OCNG 251 Brooks Spring 2013 Topical Study Guide for Exam 2 Chapters 5 7 Trujillo and Thurman 10th ed NOTE some of the material about climate change is in Ch 16 Ch 5 Water and seawater Atoms isotopes and molecules Atoms the basic building blocks of all matter o Resembles a microscopic sphere o Are composed of even smaller particles called subatomic particles Nucleus composed of protons and neutrons which are bound together by strong forces o Protons have a positive charge o Neutrons have no charge o Both protons and neutrons have about the same mass o Electrons surround the nucleus with have 1 2000th the mass of protons and neutrons The overall charge of most atoms is balanced because each atom contains an equal number of protons and electrons The number of protons distinguishes atoms from one another Ions when an atom loses or gains one or more electrons and thus has an overall electric charge Atoms can be represented as spheres of various sizes and the more electrons the atom contains the larger the sphere Covalent ionic and Gary US bonds A water molecule consists of a central oxygen atom covalently bonded to the two hydrogen atoms which are separated by an angle of about 105 degrees Covalent bonds due to the sharing of electrons between oxygen and each hydrogen atom o Both hydrogen atoms are on the same side of the oxygen atom o This curious bend of the water molecule is the underlying cause of most of the unique properties of water Water molecules are also polar to other polar chemical compounds o Can reduce the attraction between ions of opposite charges by as much as 80 Electrostatic attraction between oppositely charged ions produces an ionic bond Ionic bond this makes it easier for other molecules to separate o When the ions separate the positively charged ions become attracted to the negative ends of the water molecules the negatively charged ions become attracted to the positive ends of the water molecules o The process by which water molecules completely surround molecules is called times hydration Structure of the polar water molecule the hydrogen bond The bent geometry of water gives a slight overall negative charge to the side of the oxygen atom and a slight positive charge to the side of the hydrogen atoms Polarity the separation of charges gives the water molecule polarity o Causes water molecules to be dipolar two poles o Behaves as a tiny bar magnet o The polarity causes water molecules to orient themselves relative to one another Hydrogen Bond the positively charged hydrogen area of one water molecule interacts with the negatively charged oxygen end of an adjacent water molecule o Hydrogen bonds are much weaker than covalent bonds o Form between adjacent water molecules and stronger covalent bonds occur within the water molecule The anomalous properties of water Cohesion effect of hydrogen bonds being strong enough to cause water molecules to stick to one another o Causes water to bead up on waxed surfaces o Also give water its surface tension Results from the formation of hydrogen bonds between the outermost layer of water molecules and the underlying molecules Hydrogen bonds cause water to have the highest surface tension of any liquid besides mercury Because water molecules interact with other water molecules and other polar molecules water is able to dissolve nearly everything giving it the name the universal solvent High freezing and boiling temperatures High surface tension capillarity High latent heat capacity Expands when frozen Changes of state in water latent heats of melting and vaporization The attractive forces between molecules or ions in the substance must be overcome if the state of the substance is to be changed from solid to liquid or from liquid to gas o The attractive forces include hydrogen bonds and van der Waals forces Van der Waals forces are relatively weak interactions that become significant only when molecules are very close together as in the solid and liquid states but not the gaseous state o Very simply adding or removing heat is what causes substances to change their state Heat the energy transfer from one body to another due to a difference in temperature o Include both kinetic and potential energy Temperature the direct measure of the average kinetic energy of molecules that make up a substance Heat Capacity the amount of heat energy required to raise the temperature of a substance by 1 degree centigrade Specific Heat heat capacity per unity mass of a body called specific heat capacity is used to more directly compare the heat capacity of substances o Water has a high heat capacity because it takes more energy to increase the kinetic energy of hydrogen bonded water molecules than it does for substances in which the dominant intermolecular interaction is the much weaker van der Waals force Water s Latent Heat the amount of heat absorbed or released is due to water s high latent heats and is closely related to water s unusually high heat capacity Latent Heat of Melting the energy needed to break the intermolecular bonds that hold water molecules rigidly in place in ice crystals 80 cal Latent Heat of Vaporization the amount of heat that must be added to 1 gram of a substance at its boiling point to break the intermolecular bonds and complete the change of state from liquid to vapor gas 540 cal Latent Heats o 20 calories to raise ice from 40 to 0 degrees C o Latent heat of Melting 80 extra calories to cause ice to become liquid at 0 degrees C o 100 calories to raise water to 100 degrees C o Later heat of Vaporization 540 extra calories to turn liquid water into water vapor at 100 degrees C Heat capacity of land vs water impacts on climate Thermostatic Effect those properties of water that act to moderate changes in temperature which in turn affect Earth s climate o The Sun radiates energy to Earth evaporation removes this head energy and carries it to the atmosphere where it condenses and precipitate the releases the latent heat of condensation o Heat released when sea ice forms further moderates Earth s temperature The high heat capacity of water given it the ability to absorb the daily gains and minimize the daily losses of heat energy much more easily that land materials Marine Effect locations that experience the moderating effects of the ocean usually Continental Effect refers to areas less affected by the sea and therefore having a greater along coastlines or islands range of temperature differences Solutions and dissolving