Chem prep and in class problems exam #3

Why does a molecule adopt a square planar molecular shape if a molecule has 6 regions of electron density and two lone pairs? Select all statements that are true. (chp 11.B) - The total electron-electron repulsion is minimized by placing lone pairs in the equatorial positions. - An angle of 180º between lone pairs places them as far away from each other as possible. - The higher repulsion between bonding domains compared to between lone pairs forces the lone pairs to the axial positions. - The bonding domains adopt bond angles of 90˚ to minimize the electron-electron repulsion amongst themselves.

- An angle of 180º between lone pairs places them as far away from each other as possible. - The bonding domains adopt bond angles of 90˚ to minimize the electron-electron repulsion amongst themselves.

Which statements are true regarding the radii of ions? (chp 9.A) - Anions are larger than their parent atoms because removal of an electron increases repulsion in the valence shell. - Cations are larger than their parent atoms because removal of an electron decreases repulsion in the valence shell. - Anions are larger than their parent atoms because addition of an electron increases repulsion in the valence shell. - Cations are smaller than their parent atoms

- Anions are larger than their parent atoms because addition of an electron increases repulsion in the valence shell. - Cations are smaller than their parent atoms because removal of an electron decreases repulsion in the valence shell.

Which molecule has the largest F-X-F bond angle, where X is the central atom? (chp 11.B) - BF3 - CF4 - OF2

- BF3

Which statement concerning bond enthalpy (bond dissociation energy) is true? (chp 10.C) - Bond enthalpy corresponds to the energy required for heterolytic cleavage of a bond toward the more electronegative atom in the bond. - Using bond enthalpies to determine reaction enthalpy is equivalent to using enthalpies of formation. - Greater bond enthalpy is associated with a weaker bond. - Greater bond enthalpy is associated with a longer bond. - Exact bond enthalpies can be measured only for diatomic molecules.

- Exact bond enthalpies can be measured only for diatomic molecules.

Which steps involved in the formation of a crystal lattice are exothermic? Select all that apply. (chp 9.B) - Breaking the bond of a diatomic molecule - Phase change of a solid phase atom to a gas phase atom. - Formation of an anion from a gas phase atom. - Attraction of a cation to an anion. - Formation of a cation from a gas phase atom

- Formation of an anion from a gas phase atom. - Attraction of a cation to an anion.

Which of the following element(s) can have expanded octets? Select all that apply. (chp 10.A) - Be - S - Xe - P - B - C - Se

- S - Xe - P - Se

Which statement best explains why the electron affinity of C is more negative (more exothermic) than that of N? (chp 9.B) - The addition of an electron to N results in a more stable electron configuration. The addition of an electron to C results in a less stable electron configuration. - C has fewer valence electrons than N. - N has more protons than C. - It takes more energy to remove an electron from a half-full subshell. - The addition of an electron to C results in a amore stable electron configuration. The addition of an electron to N results in a less stable electron configuration.

- The addition of an electron to C results in a amore stable electron configuration. The addition of an electron to N results in a less stable electron configuration.

Which statement is true regarding electron affinity? (chp 9.B) - The electron affinity for fluorine (F) is much more negative than that of nitrogen (N), indicating that the gain of one electron by a gas phase atom is more energetically favorable for F than for N. - The electron affinity of phosphorus (P) is more negative than that of silicon (Si) because phosphorus is less likely to lose an electron due to its stable electron configuration. - The electron affinity for oxygen (O) is less negative than that of nitrogen (N) because the stable electron configuration of N makes it less energetically favorable for it to gain an electron. - The electron affinities of Group 17 (7A) elements are close to 0 because it takes little energy to add electrons to gas phase atoms of these elements.

- The electron affinity for fluorine (F) is much more negative than that of nitrogen (N), indicating that the gain of one electron by a gas phase atom is more energetically favorable for F than for N.

