Polarity Flashcards
rank the following from highest surface tension to lowest surface tension: Br2, HF, Hg
Br2 - lowest surface tensions because it is nonpolar covalent and is bonded by dispersion forces, which is the weakest type of bonds because they are temporary
HF - 2nd lowest surface tension because it is polar and has the ability to do hydrogen bonding because of the high EN difference. Hydrogen bonding is the strongest form of bonding because of the high EN difference
Hg - strongest surface tension because metallic substances have full charges and positively charged ions are attracted to the sea of electrons through electrostatic force
substances with stronger attractions have higher surface tension because particles pull together more strongly
dispersion < dip-dip < H-bonding < ionic and metallic
Explain why HCN has a much lower boiling point (about 1200C lower) than H2O
because water is polar and the atoms have a high EN difference, in order to boil it, you must break strong hydrogen bonds. In HCN, there are only weaker dipole-dipole bonds, which are easier to break than hydrogen bonds. Energy is required to break intermolecular bonds in order for a substance to boil, therefore the water would require more heat to boil because its attraction is stronger.
the stronger the force the more energy needed to break it.
Explain how it is possible for two non-polar covalent molecules to be attracted to each other
More electron density can be found on one side of the molecule. Thus, an instantaneous dipole forms. This dipole induces another dipole in a neighboring molecule (the e- are repelled to the other side). Now the two molecules attract due to partial charges. This attraction is only temporary
Why does NaCN have a higher boiling point than HCN?
NaCN is ionic, meaning strong ionic bonds must be broken. Ionic bonds are stronger because there is attraction between cations and anions’ full charges. In HCN, only weaker dip-dip bonds must be broken, thus requiring less energy because the stronger the force, the more energy it requires to break it. Ionic bonds are stronger than covalent bonds because there is attraction between full charges vs. partial charges.
would NaCN and HCN dissolve in water?
NaCN would dissolve in water because ionic NaCN has a similar polarity to very polar water. Water is strong enough to break apart the strong crystal lattice.
HCN would dissolve in water because polar HCN has a similar polarity to very polar water. Neg and pos ends of different mc’s would be attracted to eachother AND when mixed they could have a higher
entropy
network covalent substances
SiO2/quartz, diamond, and graphite
high melting/boiling point because they are connected by strong covalent bonds
describe the structure of diamond
strong covalent bonds between the carbon atoms in each layer
weaker forces hold the layers together
describe the structure of graphite
tightly packed crystal lattice
Should an aqueous solution of MgF2 conduct electricity? why or why not?
yes, because MgF2 is ionic. Thus, it consists of the ions, Mg+2 and F–. When MgF2 is dissolved in water, the water mc’s are attracted to the ions and they pull the ions out of the crystal lattice. Now all of the ions are free
to move, so the solution conducts electricity. (There are mobile charges in the solution.)
why does graphite conduct electricity
e- are loosely held in pi bonds because of sp2 hybridization, thus e- flow from p orbital to p orbital, creating a moving charge
delocalized e- are able to move freely through the p orbitals
hy is graphite a good lubricant?
Graphite consists of layers consisting of covalently bonded carbon atoms. However, there are only weak dispersion attractions between the layers. Thus, the layers are able to slide over each other. This makes graphite slippery, so it is a good lubricant.
why doesn’t diamond conduct electricity
The electrons are held tightly in the covalent bonds of the structure, so they are unable to move around. Thus, diamond cannot conduct electricity.
does sp3 hybridization
all of the valence e- are used to form localized covalent bonds
characteristics of water
- universal solvent because it is very polar so a lot of things can dissolve in it
- cohesive - surface tension/connected to itself
- high capacity for heat - able to stay a liquid for a wide range of temp
- density - is based on temp, expands when frozen
capillary action
attraction of the surface of a liquid to the surface of a solid
describe the structure of ice
hexagonal pattern to molecules get further away from each other
why does graphite have a high melting point
you must break very strong covalent bonds
why does diamond have a high melting point
you must break strong covalent bonds
why is diamond so hard and dense
the atoms are very close, and all of the bonds are covalent (tetrahedral)
why doesn’t diamond conduct electricity
e- are held tightly in the sigma bonds, therefore cannot move to create a moving charge to conduct electricity
