91Ó°ÊÓ

Europium crystallizes in a body-centered cubic lattice (the Eu atoms occupy only the lattice points). The density of Eu is \(5.26 \mathrm{~g} / \mathrm{cm}^{3} .\) Calculate the unit cell edge length in picometers.

Crystalline silicon has a cubic structure. The unit cell edge length is \(543 \mathrm{pm}\). The density of the solid is 2.33 \(\mathrm{g} / \mathrm{cm}^{3} .\) Calculate the number of \(\mathrm{Si}\) atoms in one unit cell.

A face-centered cubic cell contains \(8 \mathrm{X}\) atoms at the corners of the cell and \(6 \mathrm{Y}\) atoms at the faces. What is the empirical formula of the solid?

When \(X\) rays of wavelength \(0.090 \mathrm{nm}\) are diffracted by a metallic crystal, the angle of first-order diffraction \((n=1)\) is measured to be \(15.2^{\circ} .\) What is the distance (in pm) between the layers of atoms responsible for the diffraction?

The distance between layers in an \(\mathrm{NaCl}\) crystal is \(282 \mathrm{pm} . \mathrm{X}\) rays are diffracted from these layers at an angle of \(23.0^{\circ} .\) Assuming that \(n=1,\) calculate the wavelength of the \(\mathrm{X}\) rays in nanometers.

Describe and give examples of the following types of crystals: (a) ionic crystals, (b) covalent crystals, (c) molecular crystals, (d) metallic crystals.

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

A solid is hard, brittle, and electrically nonconducting. Its melt (the liquid form of the substance) and an aqueous solution containing the substance conduct electricity. Classify the solid.

A solid is soft and has a low melting point (below \(100^{\circ} \mathrm{C}\) ). The solid, its melt, and an aqueous 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.