Chapter 10 Flashcards
IMF
Inter molecular forces
-Forces of attraction
- Gas-weak
- Liquide-Moderate
- Solid-Strong
Intramolecular Force
Those that hold the atoms together within the molecule (covalent bonds)
Intermolecular forces
attractions between molecules
Three types of intermolecular forces in Pure substances
- London dispersion force
Dispersion Force
-Are present in all atoms & molecules
-Even molecules with no net dipole moment with have fluctuations in the electron distribution that result in an instantaneous or transient dipole moment
-As a transient dipole is established in one molecule it induces a dipole in all the surrounding molecules
-Induced dipoles cause attractive forces: dispersion forces
Strength of intermolecular forces
Can be measured by boiling point
Polarizability:
The ease with which the electron cloud can be distorted by neighboring charges
Dipole-Dipole Forces
- Only occur between polar molecules (with fixed net dipoles)
Dominates when comparing molecules of similar size
But for molecules of very different sizes, dispersion forces dominate-will probably not give us a question on it
Hydrogen Bonding
-Only if an H bonded to F,O, & N
-Very electronegative atoms is bonded with H is strongly pulls the bonding electrons toward it
- The H nucleus becomes exposed, acts as a very strong center of positive charge
-If another molecule has a F, O, N it will have a strong parctial negative charge
Format X-H-Y
X & Y must be F,O, or N
Dispersion Forces
the weakest, present in all molecules
✓Increase with increasing molar mass
✓Can be significant in large molecules
Higher boiling point for stronger forces
Ion-dipole forces
An attractive force that results from the electrostatic attraction between an ion and a neutral molecule that has a dipole.
There will be questions on ranking boiling point, intermolecular
Viscosity
he resistance of a liquid to flow
Stronger intermolecular forces →higher viscosity
You can look at the number of hydrogen bonds and what has bonds
Cohesive Forces
Cohesive forces: the forces that bind molecule to
each other in a liquid (IMFs)
✓because they have fewer neighbors, the surface
molecules are less stable (aka higher energy) than
those in the interior
✓leads liquids to minimize their surface are & minimize
interactions w/ surfaces
Surface Tension
Surface tension: the energy required to increase
the surface area by a given amount
✓ Water has a high surface tension due to its strong hydrogen bonds
Adhesive Forces
Adhesive forces: The IMFs between molecules of
a liquid and a solid surface are
✓If the adhesive forces are weak & the cohesive forces
are strong, the liquid will not “wet” the surface
✓When the adhesive forces are strong enough, the liquid
will “wet” the surface
Capillary Action
A liquid will climb up or down a narrow tube due to capillary action
Vaporization and Condensation
Some liquid molecules have enough kinetic energy to escape and be
a gas: vaporization or evaporation (liquid →gas)
- Some gas molecules have very little kinetic energy, therefore return
to liquid: condensation (gas →liquid) - Usually KE is lost to a surface (dust in clouds or condensation on a
glass).
Dynamic Equilibrium
Once the rates of vaporization and condensation are equal, total amount of vapor and liquid will not change:dynamic equilibrium
Vapor Pressure
- The pressure exerted by the vapor when it is in dynamic equilibrium with its liquid is the vapor pressure
- Liquids that evaporate easily are volatile
✓Weaker intermolecular forces → higher vapor pressure
✓Ethanol, gasoline, fingernail polish remover - Liquids that do not evaporate easily are nonvolatile
✓Stronger intermolecular forces → little or almost no vapor pressure
✓motor oil, antifreeze
All liquides exert a vapor at dynamic equilibrium
sublimation
phase change from a solid to a gas.
critical point
is the point at which two phases become indistinguishable from each other. It is found at the high-temperature extreme of the liquid–gas phase boundary.
supercritical fluid region
. A supercritical fluid is a region at which point distinct liquid and gas phases do not exist. It is found at the high-temperature extreme of the liquid–gas phase boundary.
the triple point
The triple point where the solid, liquid, and gas phases of CO₂ exist in equilibrium. It can be found at the intersection of the boundary lines for these phases.
phase diagram
combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. These diagrams indicate the physical states that exist under specific conditions of pressure and temperature, and also provide the pressure dependence of the phase-transition temperatures (melting points, sublimation points, boiling points).
crystalline solids
solids in which the atoms, ions, or molecules are arranged in a definite repeating pattern.
Usually Metals and ionic compounds
amorphous solids
The particles of such solids lack an ordered internal structure and are randomly arranged
Substances that consist of large molecules, or a mixture of molecules whose movements are more restricted, often form amorphous solids.
Ionic Solids
Ionic solids: consist of positive & negative ions held together by electrostatic forces (ionic bonds
✓Typically have high melting pts
✓Are hard but brittle
✓Don’t conduct electricity in solid state
➢but do in liq. state or solution
Metallic solids
Metallic solids: atoms held together by metallic bonds
✓“Sea of electrons” model
✓High thermal & electrical conductivity
✓Metallic luster
✓Are ductile & malleable
✓Many are hard & strong
Covalent Network Solid
Covalent network solids: atoms held together by covalent bonds, throughout
✓Very hard & strong
✓Have high melting pts
✓Don’t conduct electricity well
To ID you would need to know something about repeating patterns
Properties: very hard, not conductive, very high melting points
Molecular solids,
Molecular solids: composed of neutral molecules, held together by IMFs
✓Melting pts vary, but typically not very high
✓Many are soft & waxy
✓Don’t conduct electricity
are composed of neutral molecules. The strengths of the attractive forces between the units present in different crystals vary widely
Properties: variable hardness, variable brittleness, not conductive, low melting points
Boiling Point
Vapor pressure increases with temperature
When vapor pressure = external pressure (horizontal line), the liquid boils (that temp = boiling point)
The boiling point is dependent on the external pressure
✓ Higher external pressure → higher boiling point
✓ Lower external pressure →lower boiling point
Deposition
Gas to solid phase change
Supercritical Fluids
Above the critical point, the meniscus between the liquid and
vapor disappears and the states commingle to form a
supercritical fluid
✓ The temp. & press. of this are the critical temperature and critical
pressure
* Supercritical fluid have properties of both gas and liquid states:
✓ Fills confines of container (like a gas)
✓ Does not behave like an ideal gas
✓ Density more like that of a liquid
✓ But density increases continuously as the pressure is increased
Allotropes
Some elements can exist in multiple solid forms,
called allotropes
Crystal Defects
Crystalline solids can have defects
* Vacancy: place in the crystal struct. that is missing an atom/ion
* Interstitial site: an atom/ion occupies a site in between the usual sites of the crystal struct.
* Substitution site: one atom/ion in the crystal struct. is replaced by a diff. one (impurity)
✓ can be done intentionally (or naturally), altering the properties of the material: doping
Crystal Defects
Crystalline solids can have defects
* Vacancy: place in the crystal struct. that is missing an atom/ion
* Interstitial site: an atom/ion occupies a site in between the usual sites of the crystal struct.
* Substitution site: one atom/ion in the crystal struct. is replaced by a diff. one (impurity)
✓ can be done intentionally (or naturally), altering the properties of the material: doping
