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Properties Based on Bonding |
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Definition
| Not all ionic compounds are soluble, but those containing ammonium ions, nitrate ions, and alkali metal ions are.[image] |
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Definition
| The increased number of oxygen atoms pulls negative charge away from the O-H bond, weakening the attraction of the proton for the electron pair and thus strengthening the acid. |
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Binary Acid Strength
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Definition
The greater the size of the negative ion, the weaker its attraction for the proton, and so the stronger the acid, and the weaker the conjugate base. HI is the strongest binary acid.
Strong Acids: HCl, H2SO4, HNO3
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Kinetic Molecular Theory-
particles of matter constantly in motion
increase temperature--increase speed |
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Definition
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Definition
IF the temperature is not changed, no matter what else is listed in the problem, the average kinetic energy of a gas does not change. That is the definition of temperature!
All gases begin to act non-ideally (aka real) when they are at low temperatures and/or high pressures because these conditions increase particle interactions
Under the same conditions, the stronger the intermolecular attractions between gas particles, the LESS ideal the behavior of the gas |
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Properties of a Gas
What is the effect of changing moles, pressure, and temperature of a gas? |
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Definition
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Ideal Gas Law
PV =nRT
R=0.0821 L*atm/mol*K
K=oC+273
1atm=760torr=101.3kPa
1L=1000mL
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Definition
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Dissolving/Dissociation: Solute and Solvent
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Definition
When drawing solute ions:
Pay attention to size (Na+ is smaller than Cl-)
Draw charges on ion, but not on water
Draw at least 3 water molecules around each
The negative dipole (oxygen side) points toward cation and the positive dipoles (H side) points towards the anion |
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Term
Question:
Rank the solutions in order of increasing molarity.
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Definition
Answer:
C,D, and E (tied)-lowest concentration
(4 solute particles/50mL and 2 solute particles/25mL)
A and F (tied)
B-most concentrated (12 solute particles/50mL) |
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London Dispersion Forces
weakest IMF
affects boiling point and melting point |
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Definition
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Term
Question:
Which of the following would have the highest boiling point?
A: He
B: Ne
C: Xe
D: Kr |
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Definition
Answer:
Xenon
All are nonpolar gases. The only IMF are LDF. The strength of LDF are determined by the polarizability of the atoms. The atom with the greated number of electrons will be the most polarizable, having the strongest IMF and the highest bp.
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Deviations from Ideal Gas Behavior
Think about KMT
- completely elastic collisions
- no IMF
At low temperatures and high pressure, those statements are not true |
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Definition
At which temperature and pressure will nitrogen gas behave least like an ideal gas?
A. 100K, 100atm
B. 100K, 1atm
C. 700K, 0.1atm
D. 700K, 1atm
Least ideal at low temperature, high pressure: A |
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Hydrogen Bonding
Stongest IMF
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Definition
Hydrogen bonding is seen in the following molecules: water, DNA, ammonia, HF, and alcohols. H-bonding is an attraction or force between molecules
Hydrogen bonds are like a sandwich with N, O, and/or F as the bread. H will be in a intramolecular (same molecule) bond with one N, O, and/or F and have an intermolecular attraction (different molecule) with the other.
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Coulomb's Law and Solubility
Ionic compounds can dissolve in polar liquids like water because the ions are attracted to either the positive or negative part of the molecule.
There is a sort of tug-of-war involved with species dissolved in water. The water pulls individual ions away from the solid. The solid is pulling individual ions back out of the water. There exists an equilibrium based on how strongly the water attracts the ions, versus how strong the ionic solid attracts the ions.
We can predict the degree of solubility in water for different ionic compounds using Coulomb's law. The smaller the ions, the closer together they are, and the harder it is for the water molecules to pull the ions away from each other. The greater the charge of the ions, the harder it is for the water to pull them away as well.
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Definition
QUESTION:
Predict which of the following pairs should be more soluble in water, based on Coulombic attraction.
LiF or NaF
NaF or KF
BeO or LiF
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Entropy in Solutions (chaos)
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Definition
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Polar molecules-have permanent dipole moments
Nonpolar molecules-have no NET dipole moment
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Definition
Which of the following would have the highest vapor pressure at 25oC?
A. H2O
B. Hg
C. CCl4
D. C10H22
C: CCl4 has the highest vapor pressure because it has the weakest IMF. The smallest nonpolar molecule will generally have the weakest IMF. (Yes, the C-Cl bond is polar, but there is no NET dipole moment.) |
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Bonding and Electronegativity
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Definition
Differences in electronegativities lead to different types of bonding*:
0.0 – 0.4: Bond is generally considered nonpolar
0.5 – 1.7: Bond is generally considered polar
> 1.7: Bond is generally considered ionic |
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Term
Question:
Which bond would be the most polar?
A. C-O
B. H-O
C. H-F
D. F-O |
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Definition
Answer:
H-F has the greatest electronegativity difference between the two atoms. Atoms that are far apart on the periodic table will have the greatest difference in electronegativity. Remember, C-H bond is essentially nonpolar. There is very little electronegativity difference in C and H atoms. |
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Definition
Ionic compounds are soluble in water, have high mp and bp, and are brittle. As the crystal is struck, the ions become displaced. The displaced ions will repel like charges and fracture.
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Lewis Diagrams/VSEPR
Question:
Which of the following molecules has a tetrahedral shape?
A. NH3
B. H2O
C. BH3
D. CH4 |
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Definition
Answer:
CH4. Tetrahedral molecules must have 4 bonds and no lone pairs of electrons on the central atom. |
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Ionic or Covalent?
What are the bonding tests? |
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Definition
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Term
Question:
Why is the melting point of MgO (3125K) higher than the melting point of NaCl (1074K)? |
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Definition
The +2 and -2 ions attract each other more strongly than +1 attracts -1.
The ions Mg+2 and O-2 are smaller than Na+1 and Cl-1, therefore the ions can get closer together, increasing their electrostatic attractions.
Greater electrostatic attractions make it harder to melt. |
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Term
Molecular Compound Interactions
[image]
Polar Covalent compounds align according to dipole-dipole interactions.
Non-Polar Covalent compounds align according to LDF’s as a solid.
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Definition
Which of the following are broken when water boils?
A. Covalent bonds
B. Hydrogen bonds
C. Dipole-dipole interactions
D. London Dispersion Forces
(All of the IMF forces are broken--that's what boiling does. It's still the same molecule.)
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