Which statements are true regarding resonance? Select all that apply. (chp 10.B) - The "true" structure for a molecule that exhibits resonance is a blend of all of the possible resonance structures that can be drawn for the molecule. - The greatest contributor to the resonance hybrid may have several equivalent resonance structures. - If there are two possible locations in a molecule for a double bond, then two of the electrons in that bond switch back and forth between the two locations. - If there are inequivalent resonance structures for a given molecule, then the one that is the greatest contributor to the resonance hybrid is the lowest energy structure. - All of the possible resonance structures for a given molecule that can be drawn exist in nature.

- The greatest contributor to the resonance hybrid may have several equivalent resonance structures. - If there are inequivalent resonance structures for a given molecule, then the one that is the greatest contributor to the resonance hybrid is the lowest energy structure.

Which molecules have octahedral electron geometry? Select all that apply. (chp 11.B) - CCl4 - XeF4 - PCl5 - ClF5 - SCl6

- XeF4 - ClF5 - SCl6

Atom A has a smaller atomic radius than atom B. Which statement best explains why this is true? (chp 9.A) - Zeff for A is a greater percentage of its atomic number than is Zeff for B relative to its atomic number. - Atom A has fewer protons than atom B. - Atom A has more core electrons than B. - Atom B has more valence electrons than A. - The valence electrons of atom B are more strongly attracted to its nucleus than are the valence electrons of atom A to its nucleus.

- Zeff for A is a greater percentage of its atomic number than is Zeff for B relative to its atomic number.

The chemical formula of propane is C3H8. Which answer option forms the "backbone" of the Lewis structure for this molecule? (chp 10.A) -C-C-C- H-H-H-C-C-C-H-H-H H-C-H-C-H-C-H

-C-C-C-

What are the allowed values for the angular momentum quantum number when n = 4? Select all that apply. (chp 8.E) -4, -2, 1, 3, 2, 0, -1, -3, 4

1, 3, 2, 0

How many of the electrons in the ground state electron configuration for antimony (Sb) occupy s orbitals? (chp 8.D)

10

What is the maximum number of electrons that an atom may contain with n = 3? (chp 8.E)

18

Determine the number of radial nodes in the shape of a 3s orbital. (chp 8.E)

2

How many double bonds are there in the most significant resonance structure of the bromate ion (BrO3-)? (chp 10.B)

2

How many electrons in a given atom may have the combination of quantum numbers n = 5 and mℓ = -3? (chp 8.E)

2

How many unpaired electrons are in the ground state electron configuration for iron? (chp 8.D)

4

How many unpaired electrons are in the ground state electron configuration for Fe3+? (chp 8.D)

5

What is the total number of nodes for an f orbital with n = 6 and ℓ = 3? (chp 8.E)

5

Calculate the effective nuclear charge (Zeff) felt by the last electron of neon. (chp 9.A)

5.85

What is the highest-energy occupied orbital in the ground state electron configuration for antimony (Sb)? (chp 8.D)

5p

How many valence electrons does sulfur have? (chp 8.D)

6

How many 3d electrons are present in the ground-state electron configuration of Co2+? (chp 8.D)

7

How many valence electrons are in the Lewis structure for C6H12O6? (chp 10.A)

72

Calculate the shielding constant S for the last valence electron of aluminum (Al). (chp 9.A)

9.2

Arrange these ions in order of increasing ionic radius: Ca2+, Cl-, S2-, K+. (chp 9.A)

Ca2+ < K+ < Cl- < S2-

Draw the Lewis structure of ICl2-. (chp 10.B) For the quiz question, identify the central atom and the number of valence electrons in the Lewis structure.

