Chapter 12

A solid is soft and has a low melting point (below \(100^{\circ} \mathrm{C}\) ). The solid, its melt, and a solution containing the substance are all nonconductors of electricity. Classify the solid.

A solid is very hard and has a high melting point. Neither the solid nor its melt conducts electricity. Classify the solid.

Why are metals good conductors of heat and electricity? Why does the ability of a metal to conduct electricity decrease with increasing temperature?

Classify the solid states of the elements in the second period of the periodic table.

Which of these are molecular solids and which are covalent solids: \(\mathrm{Se}_{8}, \mathrm{HBr}, \mathrm{Si}, \mathrm{CO}_{2}, \mathrm{C}, \mathrm{P}_{4} \mathrm{O}_{6}, \mathrm{~B},\) \(\mathrm{SiH}_{4} ?\)

What is the coordination number of each sphere in (a) a simple cubic lattice, (b) a body-centered cubic lattice, and (c) a face- centered cubic lattice? Assume the spheres to be of equal size.

Calculate the number of spheres in these unit cells simple cubic, body- centered cubic, and face-centerec cubic cells. Assume that the spheres are of equa size and that they are only at the lattice points.

Metallic iron crystallizes in a cubic lattice. The unit cell edge length is \(287 \mathrm{pm}\). The density of iron is \(7.87 \mathrm{~g} / \mathrm{cm}^{3}\). How many iron atoms are there within a unit cell?

Barium metal crystallizes in a body-centered cubic lattice (the Ba atoms are at the lattice points only). The unit cell edge length is \(502 \mathrm{pm},\) and the density of \(\mathrm{Ba}\) is \(3.50 \mathrm{~g} / \mathrm{cm}^{3}\). Using this information, calculate Avogadro's number. (Hint: First calculate the volume occupied by 1 mole of \(\mathrm{Ba}\) atoms in the unit cells. Next calculate the volume occupied by one of the Ba atoms in the unit cell.)

Vanadium crystallizes in a body-centered cubic lattice (the \(\mathrm{V}\) atoms occupy only the lattice points). How many \(\mathrm{V}\) atoms are in a unit cell?