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This 5 page Class Notes was uploaded by Kelly Wetmore on Tuesday February 2, 2016. The Class Notes belongs to Bio 242 at University of Rhode Island taught by Barbara Van Sciver in Winter 2016. Since its upload, it has received 25 views.
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Date Created: 02/02/16
Wednesday, February 3, y Lecture 3 Valence Shell Review outermost shell = valence shell 1st 2 electrons 2nd 8 electrons 3rd 8 electrons An atom is most stable when its outer most shell is filled Ionic Bonds Ex: NaCL • Bonds are weak • Na gives up an electron to Cl and now has 11 protons and 10 electrons not electrically balanced anymore • Cl accepts an electron from Na and now has 17 protons and 18 electrons • Na has a full second shell and Cl has a full 3rd shell • NaCl falls apart in a solution because of the weak bond Cations positive charge Anions (electrolytes) negative charge 1 Wednesday, February 3, y Covalent Bonds Ex: CH4 (Methane) • Strong bonds • Do not fall apart in a solution • The 4 hydrogens each give up 1 electron to form electron pairs with the carbons outer shell • Both carbon and hydrogen now have their outer shell filled • Certain atom types have a stronger attraction than others Electronegativity O > N > C = H The greater the electronegativity = the greater the amount of electrons Polar v. Non-polar Polar • Covalent bonds that have electrons that are not shared equally • Molecules tend to be soluble in water • Hydrophilic Nonpolar (neutral) • Electron pairs are shared equally • Molecules are not soluble in water • Hydrophobic 2 Wednesday, February 3, y Water Primary biological solvent Around 75% of a cell’s volume is water Summing Up: 1. Covalent nonpolar 2. Covalent polar 3. Ionically Bonded substances Definitions Hydrogen bond • Bonds between a hydrogen and a nearby oxygen, nitrogen, hydrogen or chlorine Surface tension • Water has high surface tension Cohesion • The attraction for like molecules Adhesion • The attraction between 2 unlike molecules (usually a liquid and a solid) Diffusion • The movement of molecules from an area of high concentration of those molecules to an area of a low concentration of those molecules • Diffusion is the movement of molecules downhill • The more molecules in a high concentration = the faster the diffusion occurs to get to a lower concentration 3 Wednesday, February 3, y Osmosis • The movement of water from an are of higher concentration of water to an area of lower concentration of water through a semipermeable membrane Chemical driving force • High concentration > force is outward • Low concentration > force is inward Fick’s law of diffusion Concentration Gradient Permeability Surface area Molecular weight Distance Electrical Gradient There is a membrane between the ICF (intracellular fluid) and ECF (extracellular fluid) of a cell ICF • Negative • Inside of cell • Contains Potassium ions ECF • Positive • Outside of cell 4 Wednesday, February 3, y • Contains Sodium ions Electrochemical gradient wants positive in the membrane and negative out of the membrane Chemical Reactions Reactants (substrates) Products CO2 (g) + H2O (I) <——————————> H2CO3 (aq) 5
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