water_chemistry - ENVST 110 Water Chemistry Page 1 of 10...

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ENVST 110 Water Chemistry Page 1 of 10 Everything is made up of atoms. All atoms are made up of a nucleus with protons and neutrons that is surrounded by negatively charged electrons. Atoms are characterized by the number of protons. Atoms with the same number of protons may have different numbers of neutrons. These are called isotopes. For example, Carbon 12 (6 protons, 6 neutrons) and Carbon 14 (6 protons, 8 neutrons) are both isotopes of Carbon. Atoms can bond together to make molecules. If electrons are transferred from one atom to the other then the compound is called an ionic compound or salt. For example, what we know as table salt is Sodium Chloride, NaCl. If electrons are shared, then the bond is covalent. How electrons are distributed determines the molecules polarity. When electrons spend more time closer to one atom than the other, the result is a polar bond. This means one side of the bond is more negative than the other side of the bond. An ionic bond is basically the extreme case of this. If the sum of the bonds is a net polarity, then the molecule is polar. IMAGE SOURCE: "Chemistry in Context" Wm C Brown Publishers, Dubuque Iowa, 2nd edition, A project of the American Chemical Society, ed: A. Truman Schwartz et al., 1997, Chapter 5 "The Wonder of Water" http://witcombe.sbc.edu/water/chemistry.html Water is a good molecule to illustrate polarity. Because water has polar bonds within the molecule it can form weak bonds between molecules. We call these hydrogen bonds. http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/page3.html Hydrogen bonds give water properties that are important to life and the earth’s climate.
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ENVST 110 Water Chemistry Page 2 of 10 Cohesion: Molecules of liquid water “stick” together due to the hydrogen bonds. On the surface there are more connections to molecules on the interior and this creates a surface tension. Insects like water striders take advantage of this surface tension to walk on water. http://www2.uni-siegen.de/~fb08/abteil/pcii/image/strider.jpg Resist temperature change- requires more energy to move the molecules around because you have to break these weak hydrogen bonds. Temperature is just a measure of molecular movement- the higher the temperature the faster the molecules are moving. This is also why water boils at a higher temperature than expected based on its mass. Because water resists changes in temperature as energy is added it means that a large body of water like a large lake or the ocean can moderate temperature on a nearby landmass. You see this when costal areas are generally within a narrower temperature range than inland areas. For example, Santa Barbara stays reasonably cool during the summer and reasonably warm during the winter when compared to areas just inland. Water molecules in ice are farther apart than in liquid water. Ice floats on liquid water
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water_chemistry - ENVST 110 Water Chemistry Page 1 of 10...

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