Question

please describe in details how you categorize them based on properties and bonding of materials

Define a metal, semiconductor and an insulator. Consider the properties and bonding of each of these materials and categorize them as metals, semiconductors, or insulators: Bi, AIF3, CuZn, InP, P4, NaHCO3, CdS, SiO2

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Answer 1

Metals Metals are elements that have free electrons and partially filled valence bands, thus are good conductors of electricity. These have very low resistivity and very high conductivity. Their valence and conduction bands overlap each other. There is no Forbidden Energy Gap (Energy difference between Valence and conduction Band) i.e. E OeV. As the Temperature decreases, the number of electrons in conduction band increases thus decreasing resistivity and increasing conductivity. At absolute zero temperature, the metals act as a super conductor. alconductivity) 102- 10 s/m plresistivity) 10- 108Om Insulators Insulators have fully filled valence band and empty conduction band separated by a large Energy Band Gap (E,> 4eV). Because of this reason, their conductivity is low and have a very high resistance. Their conductivity increases with increase in temperature, as the electrons in valence band get enough energy so that they can jump to conduction band. alconductivity) ~101- 1019 S/m p(resistivity) 10-1019 Om Semiconductors Semiconductor includes both elements (Si, Ge) and Compounds (GaAs, Sic) have resistivity or conductivity values between those of metals and insulators. These have Energy Band Gap between metals and non-metals. Some electrons can jump to the empty conduction band by thermal or optical excitation Their conductivity also increases with increase in temperature, as the electrons in valence band get enough energy so that they can jump to conduction band. At absolute zero temperature, they act as an insulator. Eg: 1.1 eV for Si 0.67 eV for Ge 1.43 eV for GaAs ofconductivity) 10-10 5/m piresistivity) 105-106 Om

Bi (Bismuth): Bismuth is a brittle metal with a white, silver-pink hue. When deposited in sufficiently thin layers on a substrate, bismuth is a semiconductor, despite being a post-transition metal. AIF3 (Aluminium Trifluoride): Aluminium Trifluoride is an insulator in solid state but is conductive in molten state thus together with cryolite increases conductivity in aluminium electrolysis during aluminium refining. CuZn (Brass): Brass is an alloy of Cu and Zn and a Conductor of electricity. Its Conductivity is a function of Copper content in it with [95% Cu and 5 % Zn highest value of conductivity (57% IACS)] and [ 70 % Cu and 30% Zn with lowest conductivity (lowers to 22% IACS ) ]. InP (Indium Phosphide): It is a Semiconductor with Indium from 13 group and Phosphorus from 15 group. P4(Polymeric Phosphorus): White (P4) and Red Phosphorus (Palymeric) is insulator whereas Black Phosphorus conducts electricity. NaHC03 (Sodium BiCarbonate): It is not a conductor of electricity on its own in solid as well as molten state but conducts electricity when dissolved in liquid. Cas (Cadium Sulfide): It is a semiconductor with energy band gap of 2.42eV and its conductivity increases when irradia ted. SiO2 (Silica): It is an insulator.