Question

Lecture #7 homework check. None of the questions have answers in the back of the book, so I would like to swap answers. (A&E Chapter 8, problem 8 is colored, but the answer to problem 9 is in the back of my book.)

Answer 1

A&E Chapter 8 Answers

A&E 8-1) Electrons are shared between nuclei in covalent bonding. Electrons are transferred from one nucleus to another in ionic bonding. (One of nuclei monopolizes the electrons.)\[Mg^{2+}Cl^{-}_{2}\rightarrow ionic\]\[PF_5\rightarrow covalent\]I drew the Lewis dot structure of PF5.
http://www.tutor-pages.com/Chemistry/Molecular_Geometry/023_Phosphorus_Pentafluoride_PF5.html

A&E 8-7)
a) Electrostatic attractive forces are predominant when oppositely charged ions are far away.
b) By definition, attractive and repulsive forces are in balance when oppositely charged ions are at a distance of about r0.
c) Electron-electron repulsive forces predominate when oppositely charged ions are very very close together.

A&E 8-8) The lattice energy of an ionic compound can be calculated with the following equation:\[U=-k'(Q_1Q_2)/(r_0); 0<U\]U is the lattice energy. k' depends on the lattice configuration. Q1 and Q2 are the charges on the ions and r0 is the distance between the ions. All else being equal, larger value of r0, or bigger ions, result in a less stable compound. Higher charges and certain lattice configuration result in more stable compounds. (Does anyone have a better answer?)

A&E 8-11) Ionic compounds are hard solids with high melting points.

A&E 8-12) Electrostatic attraction extends in all directions, so ionic compounds form crystalline lattices instead of discrete pairs..

A&E 8-13) See answer for A&E 8-8.

A&E 8-14) Large anion + small cation. See answer for A&E 8-8.

A&E 8-17)\[a)Mg^{2+}\]\[b) Li^+\]\[c)Cu^{2+}\]See answer for A&E 8-8 for reasoning.

Answer 2

A&E Chapter 12 Answers

A&E 12-38) Ionic solids have higher melting points than molecular solids because electrostatic attraction with full charges is stronger than dipole-dipole bonding, London dispersion forces, hydrogen bond, etc.

A&E 12-40) You want to wind up with a material that has ionic bonding or strong covalent bonds. It should be a conductor, semi conductor or a solid electrolyte. Alternatively, you could take a conductor and give it a heat resistant coating. (Does anyone have a better answer?)

Answer 3

After discussing the question with the folks in the chemistry OpenStudy, I realized that the best answer for A&E Chapter 12 Problem 40 is probably a refractory metal or alloy tailored to your specific needs.
http://en.wikipedia.org/wiki/Refractory_metal