Ch.12 - Solids and Solid-State Materials

McMurry8th EditionChemistryISBN: 9781292336145Not the one you use?Change textbook

McMurry 8th Edition

Ch.12 - Solids and Solid-State Materials

Problem 22c

Chapter 12, Problem 22c

The following diagrams show the electron populations of the bands of MO energy levels for four different materials:

. (c) Tell whether the conductivity of each material increases or decreases when the temperature increases.

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Identify the type of material based on the electron population in the bands: insulator, semiconductor, or conductor.

For each material, observe the distribution of electrons in the valence band (red) and conduction band (blue).

Recall that in conductors, the conductivity decreases with increasing temperature due to increased electron scattering.

For semiconductors, the conductivity increases with increasing temperature as more electrons gain enough energy to jump from the valence band to the conduction band.

For insulators, the conductivity remains very low and does not significantly change with temperature.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Molecular Orbital Theory

Molecular Orbital (MO) Theory describes the behavior of electrons in molecules by combining atomic orbitals to form molecular orbitals. These orbitals can be filled with electrons and are categorized as bonding or antibonding. The arrangement of these orbitals influences the electrical properties of materials, including their conductivity.

Conductivity and Temperature Relationship

The conductivity of materials is often affected by temperature changes. In semiconductors, increasing temperature typically provides energy to electrons, allowing them to move from the valence band to the conduction band, thus increasing conductivity. Conversely, in some metals, increased temperature can lead to increased lattice vibrations, which may decrease conductivity.

Band Gap

The band gap is the energy difference between the valence band and the conduction band in a material. Materials with a small band gap, like semiconductors, can have their conductivity significantly affected by temperature, as thermal energy can promote electrons across the gap. In contrast, materials with a large band gap are generally insulators and show little change in conductivity with temperature.

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Textbook Question

The following compound undergoes a phase transition from the solid to the smectic liquid crystal phase at 121 °C. Upon further heating, the compound undergoes another transition to liquid phase at 131 °C.

(b) Which image represents the arrangement of molecules at 135 °C?

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Textbook Question

Titanium oxide crystallizes in the following cubic unit cell:

(b) What is the formula of titanium oxide?

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Textbook Question

The following diagrams show the electron populations of the bands of MO energy levels for four different materials: (a) Classify each material as an insulator, a semiconductor, or a conducting metal.

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Textbook Question

The following diagram represents the electron population ofthe bands of MO energy levels for elemental silicon:

(a) Identify the valence band, conduction band, and band gap.

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Textbook Question

Diagrams (1) and (2) are energy-level diagrams for two different LEDs. One LED emits red light, and the other emits blue light. Which one emits red, and which blue? Explain.(1)

(2)

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