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23 Cards in this Set
- Front
- Back
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Water
Molecular Description |
Water is a complex structural compound composed of subunits
See pic. pg. 1 of blue sheets Actual structure of water is not know, but is a form of lattice HOH molecules are hydrogen bonded to each other |
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Water
Structure |
Ice - rigid lattice - each HOH molecule bonds to 4 other HOH molecules
Liquid water (near freezing)-each HOH is bonded to 3 HOH molecules Liquid water at boiling - H bonding is greatly reduced but still in a lattice |
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Water molecule
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Polar molecule - displays both positive and negative charges which interact with neighboring HOH molecules
Polarity is due to the shape if the molecule Oxygen in the HOH is the central atom and has 4 pairs of electrons - 2pairs are shared and 2 are unshared |
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Oxygen in the water molecule
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The unshared electrons have the greatest repulsive force and cause the shared electrons with H to shift to one side causing the bond angle to be 105
The result is a polar molecule called a dipole |
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Interaction between water molecules
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Dipole - when there is a n uneven distribution of valence electrons between the covalently bonded atoms of a molecule
Dipole-dipole interaction |
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Water Molecule
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Oxygen is very electronegtive compared to hydrogen
H bond is 10-12 times weaker than a covalent bond, but still strong enough to play a significant role |
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Role of Water in Biological Processes
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Chemical and physical processes of life require that molecules can move about
A fluid environment, wuch as water allows molecular mobility |
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Structure and Properties of Water
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Low molecular weight compound
Most low molecular weight compounds are gases at room temp and have much lower boiling points - water is liquid at room temp and higher boiling pint because of the H bonds |
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Structure and Properties of Water
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Ice - tetrahedral molecular lattice - each water molecule is hydrogen bonded to 4 others
This lattice partially breaks apart when ice melts |
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Structure and Properties of Water
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Unique property is liquid water is denser than frozen
Most Most substances are denser when frozen If Ice were denser than water, it would sink in lakes and oceans, and the earth woul become iced over |
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Water vs. Ice
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See pic on pg 6
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Water's Unusual Properties
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Molecular weight - 18g/mole (1 mole)
Density - 9gm/cm3 0.997 Boiling Point 100 C Freezing Point 0 C High Viscosity High Surface Tension High Dielectric Constant |
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Viscosity
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Defined as thickness of a liquid created by its intermolecular interaction
Thickness creates friction and increases resistance to flow |
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High Surface Tension
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H bonds account for high surface tension
Buoyancy |
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High Dielectric Constant
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Results from dipole character of the molecule
Reduces electrostatic forces between other charged particles Decreases the charge-charge forces between oppositely charged ions |
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Water as a Solvent
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Processes of life require a wide variety of ions and molecules to move about - be soluble in a common medium
Water serves as a universal intracellular and extracellular medium due to solvent ability Solvent ability from H bonds and dipole character Substances that dissolve easily in water are hydrophilic - water loving |
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Hydrophilic Molecules in Aqueous Solution
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Molecules that can form hydrogen bonds dissolve in water readily - many organic compounds such as hydroxyls compounds and amines; others such as aliphatic and aromatic hydrocarbons are not water soluble
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Hydrophilic Molecules in Aqueous Solution
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Water is a great solvent for ionic compounds such as NaCl
The dipoles of HOH interact with anions and cations and surround the ions with water - called hydration shells The high dielectric constant of water helps dissolve the ionic compounds |
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Hydrophobic Molecules in Aqueous Solution
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Hydrocarbons that are nonpolar and nonionic and cannot form hydrogen bonds can not easily dissolve in water
Hydrophobic molecules do not form hydration shells - instead they form clathrate (cage) structures around the nonpolar molecules |
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Hydrophobic Molecules in Aqueous Solution
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The clathrate structures causes a decrease in entropy, or randomness of the mixture
Decrease entropy - More order - molecules tend to cluster - cause of oil droplets |
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Amphipathic Molecules in an Aqueous Solution
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Both hydrophilic and hydrophobic
Fatty acids and detergents These molecules have a head group that is strongly hydrophilic and hydrophobic tail, usually a hydrocarbon chain see pg. 8 Form the basis of biological membrane bilayers that surround cells |
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Amphipathic Molecules in an Aqueous Solution
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The hydrophilic head gets immersed in water and the hydrocarbon tail lie in a parallel pattern and interact by van der Waals forces
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Micelles
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Spherical structures in amphipathic molecules
The polar head of the phospholipid molecule surrounded by water |
