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The melting points for the second-series transition elements increase from \(1522^{\circ} \mathrm{C}\) for yttrium to \(2623{ }^{\circ} \mathrm{C}\) for molybdenum and then decrease to \(321{ }^{\circ} \mathrm{C}\) for cadmium. Account for the trend using band theory.

Define a semiconductor, and give three examples.

Tell what is meant by each of the following terms: (a) Valence band (b) Conduction band (c) Band gap (d) Doping

Draw the bands of MO energy levels and the electron population for: (a) A semiconductor (b) A metallic conductor Explain why a semiconductor has the lower electrical conductivity.

How does the electrical conductivity of a semiconductor change as the size of the band gap increases? Explain.

How does the electrical conductivity of a semiconductor change as the temperature increases? Explain.

Explain what an \(n\) -type semiconductor is, and give an example. Draw an MO energy-level diagram, and show the population of the valence band and the conduction band for an \(n\) -type semiconductor.

Explain what a \(p\) -type semiconductor is, and give an example. Draw an MO energy-level diagram, and show the population of the valence band and the conduction band for a \(p\) -type semiconductor.

Explain why germanium doped with phosphorus has a higher electrical conductivity than pure germanium.

Explain why silicon doped with gallium has a higher electrical conductivity than pure silicon.