# Bonding and Structure

7. (Unit cells; Ch. 3 "Companion") A corner atom is part of how many unit cells?
.

1, 2, 4, 8

At-Seat Demonstration: cubes like dice can be handed out for students to examine for this question.

8. (Coordination number; Ch. 5 "Companion") In the two-dimensional square packing shown, what is the coordination number of the central atom?

2, 4, 6

9. (Coordination number; Ch. 5 "Companion") At-Seat Demonstration: Give students 10 pennies (students can share a set of ten) and ask them to pack them at their desks to determine the largest coordination number in two dimensions.

4, 6, 8, 9

25. (Lewis dot structures, octet rule) What is a correct Lewis dot representation of carbon monoxide?

26. (Lewis dot structures, bonding) Compare O-O and O=O. Is O=O expected to be

stronger, weaker, or the same strength?

Is O=O expected to be

longer, shorter, or the same length?

27. (VSEPR) Demonstration 5.3 "Companion": Provide students with small plastic tetrahedral and octahedral models to share during VSEPR lectures. With four electron pairs, can the pairs be equally spaced and farther apart than the 90° of a square arrangement?

yes, no

Determine the Lewis dot structure of NH3 and use the models to determine its molecular geometry.

linear, bent, pyramidal

Repeat for H2O.

linear, bent, pyramidal

A tetrahedron can be inscribed inside a cube, represented in the layer sequence formalism shown below. If sphere 1 is part of the tetrahedron, which other three spheres are as well?

2, 3, 4
3, 5, 7
3, 6, 8

An octahedron can be inscribed inside a cube. If spheres 1 and 6 (below) are part of the octahedron, where do the other four spheres go?

z = 1/4, 1/2, 3/4

What is their arrangement?

A, B, C

28. (VSEPR) At-Seat Demonstration (use models described above): The center of a tetrahedron resting on three bonds

is midway from top to bottom, is closer to the bottom, is closer to the top

The center of a tetrahedron balanced on two bonds

is midway from top to bottom, is closer to the bottom, is closer to the top

The center of an octahedron resting on three bonds

is midway from top to bottom, is closer to the bottom, is closer to the top

The center of an octahedron balanced on one bond

is midway from top to bottom, is closer to the bottom, is closer to the top

This can be connected to location of centers of octahedral and tetrahedral holes in close-packing arrangements of atoms/ions.

29. (Close packed spheres, holes; Ch. 5 "Companion") The figure below is a ZnS (zinc blende) layer sequence. The atom indicated by an arrow sits in one of the tetrahedral holes of the structure. Which atoms form this hole?

1,4,7,8
1,3,4,7
1,3,6,7

30. (Close packed spheres, holes; Ch. 5 "Companion") In the zinc blende layer sequence below, what fraction of the tetrahedral holes are filled?

1/8, 1/4, 1/2, all

31. (Close packed spheres, holes; Ch. 5 "Companion") C60 (buckyball) is cubic closest packed (face-centered cubic) in its crystalline form. If you insert potassium atoms into all the tetrahedral and octahedral holes of the C60 structure, the formula would become KxC60 . What is the value of x?

1, 2, 3, other

32. (Polarity; dipole moments) Demonstration: Beakers of water, carbon tetrachloride, and dry ice (carbon dioxide) are to be placed into a microwave oven. Based on dipole moment, which are predicted to be heated by the microwave radiation (measure temperature with digital thermometer before and after)?

water, carbon tetrachloride, carbon dioxide

33. (Bands; Ch. 7 "Companion") The 3s band of solid Na will have as many orbitals (each delocalized over the entire solid) as the number of 3s orbitals from Na atoms in the sample. If each orbital of the band can hold two, spin-paired 3s valence electrons, to what extent will the band be filled?

completely empty, half filled, completely filled

To what extent will the Na 2s band be filled?

completely empty, half filled, completely filled

Which is the best electronic band population for good electrical conductivity (metallic behavior), if a net flow of electrons through a band is needed? Demonstration 7.1 "Companion": A requirement for electrical conductivity is net electron flow in a particular direction in a sample. At what capacity should the band be filled with electrons to best promote electrical conductivity? Have three jars sealed tightly: one empty (represents empty band), one partially-filled (represents partially filled band) and one completely filled (represents filled band). If the filler (sand or packing peanuts, e.g.) represents electrons and tipping the jar represents the application of a voltage, which jar(s) will exhibit net motion of the filler?

empty, partially filled, filled

In which part of the filled portion of the band is net motion greatest?

top, middle, bottom

35. (Bands; Ch. 7 "Companion") Which of these band diagrams is consistent with diamond being an electrical insulator?

