unit 3 hws
What is the expected bond order for the diatomic species B2?
1
Which of the following statements concerning molecular orbital theory is true? 1. Bonding orbitals are lower in energy than their corresponding anti-bonding orbitals. 2. If a molecule has an odd number of electrons, then it is paramagnetic. 3. The MO diagrams for O2, F2, Ne2 are NOT filled using the Aufbau principle.
1 and 2
Which of the following molecules are likely to form hydrogen bonds? 1. CH3CH2OH 2. CH3COOH 3. CH3CHO 4. CH3OCH3
1 and 2 only
What type of intermolecular forces would you expect to find in a pure liquid sample of carbon tetrachloride?
london
A sigma bond...
may exist alone or in conjunction with a pi bond.
A liquid with a high vapor pressure is called...
volatile.
Diamond and graphite are two crystalline forms of carbon. In which form are the C atoms arranged in flat sheets with one C bonded to three nearby C atoms?
graphite
The vapor pressure of all liquids...
increases with temperature.
Forces between particles (atoms, molecules, or ions) of a substance are called...
intermolecular forces.
Which of the following interactions is generally the strongest?
ionic interactions
Will H2+ be more or less stable than H2 and why?
less stable; H2+ has one less electron in bonding orbitals
Which of the following statements regarding intermolecular forces (IMF) is/are true? 1. IMF result from attractive forces between regions of positive and negative charge density in neighboring molecules. 2. The stronger the bonds within a molecule are, the stronger the intermolecular forces will be. 3. Only non-polar molecules have instantaneous dipoles.
1 only
Draw the Lewis structure for NO2-. How many single bonds, double bonds, triple bonds, and unshared pairs of electrons are on the central atom, in that order, when considering a single contributing structure (ignoring the averaging effects of resonance)? Correct!
1, 1, 0, 1
Which of the following are important contributions that MO theory makes to chemistry? 1. The ability to use MO theory with a computer to calculate the minimum energy geometry of a molecule. 2. The ability to predict the energy at which a molecule will absorb light. 3. The ability to predict whether or not a molecule should be paramagnetic or diamagnetic.
1, 2, and 3
Consider a 3-atom molecule A-B-A for which B has a total of only four valence electrons - enough to make two bonds. Predict the A-B-A bond angle.
180°
Which of the following statements concerning molecular orbital theory is/are true? 1. Bonding orbitals are equal in energy to their corresponding anti-bonding orbitals. 2. Adding electrons to anti-bonding orbitals destabilizes molecules. 3. Unlike when we fill atomic orbitals, we DON'T use Hund's Rule to fill molecular orbitals.
2 only
Based on the general concepts that govern intermolecular attractions, which of the following orderings of fluorocarbons is correct when going from highest to lowest boiling point? 1. CF4 2. F3C-(CF2)4-CF3 3. F3C-(CF2)2-CF3
2, 3, 1
The sp3 hybridization has what percent s character and what percent p character respectively?
25%, 75%
Which of the following must be observed when filling a molecular orbital energy diagram?
Aufbau Principle, Hund's Rule, and Pauli Exclusion Principle
Which pair of bonded atoms has the largest dipole moment?
C-F
Which would you expect to have the highest vapor pressure at a given temperature?
C2H6
Which would you expect to be the most viscous?
C8H18 at 30°C
Which of the following statements about polarity is FALSE?
CCl4 is a polar molecule.
Which of the following would you expect to boil at the lowest temperature?
CH4
Which of the following, in the solid state, would be an example of a molecular crystal?
CO2
Which of the following structures represents a possible hydrogen bond?
F-H ······ F
Put the following compounds in order of increasing melting points. LiF, HF, F2, NF3
F2, NF3, HF, LiF
In the molecule, C2H4, what are the atomic orbitals that participate in forming the sigma bond between the C and H atoms?
H: 1s, C: sp2
Which of the following is not correctly paired with its dominant type of intermolecular forces?
HBr, hydrogen bonding
Which of the following molecules has the largest dipole moment?
HCl
According to molecular orbital theory, which of the following is NOT predicted to exist?
He2
Why is I2 a solid while H2 is a gas?
