Chapter 3- Water: The Matrix of life Flashcards
Briefly describe the molecular structure of water
- it is polar - O-H = polar because O is much more electronegative than H. The O has a partial negative charge and the H has a partial positive.
H2O us a polar molecule but why??
- because it has a dipole L> dipole - dipole interaction = electrostatic interaction…+ and -…aka hydrogen bond…very strong and its non covalent (doesnt share electrons ) - geometry : its bent at 104.5….one side = negative (O) and the other = positive (H) L> linear structures are non polar…because the polarity cancels out…ex: CO2 (OdoublebondCdoublebondO)
Electrostatic interactions occur between?
- opposite charges(including partial charges on atoms in a polar bond)
Since H2O is polar….what will dissolve in it?
- all polar molecules
What are the three types of non covalent bonding?
Ionic interactions Hydrogen bonds Van der waals forces L> Dipole-dipole, Dipole-induced dipole and induced dipole-dipole interactins.
Explain ionic interactions
- opposites attract - likes repel - forms salt bridges
Explain hydrogen bonding!
- occurs between a hydrogen that is attached to an oxygen or nitrogen and a lone pair of electrons on O, N or S - each H2O molecule can form H bonds with four other H2O molecules - these aggregations of bonds explain waters high boiling point…..it requires a lot of energy to break these bonds
Broadly what are van der waals forces?
- relatively weak electrostatic interactions - occur between neutral or permeant/induced dipoles/ L> magnitude depends on how easily an atom is polarized L> electroneg atoms with unshared pair of e- = easiest to polarize - the larger the electro diff between atoms = larger polarity of bonds..
Types of Van der waals forces: 1. Dipole-dipole interaction? 2. Dipole-induced dipole interaction? 3. Induced dipole-dipole
- between two molecules containing electroneg atoms….positive end is directed towards the negative end of another…these hydrogen bonds are very strong. 2. permanent dipole induces a transient dipole in another molecule via distorting its electron distribution. these are weaker than above. 3. motion of nearby electrons of non polar molecules results in transient charge imbalance in adjacent molecules. L> transient dipole in a molecule polarises the electrons of its neighbour..= london dispersion forces …these are the weakest (DNA molecule stacking ex)
Thermal properties of water?
- high melting and boiling points via hydrogen bonding - high heat of vaporization…it doesn’t boil easily - high heat capacity: water can absorb and store heat and release it slowly - organisms use hess to reg temp: high water content = easier time retaining heat via its high heat capacity and evaporation is used as a cooling system.
Polar molecules and ionic substances are hydrophilic/hydrophobic?
- hydrophilic (soluble in h2o)
Solvation spheres?
shells of h2o formed by water around a elute L> depends on charge density…the smaller and more highly charged the ion, the larger the salvation sphere L> an ion with a larger salvation sphere moves more slowly. - they negate the charges - this occurs when a salt is added to water
Hydrophobic molecules are polar/nonpolar?
nonpolar
Why do hydrophobic molecules group together in water?
- water molecules max the formation of H bonds with other water molecules and min any association with the non polar molecules….via forming small cages around a group of non polar molecules
Amphipathic molecules?
-contain both hydrophobic and hydrophilic ends - hydrophobic head and a long hydrophilic tail form micelles or bilayers
What is the formula for osmotic pressure?
L> describe what each variable is
π= iMRT
- π= osmotic pressure
- i= degree of ioniztion (van’t Hoff factor)
- M= molarity
- R= 0.082 Latm/kmol
- T= temperature in Kelvin…. C+2173)
