Ch10 Chem Concepts

Question 1

What can crystalline solids be categorized by?

Answer 1

ionic solids, molecular solids, covalent network solids, or metallic solids.

Question 2

describe ionic solids

Answer 2

• constituent particles are ions like NaCl
• alternating cations and anions
• held together by ionic bonds (ion-ion forces)
• brittle, hard, high-melting

Question 3

molecular solids

Answer 3

• are like sucrose or ice
• held together by intermolecular forces (dispersion forces, dipole-dipole forces, hydrogen bonds)
• soft, low-melting, nonconducting

Question 4

covalent network solids

Answer 4

• like diamond or quartz
• atoms are linked together by covalent bonds into a giant 3D array.
• in effect, a covalent network solid is one very large molecule
• hard, high melting

Question 5

metallic solids

Answer 5

• like silver, iron
• consists of large arrays of atoms
• their crystals have metallic properties such as electrical conductivity
• metallic bonds
• variable hardiness and melting point, conducting

Question 6

simple cubic packing

Answer 6

all atoms are lined up in stacks and rows on top of one another
52% packing efficiency

Question 7

body-centered cubic packing

Answer 7

a-b-a-b arrangement, the spheres in the b layer fit into the depressions of the spheres in the “a” layer
68% packing efficiency

Question 8

hexagonal closest-packed

Answer 8

a-b-a-b arrangement. each layer has a hexagonal arrangement of touching spheres, which are offset so that spheres in a “b” layer fit into the small triangular depressions between spheres in an “a” layer
74% packing efficiency

Question 9

cubic closest-packed

Answer 9

a-b-c arrangement . Three alternating layers. First 2 layers are the same as the hexagonal, but the third layer does not cover the middle offset if that makes sense.
74% packing efficiency

Question 10

primitive cubic unit cell

Answer 10

8 1/8ths of an atom; therefore 1 atom in per unit cell

-repeat unit found in simple cubic packing

Question 11

body-centered cubic unit cell

Answer 11

8 1/8ths of an atom, plus 1 full atom at the center.
therefore 2 atom per unit cell
-repeat unit found in body-cubic packing

Question 12

face-centered cubic unit cell

Answer 12

8 1/8ths of an atom, plus 6 1/2s of an atom, therefore 4 atoms per unit cell
-repeat unit found in cubic closest packed.