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46 Cards in this Set
- Front
- Back
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Inter-molecular forces
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attractions between molecules..always much weaker than attractions between atoms within molecules
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Intra-molecular forces
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are the chemical bonds that hold molecules together
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van der Waals forces
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are all the different kinds of intermolecular attractions…They all arise from attractions between opposite electrical charges
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Dipole-dipole Attractions happen because
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polar molecules such as HCl have partial +charge and - charge at opposite ends…unlike charges attract.....& polar molecules tend to line up so + of one is near - of other
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Dipole-dipole Attractions Thermal energy
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causes moleculs to collide and become distoriented ....alignment is not perfect..but there is a net attraction
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dipole dipole attractions are 1-4% weaker than covalent bonds b/c
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collisions lead to substantial misalignment of dipoles and bc attractions are only between partial charges
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Hydrogen bonds are Covalently Bonded to which very small, highly electronegative atoms mainly?
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flourine, oxygen, and nitrogen
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True or False Hydrogen Bonds are exceptionally Strong
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TRUE
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The Reason Hydrogen bonds are so Strong is b/c
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F-H,O-H, and N-H bonds are very polar and b/c the partial charges can get quite close b/c they are concentrated on very small atoms.
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Hydrogen bonds are typically How many times stronger than other dipole dipole attractions
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5 -10 times stronger
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When water freezes the molecules_____?
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become locked in place and each molecule participates in four hydrogen bonds
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True or False Frozen waters 4 hydrogen bonded structure occupies a larger volume than the same amount of liquid water making ice less dense than liquid
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True …that is why ice floats in water
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True or False Ice formation is responsible for erosion, causing rocks to split and creating potholes in cold city streets
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True
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Which hydrogen Bonds are found in our biological systems?
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N-H and O-H bonds ex. Proteins and DNA
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Hydrogen Bonding is also responsible for the ________ structure of DNA?
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Double Helix
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When noble gases and nonpolar molecules such as Cl2 and CH4 condense to liquid, and then crystallize into solids at low temps this is evidence that …
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Even Nonpolar substances experience intermolecular attractions
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If a substance can be condensed into a liquid or a solid then…
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attractions must exist to cause them to cling
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In 1930 who explained how the particles in nonpolar substances can experience intermolecular attractions?
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German physicist Fritz London
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True or False e- are constantly moving and they influence the movement of e- in neighboring particles
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TRUE
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London forces e- repel each other as an e- of 1 particle nears the other particle, e- of the 2nd are pushed away… how often does this happen?
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Continually as e- move around causing e- density to flicker back and forth
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London force -when at any given moment the e- density of a particle can be unsymmetrical: more neg. charge on one side than the other, this particle is called
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instantaneous dipole
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London force- An instantaneous dipole forms & causes e- density in its neighbor to become unsymmetrical too…the 2nd particle also becomes a dipole that is called
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and Induced dipole….b/c it was induced by the forming of the 1st
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London forces are short lived b/c
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the e- keep moving the dipoles vanish as quickly as they form…but they also reappear in a different orientaion with causes another dipole dipole attraction
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London forces short-lived dipoles cause…
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momentary tugs between the particles that when averaged overtime tend to bea weak net overall attraction
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London forces/dispersion forces are also called
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instantaneous dipole-induced dipole attractions
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True or False London forces exist between only nonpolar particles
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FALSE …London Forces exist between all molecules and ions
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London forces are the only kind of attraction between________ molecules.
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nonpolar
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Do London forces contribute to the total intermolecular attraction between polar molecules?
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YES…they significalty contribute where they're present in addition to regular dipole-dipole attractions
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Do London forces occur between oppositely charged ions?
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Yes…But they are relatively weak compare to ionic attractions…they add so little they are often ignored
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Boiling Point is a property that can be used to compare….
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the strenghts of intermolecular attractions.
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True or False…The higher the boiling point the stronger the attractions between molecules in the liquid.
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TRUE
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Polarizablity is…
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the measure of the ease with with which the electron cloud is distorted
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Polarizablity is also the measure of the ease with which the ______ and _______dipoles can form.
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Instantaneous & induced
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In General as the volume of the e- cloud increases, its polarizablity also______.
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increases
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When an e- cloud is large the outer e- are generally not held very _______ by the nucleus or nuclei
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Tightly…causing the e- cloud to be easily deformed so instantaneous and induced dipoles form without diffuclty
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True or False Large e- clouds experience stronger London forces than similar particles with small e- clouds
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TRUE
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Larger atoms have higher boiling points because of…
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increasingly stronger intermolecular attractions
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True or False For molecules containg the same elements, London forces DECREASE when more atoms are added.
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FALSE …London forces INCREASE when more atoms are added
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Molecules of the same # of atoms with a more compact shape have _______London forces than long chainlike structures of the same # of atoms.
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Weaker
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ion-dipole attractions happen when
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ions are able to attract the charged ends of polar molecules
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an example of ion dipole attractions in water is when…
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ionc compunds dissolve to give hydrated ions.
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In ion-dipole attractions Cations become surrounded by water molecules that are oriented with
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negative ends pointing toward the cation
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In ion-dipole attractions Anions become surrounded by water molecules that are oriented with
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positve ends pointing toward the cation
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Aluminum Chloride crystallize from water as a hydrate with this formula AlCl3 * 6H20 which element is the ion that the water attracts to?
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Aluminum Al3+ positivly charged …positive part of water is pointing out
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What are ion-induced dipole attractions…
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Ions that are capable of distorting nearby e- clouds, and creating dipoles in neighboring particles.
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ion- induced dipole attractions can be quite strong b/c…
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the charge on the ion dosent flicker on and off like instantaneous charges that start ordinary London forces
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