I2 is more polarizable than H2.
Which of KBr or CH3Br is likely to have the higher normal boiling point?
KBr
Identify the kinds of intermolecular forces that might arise between molecules of N2H4.
London forces, dipole-dipole, and hydrogen bonding
Which of the following species possesses a delocalized bond?
NO3-
Rank the following in order of increasing vapor pressure at a fixed temperature: H2O, CH3Cl, He, NaCl
NaCl < H2O < CH3Cl < He
Which of the following has bond angles of 90°, 120°, and 180°?
SF4
Which of the following solids is a covalent network?
SiO2(s)
A chemist has synthesized two new dyes based on the molecular structure of plant-based dyes. The lowest energy absorption line for the first dye is light in the visible region at 530 nm. The lowest energy absorption line for the second dye is light in the visible region at 645 nm. Based on this evidence, which molecule has the larger HOMO-LUMO gap?
The dye that absorbs at 530 nm.
Which of the following statements is true about a molecule with a bond order of one?
The molecule has a single bond
Tetrabromomethane has a higher boiling point than tetrachloromethane.
True
Is IF4- non-polar?
Yes, it is non-polar.
A central atom is surrounded by four chlorine atoms. Which of the following combinations is possible?
a trigonal bipyramidal electronic geometry and seesaw molecular geometry
The electronegativity of H is...
about equal to that of C.
Which of the following statements IS correct? Dispersion forces...
are also called London forces. are the only forces between nonpolar molecules. are temporary rather than permanent dipole-dipole interactions.
Determine the molecular geometry of the ion NO2-.
bent or angular
Which of the following molecules is nonpolar? Correct!
bf3
In a new compound, it is found that the central carbon atom is sp2 hybridized. This implies that...
carbon is also involved in a pi bond.
Which of the following statements is NOT correct? Dispersion forces...
decrease in strength with increasing molecular size.
Which of the following, in the solid state, would be an example of a covalent crystal?
diamond
What would be the most significant type of intermolecular forces in a liquid sample of fluoroform (CHF3)?
dipole-dipole
Very weak and very short range attractive forces between temporary (induced) dipoles are called...
dispersion forces
What is the predominant intermolecular force between IBr molecules in liquid IBr?
dispersion forces
The dominant forces between molecules are...
electromagnetic.
N2 has a bond order of 3 and O2 has a bond order of 2. Based on this information, choose the response that best completes the following sentence: N2 is (less, more) stable than O2, and has a (larger, shorter) bond length and a (higher, lower) bond energy.
more, shorter, higher
CHF3 is (less, more) polar than CHI3 because...
more, the C-F bonds are more polar than the C-I bonds.
Which of the following has bond angles slightly LESS than 120°?
o3
What is the electronic geometry of IF4-?
octahedral
Consider the molecule B2 (explored above in question #4). What is the magnetism and number of unpaired electrons in B2?
paramagnetic, 2
Predict which of butane (C4H10) or propanone (CH3COCH3) has the greater viscosity. Assume that they are both at the same temperature and in their liquid form.
propanone
Which of the following is a polar molecule?
sf4
Which of the following, in the solid state, would be an example of an ionic crystal?
sodium nitrate
What hybridization would you expect for C in ethyne (C2H2)?
sp
What hybridization would you expect for Se when it is found in SeO42-? Correct!
sp3
Which of the following combinations of hybridization and molecular geometry is possible?
sp3, trigonal pyramidal
What is the molecular geometry of IF4-?
square planar
A drop of liquid tends to have a spherical shape due to the property of...
surface tension.
Metallic solids are solids composed of metal atoms that are held together by metallic bonds. They also tend to be good conductors because...
the electrons in metallic solids are delocalized.
Surface tension describes...
the inward forces that must be overcome in order to expand the surface area of a liquid.
An antibonding orbital is formed when...
the overlap of the corresponding atomic orbitals leads to destructive interference.
What is the geometry around the left-most carbon in the molecule CH2CHCH3?
trigonal planar
What is the shape (molecular geometry) of COCl2?
trigonal planar
sp2 hybrid orbitals have...
trigonal planar symmetry.
