Practice Problems

Questions on Bonding in Elemental Solids

• Why is electronegativity related to band gap size and directionality of bonds?

• Which element would you expect to have a larger band gap in the elemental solid, aluminum (Al) or sulfur (S)? Briefly, explain your reasoning.

(help)

Questions on Bands and the Conductivity Properties of the Elements

• Which would you expect to be a better insulator, bromine (Br) or iodine (I)? Briefly, explain your reasoning. (help)

• A scientist measures the conductivity of solid beryllium (Be), boron (B), and carbon (C). The scientist finds that beryllium is the best conductor, boron conducts electricity slightly, and carbon conducts very little electricity. Briefly, explain the observed differences in conductivity between these elements in terms of bands and the movement of electrons. (help)

Questions on Doping to Enhance Conductivity of Semiconductors

• State whether each of the following could be used to dope arsenic (As): gallium (Ga), phosphorus (P) and selenium (Se).  Explain your answer. (help)

• For each of the elements listed above that could be used to dope arsenic, state whether an n-type or p-type semiconductor is formed.  Explain your answer. (help)

Questions on How LEDs Emit Light

• Explain, in terms of the movement of electrons, why an LED cannot be made from the junction of pure silicon (a non-doped semiconductor) and silicon doped with phosphorus (an n-type semiconductor). (help)

• What element could the pure silicone in the question above be doped with, in order to produce an LED? Explain your answer. (help)