When certain small molecules of the correct shape attach to the protein structures in the cell membranes, the cell is caused to fire. When certain other molecules attach, the firing of the cell is inhibited. For example, when a molecule called gamma‑aminobutanoic acid, or GABA, attaches to a protein molecule in certain nerve cells, it causes changes that inhibit the firing of the cell. C H O O C H H C H H C H N H H H The GABA molecules are constantly attaching to the protein and then leaving again. When the GABA molecules are attached, the information transfer between nerve cells is inhibited. Anything that would make it easier for the GABA molecules to attach to the protein would lead to a slowing of the transfer of information between nerve cells. Ethanol molecules can attach to the same protein as the GABA molecules, but they attach to a different site on the protein molecule. They change the shape of the protein in such a way that it becomes easier for the GABA molecules to find their position on the protein. Thus, when ethanol is present, the GABA molecules will become attached to the protein more often, inhibiting the firing of the cell. In this way, ethanol helps to slow the transfer of nerve information.
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  • Fall '06
  • Mark
  • Atom, atoms, Chemical bond

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