4. Non-Covalent interactions Flashcards
How are ions formed? What is the result?
Which are stronger? Covalent bonds or electrostatic interactions?
Produced when electrons are transferred from one atom to another atom
Result: Positive and negative ion, held together by electrostatic interaction which is a non-covalent interaction
Covalent bonds, but many more non-covalent bonds can form
What are electropositive elements?
What are electronegative elements?
Tend to lose electrons e.g. metals
Tend to gain electrons
What is polarisation?
When the distribution of electrons in covalent bonds is not equal between the two atoms.
Existence of polarisation= Makes electrostatic interactions possible when compound does not form ions e.g. Water
Electronegative atoms= Attract electrons more= End which is relatively negative
The more electropositive an element, the more reactive it is
What are dispersion forces? How strong are they?
Fluctuations in electron clouds which allow molecules to interact via instantaneous dipoles in neighbouring molecules
Induced dipoles then attract one another
Fluctuations in adjacent electron clouds
They are the weakest electrostatic interaction
What do short range forces depend on?
The interacting atoms being the right distance apart
Too far: Cannot interact
Too close: Electron clouds overlap and they repel
What do covalent bonds do to the shape of the molecule? What do non-covalent interactions?
Covalent: Framework shape of molecule
Non-covalent: Actual shape determined
What are hydrogen bonds based on?
What are some properties of hydrogen bonds?
Polarisation of hydrogen atoms with electronegative atoms
Have properties which fall in between those of covalent and non-covalent interactions
Directional (of defined length) like covalent bonds
Lower in energy than covalent bonds but higher than non-covalent
Both donor and acceptor atom must be electronegative
Why is water solid at temperatures far above what would be expected?
Water can form strong hydrogen bonds with itself, ice contains a rigid lattice of molecules in its crystal structure, held together by hydrogen bonds
Why are ionic compounds often soluble in water?
What has to happen to the overall free energy of the system for a compound to dissolve?
Polar water molecules can form energetically favourable interactions with free ions= Charge-dipole attraction
Must decrease
Overall free energy: Compound + Solvent
Why are non-polar organic compounds often insoluble in water?
Why are polar organic compounds often soluble in water?
Non-covalent interactions between water and compound are limited
Water molecules able to form a ‘cage’ around the compound
This decreases entropy of system= Free energy increases= CANNOT DISSOLVE
Polar= Formation of dipole-dipole and hydrogen bonding interactions between water molecules and compound
This decreases free energy= favourable
Free energy decrease must be greater than the increase caused by disrupting hydrogen bonding networks already between molecules of the compound
What do the solubility of compounds depend on?
Balance between the carbon skeleton (insoluble) and functional groups which may form favourable interactions with water= soluble
Balance between favourable and unfavourable interactions with water molecules determines solubility
What is the hydrophobic effect?
Unfavourable interaction of non-polar molecules with water molecules
Pushes non-polar molecules together in aqueous solution= Form big blob in the middle= Droplets and water molecules surround big blob
Major factor in determining protein structure
What is hydrophilic?
What is hydrophobic?
What is amphipathic?
Hydrophillic= Water loving, soluble polar molecules
Hydrophobic= Water hating, insoluble non-polar molecules
Amphipathic= Compounds which contain parts that are hydrophobic and hydrophillic