Central atom: I Number of valence electrons: 22

Draw the Lewis structure for SiCl4. Identify the central atom and the number of valence electrons in the Lewis structure. (chp 10.A)

Central atom: S Number of valence electrons: 32

Identify the central atom and total number of valence electrons in the Lewis structure for sulfur hexafluoride. (chp 10.A)

Central atom: S Number of valence electrons: 48

Order the compounds from largest (1) to smallest (5) lattice energy. (chp 9.B) CsBr, SrO, CrN, MgO, Na2S

CrN > MgO > SrO > Na2S > CsBr

Match each chemical equation below with the type of energy involved. (chp 9.B) Equation 1. X(g) + e- → X-(g) + energy Equation 2. X(g) + energy → e- + X+(g)

Equation 1: electron affinity Equation 2: ionization energy

Select the smallest atom from the list below (try to answer without looking up actual atomic radii). (chp 9.A) K, Ca, Ge, F, Si

F

Rank the atoms in order of increasing electronegativity. (chp 10.A) C, N, F, O, H

F > O > N > C > H

Which of the following molecules would be expected to have bond angles that deviate significantly from the VSEPR ideal(s)? (chp 11.B) - Br3- - XeF4 - H3O+ - ICl4- - SF2

H3O+ SF2

Arrange these atoms in order of increasing atomic radius: N, O, Na, P. (chp 9.A)

O < N < P < Na

Rank the bonds below in order of increasing ionic character. (chp 10.C) S-F, S-O, N-Cl, O-Cl

S-F > S-O > O-Cl > N-Cl

Which of the following bonds has the smallest bond dipole? (chp 10.C) S-H Se-H Te-H O-H F-H

Te-H

Which statement is true regarding first ionization energy? (chp 9.B) - The first ionization energy for lithium should be greater than that for fluorine. - The first ionization energies for noble gases are very large as a result of their very stable electron configurations. - It represents the energy released when an electron is removed from a gas phase atom. - The first ionization energy for lithium should be less than that for sodium because sodium has fewer core electrons. - First ionization energy corresponds to the process: X(g) + e- → X-(g) + IE.

The first ionization energies for noble gases are very large as a result of their very stable electron configurations.

Which of the following orbitals is highest in energy for neutral atoms in the d block? (chp 8.D) a) 4d b) 3p c) 2s d) 4s e) 2p f) 1s

a) 4d

Which statements are true regarding nodes? Select all that apply. (chp 8.E) a) A 4s orbital has three radial nodes. b) Radial nodes are characteristic of the shape of an orbital. c) There is a near zero probability of finding an electron in a radial node. d) The number of radial nodes depends on both the energy level and the subshell. e) All orbitals in the n = 4 energy level have three radial nodes. f) The number of radial nodes depends only on the energy level of the orbital.

a) A 4s orbital has three radial nodes. c) There is a near zero probability of finding an electron in a radial node. d) The number of radial nodes depends on both the energy level and the subshell.

Which criteria are important in determining the Lewis structure for a molecule that is the greatest contributor to the resonance hybrid? Select all that apply. (chp 10.B) a) The structure has the most double bonds possible. b) The formal charges sum to the overall charge on the molecule or ion. c) The most electronegative atom has the most positive formal charge. d) The magnitude of the formal charges is maximized. The structure has no adjacent like charges.

b) The formal charges sum to the overall charge on the molecule or ion. e) The structure has no adjacent like charges.

Rank the bonds in order of decreasing number of electrons between the atoms involved. (chp 10.A) a) double bond > triple bond > single bond b) triple bond > double bond > single bond c) single bond > double bond > triple bond d) single bond > triple bond > double bond e) triple bond > single bond > double bond

b) triple bond > double bond > single bond

Fill in the blanks below. Note that bond enthalpies are positive by convention. (chp 10.C) The enthalpy change of a chemical reaction can be estimated as the bond enthalpies of all bonds ___________ ["made", "broken"] minus the enthalpies of all bonds ___________ ["broken", "made"] .

