Q: Which equation would you use to relate the density of a crystal to its unit cell parameters?

$$\text{density} = \frac{\text{mass}}{\text{volume}}$$

Question 1

Which of the following best describes the bonding in network covalent solids such as diamond?

Accepted Answer

Atoms are held together by a continuous network of covalent bonds.

Question 2

Which property is most characteristic of metallic solids?

Accepted Answer

They are malleable and ductile due to delocalized electrons.

Question 3

Which equation is used to determine the distance between planes in a crystal using X-ray diffraction?

Accepted Answer

$$n \lambda = 2d \sin 	heta$$

Question 4

Given the ionic radii of $$	ext{Na}^+ (99 pm) $$and $$	ext{Cl}^- (181 pm$$), what is the edge length of the unit cell in NaCl?

Accepted Answer

$$560 	ext{ pm}$$

Question 5

Which type of crystalline solid is most likely to have the highest melting point?

Accepted Answer

Network covalent solids

Question 6

Which of the following best explains why MgO has a higher melting point than NaCl?

Accepted Answer

MgO has ions with higher charges, leading to stronger electrostatic attractions.

Question 7

In a face-centered cubic (fcc) unit cell, how many atoms are effectively contained within one unit cell?

Accepted Answer

4

Question 8

Which of the following is a real-world application of X-ray diffraction?

Accepted Answer

Determining the atomic arrangement in a crystal

Question 9

Which equation would you use to relate the density of a crystal to its unit cell parameters?

Accepted Answer

$$	ext{density} = \frac{	ext{mass}}{	ext{volume}}$$

Question 10

Which type of hole in a closest-packed structure is occupied by cations in the NaCl crystal structure?

Accepted Answer

Octahedral holes

Question 11

Which of the following best describes the structure of graphite?

Accepted Answer

Layers of atoms held together by dispersion forces

Question 12

Which factor most strongly affects the lattice energy of an ionic solid?

Accepted Answer

The charge and size of the ions

Question 13

Which of the following is true for the coordination number in a face-centered cubic (fcc) lattice?

Accepted Answer

The coordination number is 12.

Question 14

Which type of solid is most likely to be soluble in water and conduct electricity when dissolved?

Accepted Answer

Ionic solid

Question 15

Which of the following statements about the CsCl crystal structure is correct?

Accepted Answer

Cs+ ions occupy cubic holes in a simple cubic lattice of Cl- ions.

Question 16

Which of the following best explains why diamond is an excellent electrical insulator?

Accepted Answer

Diamond has a three-dimensional network of covalent bonds with no free electrons.

Question 17

A crystal has a unit cell edge length of $$287 	ext{ pm}$$ and contains two atoms per unit cell. If the molar mass is $$55.85 	ext{ g/mol}$$, what is the density of the crystal?

Accepted Answer

$$7.86 	ext{ g/cm}^3$$

Question 18

Which of the following is a key difference between ionic and molecular solids?

Accepted Answer

Ionic solids conduct electricity when dissolved in water, while molecular solids do not.

Question 19

Which of the following best describes the relationship between lattice energy and the enthalpy of formation for an ionic compound?

Accepted Answer

Lattice energy is one of several energy terms used to calculate the enthalpy of formation.

Question 20

Which of the following would you expect to have the greater solubility in water: NaCl or MgCl2? Explain.

Accepted Answer

NaCl, because it has a lower lattice energy and smaller ions.

Network Covalent and Ionic Solids: Crystal Structures and Energy Changes

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