How do the appearances of metals, semiconductors and insulators differ? Why?

Explain the following observation Both carbon and  aluminium are solids, and aluminium form sheets whereas carbon breaks into pieces when hammered.

Subject- Chemistry

a) Explain the band structure of an electrical conductor (metal), a semiconductor, and an insulator at 0 K by showing the valence and conduction bands and fermi energy levels. Explain how the electrical conduction takes place in these three types of materials. Give an example for each type of material. b)Explain what n and p-type semiconductors are using their band structures. Why?

Polycarbonate is sometimes used for protective helmets, such as motorcycle helmets. However, it is often not advisable to apply adhesive stickers to the helmet surface or to clean the surface with a solvent, as both can potentially degrade the helmet strength. Why might this be?

The figure to the right shows sunlight intensity as a function of wavelength. Answer the following questions about materials that could act as the absorber (p-type semiconductor) in a heterojunction solar cell. a.What advantage would there be in using a 1000-nm wavelength bandgap absorber vs. one that had a 400-nm wavelength bandgap? (HINT: the bandgap is the minimum energy required to promote electrons.) b. One reason the electron-volt (eV) is often used as the bandgap unit in solar cell research is that the bandgap in eV is also equal to the maximum voltage that can be generated by the solar cell. With this in mind, what advantage would there be in using a 400-nm wavelength bandgap absorber vs. one that had a 1000-nm wavelength bandgap? c.In light of your answers to (a) and (b), can there be one “best” bandgap to use in a solar cell?

Most semiconductors are found in what area of the periodic table? A) the representative element B) column 18, or viiia C) period 3 D) The carbon family, column 14 or Iva

Use molecular orbital band diagrams to explain why metals are good conductors but semiconductors are not.

2. A fine white powder has a melting point of 155°C (relatively low). It does not dissolve in water and does not conduct electricity, either dissolved in water or not. What is it? (Metallic, ionic, molecular solid, or network solid) Metallic lonic Molecular solid Network solid

Shown below is a key diagram that helps to explain silica-based glass. Describe this diagram as completely as you can (it has a distinctive name that includes chemical information and shape information). What does each sphere represent? Where are the bonding electrons located? Show them in this diagram.