Unit 3 Hws

25 July 2022
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question
The electronegativity of H is...
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about equal to that of C.
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Which pair of bonded atoms has the largest dipole moment?
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C-F
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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.
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180掳
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What is the shape (molecular geometry) of COCl2?
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trigonal planar
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Which of the following has bond angles slightly LESS than 120掳?
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o3
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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!
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1, 1, 0, 1
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Determine the molecular geometry of the ion NO2-.
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bent or angular
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What is the electronic geometry of IF4-?
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octahedral
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What is the molecular geometry of IF4-?
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square planar
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Is IF4- non-polar?
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Yes, it is non-polar.
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What is the geometry around the left-most carbon in the molecule CH2CHCH3?
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trigonal planar
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Which of the following has bond angles of 90掳, 120掳, and 180掳?
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SF4
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A central atom is surrounded by four chlorine atoms. Which of the following combinations is possible?
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a trigonal bipyramidal electronic geometry and seesaw molecular geometry
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Which of the following is a polar molecule?
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sf4
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Which of the following statements about polarity is FALSE?
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CCl4 is a polar molecule.
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Which of the following molecules is nonpolar? Correct!
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bf3
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CHF3 is (less, more) polar than CHI3 because...
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more, the C-F bonds are more polar than the C-I bonds.
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Which of the following molecules has the largest dipole moment?
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HCl
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Which of the following combinations of hybridization and molecular geometry is possible?
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sp3, trigonal pyramidal
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The sp3 hybridization has what percent s character and what percent p character respectively?
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25%, 75%
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What hybridization would you expect for Se when it is found in SeO42-? Correct!
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sp3
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What hybridization would you expect for C in ethyne (C2H2)?
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sp
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sp2 hybrid orbitals have...
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trigonal planar symmetry.
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A sigma bond...
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may exist alone or in conjunction with a pi bond.
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In a new compound, it is found that the central carbon atom is sp2 hybridized. This implies that...
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carbon is also involved in a pi bond.
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In the molecule, C2H4, what are the atomic orbitals that participate in forming the sigma bond between the C and H atoms?
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H: 1s, C: sp2
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What is the expected bond order for the diatomic species B2?
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1
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Consider the molecule B2 (explored above in question #4). What is the magnetism and number of unpaired electrons in B2?
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paramagnetic, 2
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According to molecular orbital theory, which of the following is NOT predicted to exist?
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He2
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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.
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more, shorter, higher
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Which of the following species possesses a delocalized bond?
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NO3-
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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.
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1 and 2
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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.
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2 only
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Which of the following statements is true about a molecule with a bond order of one?
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The molecule has a single bond
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Which of the following must be observed when filling a molecular orbital energy diagram?
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Aufbau Principle, Hund's Rule, and Pauli Exclusion Principle
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Will H2+ be more or less stable than H2 and why?
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less stable; H2+ has one less electron in bonding orbitals
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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?
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The dye that absorbs at 530 nm.
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An antibonding orbital is formed when...
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the overlap of the corresponding atomic orbitals leads to destructive interference.
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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.
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1, 2, and 3
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Forces between particles (atoms, molecules, or ions) of a substance are called...
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intermolecular forces.
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What would be the most significant type of intermolecular forces in a liquid sample of fluoroform (CHF3)?
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dipole-dipole
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What is the predominant intermolecular force between IBr molecules in liquid IBr?
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dispersion forces
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Which of the following structures represents a possible hydrogen bond?
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F-H 路路路路路路 F
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Identify the kinds of intermolecular forces that might arise between molecules of N2H4.
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London forces, dipole-dipole, and hydrogen bonding
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The dominant forces between molecules are...
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electromagnetic.
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Which of the following molecules are likely to form hydrogen bonds? 1. CH3CH2OH 2. CH3COOH 3. CH3CHO 4. CH3OCH3
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1 and 2 only
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Which of the following is not correctly paired with its dominant type of intermolecular forces?
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HBr, hydrogen bonding
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Which of the following interactions is generally the strongest?
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ionic interactions
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Which of the following statements is NOT correct? Dispersion forces...
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decrease in strength with increasing molecular size.
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Which of the following statements IS correct? Dispersion forces...
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are also called London forces. are the only forces between nonpolar molecules. are temporary rather than permanent dipole-dipole interactions.
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Why is I2 a solid while H2 is a gas?
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I2 is more polarizable than H2.
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Very weak and very short range attractive forces between temporary (induced) dipoles are called...
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dispersion forces
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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.
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1 only
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Put the following compounds in order of increasing melting points. LiF, HF, F2, NF3
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F2, NF3, HF, LiF
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What type of intermolecular forces would you expect to find in a pure liquid sample of carbon tetrachloride?
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london
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A drop of liquid tends to have a spherical shape due to the property of...
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surface tension.
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Surface tension describes...
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the inward forces that must be overcome in order to expand the surface area of a liquid.
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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.
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propanone
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Which would you expect to be the most viscous?
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C8H18 at 30掳C
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The vapor pressure of all liquids...
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increases with temperature.
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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
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2, 3, 1
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Tetrabromomethane has a higher boiling point than tetrachloromethane.
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True
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Which of KBr or CH3Br is likely to have the higher normal boiling point?
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KBr
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Which of the following would you expect to boil at the lowest temperature?
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CH4
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A liquid with a high vapor pressure is called...
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volatile.
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Which would you expect to have the highest vapor pressure at a given temperature?
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C2H6
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Rank the following in order of increasing vapor pressure at a fixed temperature: H2O, CH3Cl, He, NaCl
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NaCl < H2O < CH3Cl < He
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Which of the following solids is a covalent network?
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SiO2(s)
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Which of the following, in the solid state, would be an example of a covalent crystal?
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diamond
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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?
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graphite
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Which of the following, in the solid state, would be an example of a molecular crystal?
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CO2
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Which of the following, in the solid state, would be an example of an ionic crystal?
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sodium nitrate
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Metallic solids are solids composed of metal atoms that are held together by metallic bonds. They also tend to be good conductors because...
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the electrons in metallic solids are delocalized.