broken, made

The last electron placed in the ground-state electron configuration for germanium (Ge) is in what type of orbital? (chp 8.D) a) 3p b) 3s c) 4p d) 3d e) 4s

c) 4p

Three atoms have the following ground state electron configurations. Which statement regarding the atoms is true? (chp 10.A) Atom 1: 1s22s22p63s23p2 Atom 2: 1s22s22p63s23p5 Atom 3: 1s22s22p63s23p64s1 a) In a bond, atom 1 gets a larger share of an electron pair than atom 2. b) Atom 1 is the most electronegative atom. c) Atom 2 has the greatest ability to attract electrons to itself in a bond. d) Atom 3 attracts electrons more strongly than atom 1 in a bond.

c) Atom 2 has the greatest ability to attract electrons to itself in a bond.

Which statement is true regarding resonance? (chp 10.B) a) The conversion of one resonance form to another is a chemical change. b) In a molecule characterized by multiple resonance forms, a given pair of electrons oscillates back and forth between multiple locations. c) In a molecule that exhibits resonance, a given electron pair is distributed between two locations. d) All valid Lewis structures for a molecule contribute equally to the resonance hybrid. e) A molecule must have a double or triple bond to exhibit resonance.

c) In a molecule that exhibits resonance, a given electron pair is distributed between two locations.

Consider starting with a neutral atom in the gas phase. Which of the following best describes the first ionization energy? (chp 9.B) a) The energy required to form an anion. b) The energy released when an anion forms. c) The energy required to form a cation. d) The energy released when a cation forms.

c) The energy required to form a cation.

Which statement is true regarding effective nuclear charge, Zeff? (chp 9.A) a) Z < Zeff for any atom with more than one electron. b) Zeff is the number of protons in the nucleus of the atom. c) Z > Zeff for any atom with more than one electron.

c) Z > Zeff for any atom with more than one electron.

What information does the magnetic quantum number convey? Select all that apply. (chp 8.E) a) the energy of the orbital b) the shape of the orbital c) the orientation of the orbital relative to the x, y, and z axes d) the number of nodes the orbital has e) the size of the orbital

c) the orientation of the orbital relative to the x, y, and z axes

The formation of a crystal lattice of KF involves several steps, some of which are endothermic and some of which are exothermic. Which step releases the most energy? (chp 9.B) a) Formation of the potassium cation b) Breaking the F2 bond c) Conversion of solid potassium atoms to gaseous potassium atoms d) Attraction of the potassium cation to the fluoride anion e) Formation of the fluoride anion

d) Attraction of the potassium cation to the fluoride anion

Which compound do you expect to have the lattice energy with the greatest magnitude? (chp 9.B) a) CaCl2 b) FeCl3 c) NaCl d) KCl e) Fe2S3

e) Fe2S3

An atom or ion has the abbreviated electron configuration [Kr]. Select the species that it could not possibly be. (chp 8.D) a) Sr2+ b) Rb+ c) Se2- d) Br- e) K+

e) K+

f

f

Anomalies to periodic trends in first ionization energy occur around which groups on the periodic table? (chp 9.B) a) 1 and 18 b) 2 and 17 c) 18 only d) 1 and 15 e) 2 and 18 f) 13 and 16

f) 13 and 16

ga

fs

fg

g

Select the set of quantum numbers that describe the electron that is highest in energy. (chp 8.E) n = 1, l =0, ml = 0, ms = +1/2 n = 4, l =1, ml = 1, ms = -1/2 n = 1, l =0, ml = 0, ms = -1/2 n = 4, l =0, ml = 0, ms = +1/2 n = 3, l =2, ml = 1, ms = +1/2

n = 4, l =1, ml = 1, ms = -1/2

Determine the molecular shape (or molecular geometry) for each molecule below. (chp 11.B) boron trifluoride carbon tetrachloride oxygen difluoride xenon tetrafluoride

trigonal planar tetrahedral bent square planar

Consider the covalent bonds below. Indicate the positive and negative ends of the bond dipole in each case. (chp 10.C) S- Cl C-O

δ+, δ- δ+, δ-