State whether each is true or false and explain 1] isotactic polystyrene and ata

Question

State whether each is true or false and explain

1] isotactic polystyrene and atactic polystyrene are geometrical isomers.

2] holes in the band gap contribute to the elctrical conductivity of pure silicon

3] thick ropes made from spider silk proteins are a viable replacement for the steel cables that support the Golden Gate Bridge.

4] Embodied Energy and Life Cycle Assessment are useful concepts in the quest for sustainability.

5] The relative amounts of ferrite and cementite in a stainless steel dictate whether or not the stainless steel is magnetic.

Explanation / Answer

1] isotactic polystyrene and atactic polystyrene are geometrical isomers

ANS:false

2] holes in the band gap contribute to the elctrical conductivity of pure silicon

ans:true

reason: Both holes and electrons contribute equally to electrical conduction in pure silicon; conduction in phosphorus-doped silicon is due almost entirely to the motion of electrons. (The "extra" electron does leave behind a hole when it jumps into the conduction band, but the hole is not in a band with electrons around, so it does not move.) Electrons provide most of the current and are called the majority carrier. When the majority carrier is negative, the material is known as an n-type semiconductor. Since the phosphorus atom has "donated" an electron to the conduction band, phosphorus is called the donor material.   Any element with five valence electrons could theoretically serve as a donor for silicon and produce n-type behavior, but the number of valence electrons is not the only factor to consider. The size of the donor core, and how it fits into the lattice, has practical implications, as does the chemical properties of the donor. Finally, the distance between the donor energy level and the conduction band of the base material will determine how significant an effect the donor has on conductivity. Phosphorus and arsenic are used most commonly to dope silicon..

3] thick Copyropes made from spider silk proteins are a viable replacement for the steel cables that support the Golden Gate Bridge

ans:true

4] Embodied Energy and Life Cycle Assessment are useful concepts in the quest for sustainability.

ans:true

5] The relative amounts of ferrite and cementite in a stainless steel dictate whether or not the stainless steel is magnetic.

ans:true

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