Transcript Document
Water the Universal Solvent Integrated Physics and Chemistry (9) Science Concepts. The student knows how solution chemistry is a part of everyday life. The student is expected to (A) relate the structure of water to its function [as the universal solvent]; +d +d H H 0 -d -d H2O is a special molecule. Each of the two hydrogen atoms shares one electron with the oxygen atom. Because the oxygen has a greater tendency to gain electrons, the electrons tend to spend more time near the oxygen end of the molecule. This gives the oxygen a partial negative charge and the hydrogen end of the molecule a partial positive charge. More Positive H H Think of him as a Polar Bear or Sticky Mickey 0 More Negative Because of this, water has polar covalent bonds. It is a Polar Molecule or a dipole (a molecule with a positive and negative pole). It will make weak bonds with other polar molecules. Opposite ends of the molecules attract! The hydrogen end of the water molecule can also make hydrogen bonds with the oxygen, nitrogen, or fluorine end of other molecules. Hydrogen Bonds http://www.stolaf.edu/people/giannini/fl ashanimat/water/water.swf • Nonpolar molecules do not have positive and negative ends. Oil, wax, and gasoline are common nonpolar substances. • Think about oil and water. The bonds within an oil molecule consist of pairs of electrons that are shared pretty equally between the participating atoms. Oil in a nonpolar molecule. A nonpolar molecule does not dissolve in water because it is not attracted to the polar water molecule. + - This is how water easily breaks apart ionic compounds. It surrounds both negative and positive ions and breaks apart ionic solids. http://www.chem.iastate.edu/group/Greenbo we/sections/projectfolder/flashfiles/thermoche m/solutionSalt.html For this reason, water is called the Universal Solvent! The positive end of the water molecule attracts to the anion (negative ion) and the negative end of the water molecule attracts to the cation (positive ion). 5 The diagram on the right shows water molecules and ions from an NaCl crystal. What is the most likely reason that each water molecule is arranged so that the oxygen part of the molecule faces a sodium ion? A The oxygen in a water molecule contains a partial negative charge. B Gravity rotates the oxygen atoms to face the more-massive sodium ions. C Hydrogen atoms create repulsive forces with chloride ions D Oxygen atoms form covalent bonds with sodium ions. 1. What is the question asking? 2. Look at your diagram!!! The answers may be there. Sodium has a positive charge. If you don’t know the name of a chemical, use your periodic table! 3. Remember the Structure of water!!! The oxygen end of the molecule has a partial negative charge! It will be attracted to the sodium. You have been given a water molecule. Let’s play… 1. Simon Says: Hydrogen bond with two of your neighbors. 2. Simon Says: Point the correct end of your water molecule to this ion: Na+1 3. Simon Says: Point the correct end of your water molecule to this ion: Cl-1 4. Simon Says: Point the correct end of your water molecule to this ion: SO4-2 5. Simons Says: Point the correct end of your water molecule to this ion: Ca2+ 6. Point the correct end of your water molecule to this molecule. CCl4: Water won’t be attracted to something non-polar and uncharged!