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Biol 1201 - Biol 1201 1-13 1-15 What determines the number...

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Biol 1201 1-13 … 1-15 What determines the number and type of chemical bonds? Number = Valence Type = Electronegativity Electronegativity Electro. Is a measure of the tendency of an atom to attract a bonding pair of electrons Measure of the attraction an atom has for electrons Chemical Bonds Forces holding atoms together in molecules Characterized as Strong or Weak depending on the energy required to make/break the bond Strong o Covalent bonds involve sharing of electrons Weak o Non-covalent bonds Ionic interactions – attraction of opposite charges. One atom donates an electron to another Hydrogen bond b/w partially charged atoms Valence vs. Valence Electrons Valence is the number of electrons needed to fill the outermost shell of an atom Valence electrons are the electrons contained in the outermost electron shell of an atom Moles and Molar Concentrations 1 mole = the mass of a substance equal to its gram molecular weight 1 molar solution = a solution containing 1 mole of a substance per 1 liter of solution Can you have a 1 molar solution of insulin? 5.727 kg/liter 1 kg/liter is the density of dry protein So no you can’t Ionic Bonds Weak bond Transfer an electron from one atom to another Covalent Bonds Strong bond Sharing of an electron b/w two atoms Polar Bonds Unequal sharing of electrons Partial pos. and partial neg. regions No net charge Hydrogen Bonds Weak (non-covalent) bonds B/w partial pos. and partial neg. charges Water 70 to 90 percent of weight of most life forms is water Sets the lower temp limit for life Possibly sets the upper temp limit? (Probably not)
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Important role in structures and properties of biological molecules Water is a biological molecule The unusual properties of water Result from hydrogen bonding Water behaves as a much larger molecule Bonds Covalent: H-O 110 kcal/mole Weak (hydrogen bond): 4.5 kcal/mole o H bonding effectively makes water a larger molecule o In ice a water molecule interacts with exactly 4 other water molecules o In liquid water, on average 3.6 or fewer other molecules (can be made and broken very quickly) Small molecules – a comparison of properties Water: o Boiling point 100 C o Melting point 0 C Ammonia: o Boiling point 35 C o Melting point -77 C Ethanol: o Boiling point 78.5 C o Melting point -117.3 C Unusual properties of water o High heat capacity o High heat of vaporization o High heat of fusion o Most dense at 4 C o High dielectric o Capillary action and surface tension o Ionization Heat capacity Amt of heat to raise temp of 1g of water by 1 C 1 cal /g of water Heat of vaporization Amt of heat to vaporize 1g of water 540 cal/g at 100 C Heat of fusion Amt of heat removed to freeze 1g of water 80 cal/g Water most dense at 4 C B/c of the hydrogen bonding structure, ice is lighter than water Lakes don’t freeze from bottom up High dielectric Good solvent 1-20
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