Chapter 10 - Intermolecular forces Flashcards
Classify the intermolecular forces and bonding in CH3OH
London forces, dipole-dipole forces, and hydrogen bonding forces present, w/polar and nonpolar covalent bonds
London forces
“induced dipole moments,” electrons by chance all end up on the same side of an atom creating a negative and positive charge, attraction by electrostatic attraction
*the only IMF of nonpolar molecules and noble gases, more electrons = stronger attraction (ex. Xe>Ar in IMF)
*HEAVIER = stronger bonds bcz more electrons = more polarized when all of them are on one side
Dipole-dipole forces
- Polar covalent m’cules
- depends on MASS, heavier = stronger force
- RADIUS INCREASES forces by keeping dipoles within the molecule further from each other and thus polarizes
- reason why polar molecules dissolve each other
Hydrogen bonding
Two bonded molecules which contain H-N, H-O, and/or H-F (creates massive electronegativity difference, and bcz H is small the dipoles are closer). The differences in electronegativity, and thus hydrogen attraction (not technically covalently attached, more like magnetism than lego bricks) strengths depends on the type and how many of the bonds are present. (ex. molecules H-F = stronger attraction than those with H-O, more H-F > less H-F)
Rank the intermolecular bonding forces in order of weakest to strongest: dipole-dipole, London, hydrogen, ion-dipole forces
London, dipole-dipole, hydrogen, ion-dipole
Hydrogen bonding is responsible for water having a ____ shape when frozen and DNA to have a _____ shape and ______ proteins
- open-cage hexagonal shape
- Double-helix
- Fold
Ion-dipole forces
- Ions and polar compounds
- Coulomb’s law, higher charge = stronger attraction, small ions = more attraction
Factors impacted by IMFs:
INCREASES PROPORTIONALLY:
- melting/boiling point
- viscosity
- surface tension
- Heats of vaporization and fusion
- Solidity of state of matter
- Hardness
DECREASES PROPORTIONALLY:
- vapor pressure
What impacts intermolecular attraction?
charge difference (ion-dipole), amount/type of hydrogen bonds, molar mass (dipole-dipole and london dispersion), number of contact points (length of chain), radius/size
Is C-H-O a hydrogen bond? (IGNORE THIS SLIDE)
yes but its so weak that not rlly
Define volatile
Evaporates spontaneously
When does an increase in pressure result in a DECREASE in melting point? (leans to the left on a phase diagram)
Water
Define the triple point in a phase diagram
The point of pressure and temperature where all 3 states of matter exist in equilibrium (1/3 liquid, solid, and gas)
Define Hydration Sphere:
The surrounding of ions by water molecules, with the side facing the ion being oppositely charged
When do heavier molecules produce stronger IMFs? Why? What about lighter molecules?
- In dipole-dipole attraction, due to the internal dipoles of a molecule being further apart as the molecule is larger, and in London Dispersion, as heavier molecules have more electrons to polarize
- In ion-dipole attracting regarding the ion (ex. Li and H2O is stronger than Na and H2O bcz the Li radius is smaller)
Do alcohols evaporate easily? Why?
yes, as ethanol hydrogen bonds less than water
Molecules dissolve each other best with ______ IMFs
like (polar/ionic dissolves polar molecules and salts, nonpolar dissolves nonpolar, no interlap between polar and nonpolar)
What is the dominant IMF of KI(aq)?
Ion-dipole, it’s main interaction is with water, rather than other KI m’cules in a crystal lattice
Name the 3 INTRAmolecular forces
ionic, metallic, covalent
Describe the 3 steps an ionic solid goes through when dissolving in water:
- INTRAmolecular ionic bonds are broken
- INTERmolecular hydrogen bonds are broken
- INTERmolecular ion-dipoles are formed
What are london dispersion forces also known as?
van der waals forces/induced dipoles
Define capillary action
The spontaneous movement of a liquid up a narrow space due to strong IMFs and thus cohesion, adhesion, and surface tension (ex. the meniscus of water in a glass vial due to being extremely attracted to the glass)
Cohesive vs. adhesive
Cohesive: IMFs among m’cules in liquid
Adhesive: IMFs between liquid and surface
Define viscosity
The resistance to flow
Define Surface tension
Resistance to increases in surface area (ex. water bunching up into droplets)
Define amorphous solids
Solids that are irregular in their structure, irregular on the microscopic level (opposite of lattices and covalent networks)
Crystalline solids are _____ (more/less) abundant than amorphous solids
MUCH more
Types of crystalline solids:
- Ionic - Ions act as “lattice points,” held via ionic bonding
- Molecular - Molecules as the points, dipole-dipole or London Dispersion forces connect them
- Atomic (see other notecard)
Types of atomic solids
- Group 18/Noble gases - Noble gases connected by LDF
- Network solids - Covalent networks, Carbon and silicon atoms are the lattice points, creates networks as these covalent bonds prefer very specific orientations
- Metallic solids - Delocalized metal ions w/a “sea of electrons” moving from cation to cation
Define metal alloys
Metallic solids containing a mixture of elements. Overall has metallic properties.
Types of metallic alloys:
- Substitutional alloy - Main metal atoms replaced by other metal atoms w/similar size (ex. brass “host” = copper, but also 30% zinc)
- Interstitial alloy - Interstices/holes of structure occupied by small atoms. Increases hardness (ex. steel = iron crystal w/carbon in between the gaps)
Define dynamic equilibrium
Rate of change = rate of reverse change (ex. rate of condensation = rate of vaporization)
What is it called when a substance chnages from a solid to a gas? from a gas to a solid?
- sublimation
- deposition (sometimes also called condensation)
Normal melting point
Temp where solid and liquid states coexist at 1 atm
Normal boiling point
Temp. where vapor pressure of liquid = atmospheric pressure (thus boiling = being at 760 torr/mmHg)
Temperature _______ (can/cannot) change temperature and state at the same time
cannot
Define the “critical point” on a phase diagram
The end of the liquid-gas line (substance is a fluid, neither liquid nor gas)
Define critical temperature and critical pressure
Critical Temperature - Temperature AFTER WHICH vapor can no longer be liquified no matter the pressure
Critical Pressure - Pressure required to liquify at critical temperature
How do you find retention factor? (Rf)
Distance of substance/distance of solvent (ex. red distance/distance of water)
In what shapes does pure carbon exist in?
Graphite sheets and diamonds
https://docs.google.com/document/d/e/2PACX-1vRfGLHucxsABdbSajlZPhedqG8izbcJqBPMHKQaPr984iepOtbY6dn6XjJyoitIwBY5EN3cpLUBTAMf/pub
What is this process?
Distillation
Is the molecule HOCH2CH2CH2OH polar? How?
Due to the tetrahedral shape, every molecule in the chain is bent, resulting in a polar molecule
If an O-H exists in a NONPOLAR molecule, is it able to hydrogen bond?
no
What allows a solute to move up a piece of paper in chromatography?
Attraction to the solvent
How does greater attraction of a dye to the paper manifest in a chromatography experiment?
The dye does not move as far up with the solvent, getting stuck lower down on the paper.