A, B, C

Another approach is to have students determine which bands are filled to which extent, and then decide if each band scenario in turn (A, B, then C) corresponds correctly to diamond's being an electrical insulator rather than a conductor (metal). The s, p combination band can be related to sp3 hybrid orbitals if desired.

36. (Semiconductors; Ch. 7 "Companion") When an electron falls back into a bond (localized picture) or valence band (delocalized picture), what change in energy occurs?

energy is released, energy is absorbed, no change in energy occurs

38. (Band gap energy, spectroscopy, semiconductors; Ch. 7 "Companion") Setup: Band gap energy has been introduced in a localized picture: it can be defined as the energy needed to remove an electron from a bond in the solid, enabling the electron to move freely through the solid to conduct electricity. When itinerant electrons return to such a one-electron bond, the band gap energy can be released as a photon. The band gap energy is to a first approximation expected to increase as the bonds become stronger and shorter and the electrons are held more tightly. The group 14 elements illustrate this effect with diamond being an electrical insulator, silicon and germanium (longer, weaker bonds in the same diamond structure) being semiconductors, and tin being a metal. Demonstration 7.11 "Companion": A trio of related predictions: what will happen to interatomic spacing, band gap energy, and the color of the light emitted when an orange LED is cooled in liquid nitrogen. On cooling,

atoms will get closer together, atoms will get farther apart
band gap energy increases, band gap energy decreases
color of light will become more red, color of light will become more yellow

42. (Elemental analysis, diffraction, solid solutions; Ch. 3 & 4 "Companion") Sample A is an equimolar physical mixture of Si and Ge. Sample B is a Si0.5Ge0.5 solid solution. Which measurements will be identical and which different for the two samples?

elemental analysis: same, different
x-ray diffraction: same, different
absorption spectrum: same, different

50. (Layer sequences; Ch. 3 & 5 "Companion") How many atoms are in the following layer sequence of the diamond structure?

4, 6, 8, 13

What is the coordination number?

4, 6, 8

What is the coordination geometry?

tetrahedral, square, octahedral, cubic

54. (Diffraction, optical transforms; Ch. 4 "Companion," Demonstration 4.1) The equation dx = lL defines the relationship between incident wavelength l, spacing of repeating features d, spacing between diffracted spots x, and distance between transform slide and screen L. Consider which variables are directly and inversely related to predict the following.

When the wavelength is decreased from red to green (demonstration with 633 and 543 nm HeNe lasers), should the spacing between diffraction spots

increase, decrease, stay the same

(This relationship can also be seen by having students view a point source of white light through their personal transform slide, as described in Demonstration 4.1, and having them note which part of the full spectrum they observe for each diffracted spot, violet or red, is giving rise to the largest spacing).

When the distance between slide and screen is increased, the spacing between diffraction spots should

increase, decrease, stay the same

When the spacing between features on the transform slide increases, the spacing between diffraction spots should

increase, decrease, stay the same

65. (Unit cells, layer sequences, close packed spheres; Ch. 3 & 5 "Companion") A layer sequence for an FCC = CCP metal is shown below.

A face diagonal passes through the center of atom 4 and the center(s) of which other atom(s)?

1, 2, 5, 11 Also correct: 8, 12 & 9, 10

A body diagonal passes through the center of atom 4 and the center(s) of which other atom(s)?

2, 5, 11, 14

A close-packed plane is comprised of six atoms. If atoms 2, 4, 5 are three of the six atoms, which other three atoms are need to define the plane?

