section 5.6—intermolecular forces & properties. imf’s and properties imf’s are...
TRANSCRIPT
Section 5.6—Intermolecular Forces & Properties
IMF’s and Properties
IMF’s are Intermolecular Forces London Dispersion Forces Dipole interactions Hydrogen bonding
The number and strength of the intermolecular forces affect the properties of the substance.
It takes energy to break IMF’sEnergy is released when new IMF’s are
formed
IMF’s and Changes in State
Some IMF’s are broken to go from solid liquid. All the rest are broken to go from liquid gas.
Breaking IMF’s requires energy.
The stronger the IMF’s, the more energy is required to melt, evaporate or boil.
The stronger the IMF’s are, the higher the melting and boiling point
Water
Water is a very small molecule In general small molecules have low melting and
boiling points Based on it’s size, water should be a gas under
normal conditions However, because water is polar and can form
dipole interactions and hydrogen bonding, it’s melting point is much higher
This is very important because we need liquid water to exist!
IMF’s and Viscosity
Viscosity is the resistance to flow Molasses is much more viscous than
water
Larger molecules and molecules with high IMF’s become inter-twined and “stick” together more
The more the molecules “stick” together, the higher the viscosity
Solubility
In order from something to be dissolved, the solute and solvent must break the IMF’s they form within itself
They must then form new IMF’s with each other
Solubility
- +
- +
- + - +- +
Solvent, water (polar)
+
-
- + Solute, sugar (polar)
Water particles break some intermolecular forces with other water molecules (to allow them to spread out) and begin to form new ones with the sugar molecules.
Solubility
Solvent, water (polar)
+
-
- + Solute, sugar (polar)
As new IMF’s are formed, the solvent “carries off” the solute—this is “dissolving”
- +
- +
- +- + - +
Solubility
If the energy needed to break old IMF’s is much greater than the energy released when the new ones are formed, the process won’t occur An exception to this is if more energy is added
somehow (such as heating)
Oil & Water
Water has London Dispersion, Dipole and hydrogen bonding. That takes a lot of energy to break
Water can only form London Dispersion with the oil. That doesn’t release much energy
Much more energy is required to break apart the water than is released when water and oil combine.
Water is polar and can hydrogen bond, Oil is non-polar.
Therefore, oil and water don’t mix!
Surface Tension
Surface tension is the resistance of a liquid to spread out. This is seen with water on a freshly waxed car
The higher the IMF’s in the liquid, the more the molecules “stick” together.
The more the molecules “stick” together, the less they want to spread out.
The higher the IMF’s, the higher the surface tension.
Soap & Water
Soap has a polar head with a non-polar tail
The polar portion can interact with water (polar) and the non-polar portion can interact with the dirt and grease (non-polar).
Polar head
Non-polar tailSoap
Soap & Water
The soap surrounds the “dirt” and the outside of the this Micelle can interact with the water.
The water now doesn’t “see” the non-polar dirt.
Dirt
Soap & Surface Tension
The soap disturbs the water molecules’ ability to form IMF’s and “stick” together.
This means that the surface tension of water is lower when soap is added.
The lower surface tension allows the water to spread over the dirty dishes.
What did you learn about soap?
Soap
Inter-molecular forces
Inter-molecular forces
Works based on
Molecular Geometry
Molecular Geometry
Bonding types &
Structures
Bonding types &
Structures
Determined by
Determined by