Liquids, Solids, and Intermolecular forces Flashcards
Why are molecules attracted to each other?
intermolecular attractions are due to attractive forces btwn. opposite charges, such as cations and anions , - and + ends of polar molecules (H bonds especially strong).
Can nonpolar molecules ever have a charge?
yes, even nonpolar molecules will have a temporary charge
The larger the charge the _________ the attraction.
stronger
The smaller the charge the ________ the attraction.
weaker
If the bonds btwn. atoms in a molecule are very strong, how can the molecule be separated?
The stronger the attractions btwn. atoms or molecules the more energy is required to separate them
When liquid is boiling what is happening?
energy is being added to the point where the attractions between the molecules or atoms can be broken apart.
If a liquid has a high boiling point what can be said about the bonds btwn. the molecules or atoms that make up the liquid?
The higher the normal boiling point of the liquid , the stronger the intermolecular attractive forces.
How are nonpolar molecules able to sit next to polar molecules
Dispersion forces
What are dispersion forces?
fluctuations in the e- distribution in atoms and molecules that result in temporary dipole. The region with excess e- density has a small partial - charge and the region depleted of e- has a small partial charge of +
Attractive forces caused by temporary dipoles
Dispersion or London forces
Do all molecules and atoms have dispersion forces?
yes
Temporary Dipole vs. Permanent Dipole
Temporary dipoles are dipoles created by random e- dispersion, and permanent dipoles are found on polar molecules and are due to a dipole moment.
What happens when a temporary dipole is established in one molecule?
it induces a dipole in all the surrounding molecules, then the dipoles may attract
What does the size of an induced dipole depend on?
1) Polarizability of the e-
- volume of e- cloud
- the larger the molar mass the more e-, the more e- the larger the e- cloud, the bigger the cloud is the greater its polarizability, the greater the polarizability the stronger the attraction.
2) Shape of the molecule
- more surface to surface contact, the larger the induced dipole and the stronger the attraction
Dipole-dipole interactions involve _________ dipoles.
permanent
London dispersion involves _________ dipoles.
temporary
What does solubility depend on?
the attractive forces of the solute and solvent
what does “like dissolves like mean?”
miscible substances will dissolve each other and immiscible substances will dissolve each other but miscible substances will not dissolve immiscible substances.
polar substances will dissolve in _________.
polar solvents
what are the hydrophilic groups?
OH, CHO, C=O, COOH, NH2, and Cl
nonpolar molecules dissolve in ______ solvents.
nonpolar
What are the hydrophobic groups?
C-H and C-C
Many molecules have both ________ and ________ parts.
hydrophilic
hydrophobic
A dipole-dipole interaction where H is involved.
Hydrogen/ H bonding
How does H bonding happen?
A very electronegative element is covalently bonded to hydrogen, it hogs the electrons which makes it more negative. The Hydrogen atom has an exposed nucleus which is positive and attracts (e- clouds) negative molecules or molecule parts.
Which elements must be covalently bonded to H in order for a dipole-dipole to be called a “hydrogen bond?”
Fluorine, Nitrogen, or Oxygen
ex. O-H, N-H, F-H
What are the requirements for an H bond?
H must be attached to O,F or N and H must be directly involved in the bond.
Why are H bonds so strong?
Because they have a large polarity
Do C-H bonds like to interact with water?
No because water is polar and C-H is nonpolar
How many H bonds does water have when it is liquid?
3-4 H bonds
How many H bonds does water have when it is solid?
4 H bonds
How many possible H bonds can water have?
4
What happens when you introduce an ionic substance to a polar mixture?
ions are attracted to dipoles of polar molecule
What is one of the main factors that determines the solubility of an ionic compound in water?
the strength of the ion-dipole attraction. If there isn’t enough of an attraction ionic compound will be insoluble. I f the attraction weak in the compound it will be soluble.
Which has more force of attraction an i0n-dipole bond or a dipole-dipole bond?
they have the same force of attraction
Dispersion
present in all molecules
Has the lowest boiling point
temporary shift in charges causes domino effect
Dipole-dipole
present only in polar molecules
second to last in strength and boiling point
H bonding
Present in molecules where H is bonded to F, N or O.
middle strength wise and has midrange boiling point
Ion-dipole
Present in mistures of ionic and polar compounds
Strongest and has highest boiling point
Surface tension
the property of liquids that results from the tendency of liquids to minimize their surface area.
Why do liquids form spherical drops?
because spherical objects have less surface area
What are the factors that affect surface tension?
1) the stronger the intermolecular attractive forces the higher the surface tension will be
2) raising the temp of liquid reduces surface tension because raising the average temp of molecules will increase their movement
Viscosity
the resistance of liquid to flow, this results from strong intermolecular forces
the large the intermolecular attractions the greater the ____________.
viscosity
How can one reduce the viscosity of a liquid?
by increasing its temperature
Vaporization is an ______ process.
endothermic
molecules in a liquid are __________.
constantly in motion
when measuring temperature what is truly being measured?
the average kinetic energy
What happens during vaporization?
some molecules have more kinetic energy than the average, if the molecules are at the surface they may have enough energy to overcome attractive forces. Because of energy surface area is larger so evaporation occurs faster. Once molecules escape attractive forces they become a vapor
Condensation is an ___________ process.
exothermic
Describe what happens during the process of condensation.
some molecules of the vapor will lose energy through collisions, some molecules will collide into liquid and become a part of the liquid again, some may stick together and form droplets of liquid on surrounding surfaces
Dynamic equilibrium
When the rate of evaporation is equal to the rate of condensation; molecules are continually becoming vapors or droplets.
Vapor pressure
the pressure exerted by the vapor when it is in dynamic equilibrium with its liquid
The weaker the attractive forces the ____ ________ will be in vapor form.
more molecules
The weaker the attractive forces the weaker the ____________.
vapor pressure; the higher the vapor pressure the more volatile the liquid. * depends on temp
Boiling
when the temp of a liquid reaches a point where the vapor pressure is the same as the external pressure , vapor bubbles can form anywhere in the liquid (not just surface)
Boiling point
the temperature required to have the vapor pressure = external pressure
A higher elevation will cause a decrease in _________.
boiling point ; because less external pressure
What is normal boiling point?
the temperature at which the vapor pressure of the liquid is equal to 1 atm
the lower the external pressure the ____ the boiling point.
lower
Crystalline solids
solids that have their particles arranged in an orderly geometric pattern
ex. salt and diamonds
Amorphous solids
solids with particles that do not show a regular geometric pattern over a long range.
ex. Plastic and glass
