chem unit 3

what do strong IMFs (intermolecular attractions) have

• higher boiling/melting points

• lower vapor pressures

• higher viscosity

viscosity

how early liquid flows (highly viscous liquids flow slowly)

what are differentiating molecular characteristics responsible for different boiling points in different molecules

• bond/molecular polarity

• atomic radii

• shape/geometry

• number of electrons

polarizability

measure of how electrons in any atom, molecule, or ion are affected by (attracted/repelled) the presence of other atoms, molecules, or ions in their vicinity

induced dipole moment

when the presence of other charged regions polarizes a molecule, creating or strengthening an existing dipole

C because more electrons with the same size are easier to polarize electron clouds into regions

D because larger sizes with same elctron count make it more distortable

II because a larger sized molecule has electrons more spread out, weakly held, and easier to polarize

polarizability trend

generally increases with more electrons, greater atomic size, and a more exposed shape area

what happens to boiling points as polarizability increases

boiling point increases

dispersion forces

when two atoms or molecules get close together, the IMF interactions between electrons and protons induce instantaneous dipole moments (temporary polarization) that cause the particles to attract to each other

C because higher boiling points are based on dispersion (bigger sizes and electron counts)

A because high boiling points have low volatility/vapor pressure making CF4 the highest volatility

how to determine boiling points

• total number of electrons

• molecular size/shape and intermolecular contact area

• low bp=low dispersion

strong IMFs have…

bigger sizes with more electrons to achieve higher dispersion forces

which molecular orientation has higher dispersion interactions

A because of its flat and elongated geometry which is more polarizable

branching effect of IMFs

reduce effect contact areas over which molecules interact, decreasing IMFs

lower IMFS lead to…

• lower melting points, boiling points, and viscosities

• high volatilities

too much branching

how does molecular polarity influence IMFs

additional contribution through permanent molecular dipole moments (dipole-dipole forces) in the molecule leading to higher boiling points and IMFs

what would the graph look like for these

because 2 and 4 are polar you must use dispersion (size and electron count) as the baseline, then ADD the dipole moments for higher boiling points

A because more dispersion forces overcome the dipole leading to a higher boiling point

hydrogen bonding

an IMF polar (not covalent) bonding interaction between H and N, O, or F

polarizability summarization

dispersion

molecular polarity summarization

dipole-dipole

bond polarity summarization

hydrogen bonding

why is energy required to overcome IMFs smaller than to overcome a covalent bond

because it’s easy to break IMF but not bonds when boiling water

what do the configurations and potential energy of IMF interactions in mixtures look like

low potential energy (IMF interactions are strong) and more configurations (mixed particles have more options to adopt more states)

PEC diagram that always mixes

PEC diagram that doesn’t mix

PEC diagram that mixes slightly and more with higher temperatures

endothermic

energy taken in

exothermic

energy released

a.) will these mix

b.) endothermic or exothermic

c.) does mixing increase with temperature

• yes, mixing has lower PE and more configurations

• exothermic because PE is lowered which releases energy

• no, adding heat won’t improve miscibility because lower PE

No net energy change because temperature doesn’t change mixing

predict if th substances will mix and if they will mix more with increasing temperature

• won’t mix because unmixed has more configs

• won’t mix more with temperature because no net energy change means temperature has no effect

key ideas from molecular mixing

• competing IMFs influence PE change

• strong IMFs lead to good mixing and config options

• more configs lead to miscible mixtures

• molecules with similar IMFs are miscible

inter

between

intra

within

macromolecules

large molecules whose properties depend on functionality and structure

polymers

most common type of macromolecule that may be natural or synthetic; repeated units that are identical small pieces

monomers

make up polymers and are the repeating structural units connected by covalent bonds

addition polymerization

rearranging double bonds into single bonds

determine structural formula of the polymer and the molecular structure of the monomer

polymer formula - [CH2-CH-CH3]

monomer structure -

how to predict physical properties of polymers

• structure - length and shape (chain scale)

