CHEM 162 EXAM 2 QUESTIONS AND
ANSWERS
Hydrogen Bonding - Correct Answers -A special type of dipole-dipole interaction that
occurs only in molecules that contain H bonded to a small, highly electronegative atom,
such as N, O, or F.
- which have lone pairs (let's call these atoms $ or €).
These H−$ bonds are very polar.
-The partially positive H atom from one unit is attracted to the partially negative $ atom
from another unit (or to another partially negative atom, €). This is the hydrogen bond.
Even though the strength of one H bond may be small, - Correct Answers -the
combined strength of many H bonds may be large
water has - Correct Answers -particularly strong hydrogen bonding intermolecular forces
hydrogen bonding is strong enough - Correct Answers -to survive even in the vapor
phase.
Boiling Points, Vapor Pressures, Viscosities, and Surface Tensions - Correct Answers -
are all determined by Intermolecular Forces
Stronger intermolecular forces - Correct Answers -require more energy to disrupt
intermolecular interactions
Predicting the Types and Relative Strengths of Intermolecular Forces: - Correct
Answers -Remember:
a) Bonding forces are stronger than intermolecular forces.b) Hydrogen bonding is a
strong type of dipole-dipole force.c) Dispersion forces are decisive when the major
difference is molar
mass or molecular shape.
solids - Correct Answers -• Less thermal energy available
•Less motion of the molecules
•More ordered spatial properties
The smallest repeating unit needed to describe the complete extended structure of a
crystal (through repetition and translation). - Correct Answers -unit cells
, How do we know what crystals look like?
x-ray diffraction - Correct Answers -To satisfy the diffraction conditions, the wavelength
of light needs to be comparable to the unit cell dimensions Ångstrøms (10^-10meters)
3 Types of Crystalline Solids - Correct Answers -molecular, ionic, atomic
Atomic Solids - Correct Answers -e.g. all metals, Si, Carbon (diamond, graphite)
Ionic Solids - Correct Answers -e.g. salts like NaCl
Molecular Solids - Correct Answers -e.g. protein crystals, sucrose
Metals in solids can be treated as hard spheres that (usually) pack in a way to minimize
the empty space between spheres. - Correct Answers -closest packing.
a cubic structure, and a hexagonal structure - Correct Answers -Two distinct structures
can be formed by closest packing of atoms-
Cubic: x = y = z - Correct Answers -All unit cell angles = 90°
Hexagonal: x = y ≠ z - Correct Answers -some unit cell angles
≠ 90° (60° or 120° instead)
Packing Efficiency - Correct Answers -The fraction of the volume (often expressed as
%) of the unit cell that is occupied by atoms, ions, or molecules
Example: the face centered cubic unit cell
Phase Changes for Water, and their Enthalpies - Correct Answers -gas, liquid, solid
The pressure of the vapor at equilibrium is called theVapor Pressure, Pvap, of the liquid
(or solid) - Correct Answers -At equilibrium, Rate of Evaporation = Rate of
Condensation
∆H°vap = - Correct Answers -standard enthalpy of vaporization (or standard heat of
vaporization)
• if Pvap is large substance called "Volatile" • as intermolecular forces increase, Pvap
decreases
Phase Diagram Landmarks - Correct Answers --Phase boundary lines
-Triple point
-Critical temperature
-Critical pressure
-Critical point
ANSWERS
Hydrogen Bonding - Correct Answers -A special type of dipole-dipole interaction that
occurs only in molecules that contain H bonded to a small, highly electronegative atom,
such as N, O, or F.
- which have lone pairs (let's call these atoms $ or €).
These H−$ bonds are very polar.
-The partially positive H atom from one unit is attracted to the partially negative $ atom
from another unit (or to another partially negative atom, €). This is the hydrogen bond.
Even though the strength of one H bond may be small, - Correct Answers -the
combined strength of many H bonds may be large
water has - Correct Answers -particularly strong hydrogen bonding intermolecular forces
hydrogen bonding is strong enough - Correct Answers -to survive even in the vapor
phase.
Boiling Points, Vapor Pressures, Viscosities, and Surface Tensions - Correct Answers -
are all determined by Intermolecular Forces
Stronger intermolecular forces - Correct Answers -require more energy to disrupt
intermolecular interactions
Predicting the Types and Relative Strengths of Intermolecular Forces: - Correct
Answers -Remember:
a) Bonding forces are stronger than intermolecular forces.b) Hydrogen bonding is a
strong type of dipole-dipole force.c) Dispersion forces are decisive when the major
difference is molar
mass or molecular shape.
solids - Correct Answers -• Less thermal energy available
•Less motion of the molecules
•More ordered spatial properties
The smallest repeating unit needed to describe the complete extended structure of a
crystal (through repetition and translation). - Correct Answers -unit cells
, How do we know what crystals look like?
x-ray diffraction - Correct Answers -To satisfy the diffraction conditions, the wavelength
of light needs to be comparable to the unit cell dimensions Ångstrøms (10^-10meters)
3 Types of Crystalline Solids - Correct Answers -molecular, ionic, atomic
Atomic Solids - Correct Answers -e.g. all metals, Si, Carbon (diamond, graphite)
Ionic Solids - Correct Answers -e.g. salts like NaCl
Molecular Solids - Correct Answers -e.g. protein crystals, sucrose
Metals in solids can be treated as hard spheres that (usually) pack in a way to minimize
the empty space between spheres. - Correct Answers -closest packing.
a cubic structure, and a hexagonal structure - Correct Answers -Two distinct structures
can be formed by closest packing of atoms-
Cubic: x = y = z - Correct Answers -All unit cell angles = 90°
Hexagonal: x = y ≠ z - Correct Answers -some unit cell angles
≠ 90° (60° or 120° instead)
Packing Efficiency - Correct Answers -The fraction of the volume (often expressed as
%) of the unit cell that is occupied by atoms, ions, or molecules
Example: the face centered cubic unit cell
Phase Changes for Water, and their Enthalpies - Correct Answers -gas, liquid, solid
The pressure of the vapor at equilibrium is called theVapor Pressure, Pvap, of the liquid
(or solid) - Correct Answers -At equilibrium, Rate of Evaporation = Rate of
Condensation
∆H°vap = - Correct Answers -standard enthalpy of vaporization (or standard heat of
vaporization)
• if Pvap is large substance called "Volatile" • as intermolecular forces increase, Pvap
decreases
Phase Diagram Landmarks - Correct Answers --Phase boundary lines
-Triple point
-Critical temperature
-Critical pressure
-Critical point
