Ch.2 aqueous chemistry Flashcards
Water shape and bond type
-Water forms covalent bonds, H bonds, and has a tetrahedral shape.
-The central oxygen atom forms covalent bonds with the two hydrogen atoms thus leaving a pair of unshared electrons on the oxygen.
Water and polarity
-Water is polar due to the difference in electronegativity between oxygen and hydrogen. (i.e. uneven distribution of charge) Water also forms a dipole between oxygen and hydrogen.
- Water also dissolves polar solvents
H bonding in H2O
-Water forms four hydrogen bonds because it has two hydrogens atoms to donate to a hydrogen bond and two unpaired electrons to accept a bond.
- This is considered an electrostatic interaction
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Structure of ice and H bonds
- In ice, which is a solid crystalline structure of water, each water molecule forms hydrogen bonds with four other water molecules. (I.E acting as a donor for two h bonds and an acceptor of two h bonds)
-Once the ice melts this structure begins to break down.
H bonding and liquid water
- Water forms H-bonds with up to four other water molecules, but each bond has a lifetime of 10-12.
- Due to water’s ability to form H bonds, it is highly cohesive allowing for it to have high surface tension. (i.e. insects walking on water)
H bonds and other molecules
-Hydrogen bonding can form not only between water but also with other compounds that bear N and O functional groups.
-This is due to N-H and O-H being hydrogen donors and the electronegative N, O and sometimes S atoms acting as hydrogen acceptors.
- Hydroxyl groups (O-H) and Amine groups (N-H) (functional groups)
H- bonds and DNA
- H bonds make DNA a Stable molecule this is because the complementarity bases of DNA are determined by their ability to form h bonds with each other.
I.e. in Cytosine and Guanine 3 N-H groups are H bond donors and N-O atoms are acceptors.
Van Der Waals Interactions
-are electrostatic interactions and are usually weaker than hydrogen bonds.
- Van der waals interactions and hydrogen bonding are individually weak molecules that contain multiple groups that are capable of participating in intermolecular interaction
Dipole- Dipole interactions
- is the interaction between two strongly polar groups (induced dipoles ) and has the strength of about 9 kj/mol
- considered weak interactions
London dispersion forces
- weak interactions that occur between nonpolar molecules as a result of small fluctuations in their distribution of electrons that create a temporary separation of charge i.e methyl groups
Dielectric constant and water
- Dielectric constant is a measure of a solvents ability to diminish the electrostatic attractions between dissolved ions. The higher the Dielectric constant of the solvent the less the ions are able to associate with each other
- Water dissolves many compounds i.e ionic due to its high dielectric constant.
-ionic compounds i.e Nacl which water surround the ions and align their partial charges with the oppositely charged ions.
Water and glucose
-Water dissolves polar compounds such as glucose because multiple h bonds can be formed.
- Glucose has six h bonding oxygens and is considered to be highly soluble
What happens when oil and water mix
- A nonpolar molecule is hydrated by water and the system loses entropy
- The loss of entropy presents a thermodynamic barrier to the hydration of a non polar molecule. (i.e a layer of constrained water molecules)
The hydrophobic effect
- is the phenomenon by which nonpolar molecules aggregate to avoid contact with water. ( i.e. the exclusion of non polar substances from an aqeous solution)
- When adding more nonpolar molecules they tend to aggregate and the entropy of the system increases.
- The hydrophobic effect governs the functions of many biological molecules and structures.
Hydrophillic interactions
- water-loving, glucose and lipids along with other hydrating substances are considered hydrophilic