11, 13, 14; 6, 9, 13; 7, 8, 12; 6, 9, 10

71. (Organic chemistry) In the shorthand for organic molecules, octane is written as follows:

How many hydrogen atoms are present in this molecule?

16, 18, 20

How many hydrogen atoms are present in ethene, ?

2, 4, 6, 8

73. (Chirality) Do enantiomers have the same density?

yes, no

melting point?

yes, no

If acids, the same pKa?

yes, no

74. (Chirality) How many stereogenic carbon atoms are present in the glucose molecule pictured below?

3, 4, 5, 6

76. (Polymers) Some polymerization reaction conditions lead largely to linear chains of polyethylene, A, and other conditions cause considerable branching, B. Which structure corresponds to high density polyethylene (HDPE)?

A, B

86. (Semiconductors, bands; Ch.8 "Companion") Pictured below is an energy band diagram for silicon.

When doped into Si, Al is a(n)

donor, acceptor

When doped into Si, P is a(n)

donor, acceptor

Which energy level corresponds to Al?

A, B

Which energy level corresponds to P?

A, B

87. (Semiconductors, doping; Ch 8 "Companion") Which is a weaker acceptor (analogous to weaker acid)

In, Cu

Which is a weaker donor (analogous to weaker base)?

As, Mn

92. (Close packed spheres, holes) Demonstration: If four identical spheres are placed in contact to form a tetrahedral hole, can an identical sphere fit into the hole?

yes, no

93. (Close packed spheres, holes) Demonstration: Which is a smaller hole?

One formed by a tetrahedron of identical spheres, one formed by an octahedron of identical spheres

A sphere that fits snugly into an octahedron can be shown not to fit into a tetrahedral hole.

94. (Bonding) Demonstration: Obtain samples of copper and silicon. Hit each with a hammer. Which would be predicted to have directional covalent bonds?

Cu, Si

97. (Chelation) What is the maximum number of ethylenediamine bidentate ligands that can bond to Ni to form an octahedral complex?

2, 3, 6

104. (Organic chemistry, bonding, Lewis dot structure) To complete the Lewis dot structure of benzene, how many double bonds must be added?

1, 2, 3, 6

112. (Density, close packed spheres) Demonstration: Which is denser?

Stacking a second close-packed layer of spheres directly atop a close-packed layer below, Stacking a second close-packed layer of spheres in the depressions formed by spheres in the close-packed layer below.

114. (Plastic deformation, slip planes; Ch. 6 "Companion") Which situation allows easiest slippage of planes of atoms past one another, as sketched below?

identical spheres in both layers, a layer with a large impurity atom, a layer with a small impurity atom

Which of the two impurities acts like a "speed bump" and which like a "pothole," in impeding movement along slip planes? (see figure above)

115. (Electronegativity, bonding, band gap energy; Ch. 7 "Companion") The atoms below have the following electronegativities:

The three isoelectronic semiconductors Ge, GaAs, and ZnSe all have roughly the same size unit cell and internuclear separation (exclusively Ge-Ge, Ga-As, and Zn-Se bonds, respectively). If under these conditions, band gap energy increases with ionic character, which isoelectronic solid should have the largest band gap energy?

Ge, GaAs, ZnSe

117. (Chelation, coordination chemistry, chirality) At-Seat Demonstration: Pass out three small rubber bands with the plastic octahedra (see problem 27). Instruct students to share two octahedra and six rubber bands. Have them make mirror image tris chelate complexes, using the rubber band as a chelating ligand. Are these superimposable?

yes, no

118. (Tetrahedron, chirality) At-Seat Demonstration: Four colors of circular paper stickers (green, yellow, pink, and orange, e.g.) can be obtained on long sheets. Instruct students to share two tetrahedra and two stickers of each of the four colors. Have them make mirror image tetrahedra with a different color on each leg (representing four different substituents). Are these superimposable?

yes, no

Repeat using two different colors (two substituents identical). Are these superimposable?

yes, no

More questions are needed for this section. Please submit contributions to concept@chem.wisc.edu..