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