• composition - dispersion, polarity, H-bonding (IMF)

B because high meting points will be met with dispersion, dipole-dipole, and H-bonding

condensation polymerization

combining two different monomers and eliminating H2O by forming N-C or C-C bonds

polyamides

• combines a carboxylic acid (-CO2H) + amine (C-N-H)

• rugged and strong (nylon, Kevlar) – polar bonds and H-bonding

polyesters

• combines carboxylic acid (-CO2H) + alcohol (C-O-H)

• fabrics- can be spun with cotton, carpet – polar bonds

nylon

a polymeric silky material that can be processed into fibers, films, or shapes (combine diamine with dicarboxylic acid)

monomer structures

impact polymer physical properties because their functional groups are repeated along each polymer chain.

kevlar

a high strength polyamide (made from condensation) with many applications, from aerospace to body armor, has a stronger bond (not necessarily a chain) than nylon

why is kevlar stronger than nylon

kevlar has more hydrogen bonds and a rigid phenyl ring stacking and double bonds (nylon is more effective at dispersing energy)

C because it has an OH and Hydrogen bond which forms water making it soluble

little branching and longer chain lengths lead to…

• higher melting points, density, viscosity, and rigidity

• lower flexibility, elasticity, thermo-plasticity, and plasticity

• opposite response to lots of branching and short chain lengths

B because 2 has the most surface area and most effective dispersion forces

polymer crosslinking

tuning the properties of polymeric materials by adding other substances where one molecular species can act like a binder (H-bond or covalent bond) between chains which increases strength and rigidity

proteins

natural polymers made by the combination of smaller molecular called amino acid monomers

primary structure

unique sequences of amino acids in a protein

residues

side chains originating from different amino acid monomers

how to determine 3D structure in a protein

• backbond

• peptide bonds

protein folding

Intermolecular interactions with water molecules and intramolecular interactions between amino acid residues in a chain lead them to “fold” into structural conformations (secondary 3-D structures) that are most energetically stable in that environment.

secondary structure/like with like

the residues of similar types tend to segregate with each other and have an intramolecular fold

fatty acids

long chain (non-polar) hydrocarbons with a polar end group

saturated

hydrocarbon chains with no double bonds between carbons

unsaturated

hydrocarbon chains with at least one double bond

unsaturated fats configurations

• cis - same end

• trans - opposite ends

triglyceride regions

• heads work with water

• tails work with dispersion (connecting other chains)

ionic compounds

combination of metal and nonmetal atoms comprised of independent ions (no shared bonding electrons)

cation

positive ion (metal)

anion

negative ion (nonmetal)

• K-1e (4s lost) = Ar

• F+1e (2p gain) = Ne

• K+F = KF = potassium fluoride

ide

single nonmetal atom anion

ite

polyatomic ion with oxygen

ate

one more oxygen than polyatomic ion with oxygen

B

D because it has high pressure and tightly packed just like solid states are while maximizing density and attached to as many ions as possible

nitrate charge

NO3-

nitrite charge

NO2-

sulfate charge

(SO4)2-

sulfite charge

(SO3)2-

phosphate charge

(PO4)3-

phosphite charge

(PO3)3-

charge neutrality

an ionic network (usually solid) that forms no net charge

how does the transfer of electrons work across an ionic compound

from the metal to the nonmetal

C because ions with different charges (cations and anions) are closely associated while packed tightly together as a solid

properties of ionic compounds and ways to change properties

• don’t conduct electricity (melting can cause the ions to move freely)

• are brittle (rearranging ions to repel can make the crystal fall apart)

ionic compound physical properties

• solids with high melting/boiling points

• strong electrostatic forces

How would you expect the size of atom to change when they become cations or anions?

• cations are smaller than the atom they came from

• anions are larger than the atom they came from

based on coulomb’s law, when should forces be stronger

• with larger charges on the ions (q)

• with smaller sizes of the ions (radius)