Textbook Question
The melting points for the second-series transition elements increase from 1522 °C for yttrium to 2623 °C for molybdenum and then decrease to 321 °C for cadmium. Account for the trend using band theory.
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Ch.12 - Solids and Solid-State Materials
McMurry8th EditionChemistryISBN: 9781292336145
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Table of contents
- Ch.1 - Chemical Tools: Experimentation & Measurement170
- Ch.2 - Atoms, Molecules & Ions160
- Ch.3 - Mass Relationships in Chemical Reactions169
- Ch.4 - Reactions in Aqueous Solution199
- Ch.5 - Periodicity & Electronic Structure of Atoms102
- Ch.6 - Ionic Compounds: Periodic Trends and Bonding Theory92
- Ch.7 - Covalent Bonding and Electron-Dot Structures61
- Ch.8 - Covalent Compounds: Bonding Theories and Molecular Structure59
- Ch.9 - Thermochemistry: Chemical Energy122
- Ch.10 - Gases: Their Properties & Behavior155
- Ch.11 - Liquids & Phase Changes54
- Ch.12 - Solids and Solid-State Materials73
- Ch.13 - Solutions & Their Properties120
- Ch.14 - Chemical Kinetics98
- Ch.15 - Chemical Equilibrium125
- Ch.16 - Aqueous Equilibria: Acids & Bases110
- Ch.17 - Applications of Aqueous Equilibria147
- Ch.18 - Thermodynamics: Entropy, Free Energy & Equilibrium86
- Ch.19 - Electrochemistry154
- Ch.20 - Nuclear Chemistry96
- Ch.21 - Transition Elements and Coordination Chemistry156
- Ch.22 - The Main Group Elements187
- Ch.23 - Organic and Biological Chemistry51
Chapter 12, Problem 77
Tell what is meant by each of the following terms.(c) Band gap
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The 'band gap' is a fundamental concept in solid-state physics and chemistry, particularly relevant to the study of semiconductors and insulators.
In a solid, electrons occupy energy levels that form bands. The 'valence band' is the highest range of electron energies where electrons are normally present at absolute zero temperature.
Above the valence band is the 'conduction band', which is the range of electron energies higher than those in the valence band. Electrons in this band are free to move and conduct electricity.
The 'band gap' is the energy difference between the top of the valence band and the bottom of the conduction band. It represents the energy required to move an electron from the valence band to the conduction band.
Materials with a large band gap are typically insulators, while those with a smaller band gap are semiconductors. Conductors have overlapping valence and conduction bands, resulting in no band gap.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Band Gap
The band gap is the energy difference between the top of the valence band and the bottom of the conduction band in a solid material. It determines the electrical conductivity of the material; a large band gap indicates an insulator, while a small band gap suggests a semiconductor or conductor. The band gap plays a crucial role in the optical and electronic properties of materials, influencing their behavior in devices like solar cells and LEDs.
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Valence Band
The valence band is the highest energy band that is fully occupied by electrons at absolute zero temperature. It contains the electrons that are involved in bonding and determines the chemical properties of the material. The position of the valence band relative to the conduction band is essential for understanding a material's electrical properties, particularly in semiconductors and insulators.
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Conduction Band
The conduction band is the range of energy levels that electrons can occupy when they are free to move and conduct electricity. It is typically unoccupied at absolute zero but can be populated by thermal energy or doping in semiconductors. The ability of electrons to transition from the valence band to the conduction band, overcoming the band gap, is fundamental to the electrical conductivity and overall behavior of materials.
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Related Practice
Textbook Question
Tungsten is hard and has a very high melting point (3422 °C), and gold is soft and has a relatively low melting point (1064 °C). Are these facts in better agreement with the electron-sea model or the MO model (band theory)? Explain.
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Textbook Question
Explain why the enthalpy of vaporization of vanadium (460 kJ/mol) is much larger than that of zinc (114 kJ/mol).
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Textbook Question
Draw the bands of MO energy levels and the electron population for: (a) A semiconductor (b) An electrical insulator Explain why a semiconductor has the higher electrical conductivity.
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Textbook Question
Classify the following semiconductors as n-type or p-type. (a) Si doped with In (b) Ge doped with Sb (c) Gray Sn doped with As
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Textbook Question
Write a balanced equation for the synthesis of the 2–6 semiconductor ZnTe by chemical vapor deposition from dimethylzinc, Zn(CH3)2, and diethyltellurium, Te(CH2CH3)2, assuming that the other product is gaseous propane (CH3CH2CH3).
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