water and hydrogen bonding Flashcards
what are some roles of water?
homeostasis of the body, food absorption and digestion, elimination of waste and transport.
what are the properties of water?
melting point - 0 degrees
boiling point - 100 degrees
heat of vaporization - 2260 J/g
the enthalpy of water:
h20 (solid) –> h20 (liquid) enthalpy change = + 5.9 KJ/mol
h20 (liquid) –> h20 (gas) enthalpy change = +44.0 KJ/mol
what are enthalpy and entropy?
enthalpy is the total heat content in the thermodynamic system.
entropy is the degree of disorder in the same.
hydrogen bonds in water:
hydrogen bonds give water strong cohesive forces.
electronegativity of atoms
flourine - 4.0
oxygen - 3.4
nitrogen - 3.0
carbon - 2.6
hydrogen - 2.2
structure and shape of water:
water has a tetrahedral shape
tetrahedral shapes normally have a bond angle of 109 degrees, but the bond angle of water’s tetrahedral shape is 104.5.
it also contains hydrogen bonds and covalent bonds.
hydrogen bond has a bond dissociation of 23KJ/mol
covalent bonds has a bond dissociation of 470 KJ/mol
how is a water molecule polar?
v shaped molecule
it has an uneven charge distribution, oxygen is partially negative and hydrogen partially negative.
electric dipole which is the uneven distribution of charge
the forces are 10% covalent and 90% electrostatic
what is polar?
electrons are not shared equally
one part of the molecule is more negative that the other.
hydrophilic
what is non-polar?
electrons are shared equally
equally negative
hydrophobic
a liquid h20 molecule
a liquid molecule of h20 has 3.4 partners
hydrogen bonds formations
lifetime is 1-20 picoseconds
one break then another forms
formation 0.1 pico seconds
the structure of ice:
solid ice - h20 forms 4 hydrogen bonds
liquid ice - h20 forms 3.4 hydrogen bonds
liquid Is more dense than solid
ice - needs higher melting point and needs energy enthalpy.
h bonds and direction:
straight line bonds are strong
side bonds are weaker
what is an electrostatic reaction?
interaction between two charged molecules
what is a salt bridge?
ionic interactions usually occur between salts, usually two types of bonds. electrostatic and hydrogen bonds
what are van der waals forces?
made up of both attractive and repulsive forces
what are London disperse forces?
attractive forces
why do some compounds dissolve in water?
because of its polarity and its ability to form hydrogen bonds.
also because of electrolytes, they are molecules that dissociate to form ions.
why do some compounds not dissolve in water?
they are non polar molecules - hydrophobic (water fearing)
hydrophobic effect - elimination of non polar substances by water
hydrophilic:
dissolve in water
polar
entropy increases in water
attracts water molecules
hydrophobic
doesn’t dissolve in water
non-polar
entropy decreases In water
repels water molecules
what are amphipathic compounds?
compounds that contain polar and non-polar regions.
polar regions dissolve in water, while non polar regions avoid contact with water.
dispersion of lipids in H20:
Each lipid molecule forces surrounding h20 molecules to become highly ordred.
what are micelles?
an aggregate of amphipathic molecules in water. with the non polar portion in the interior and the polar portion in the exterior surface, exposed to water.
what are some examples of polar and non-polar amphipathic molecules?
polar- glucose
glycine
glycerol
non-polar - typical waxes
