A substance has a band gap of 6.9 eV at 273 K. Is this substance best classified as an insulator, a semiconductor, or a metal?

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Understand the concept of band gap: The band gap is the energy difference between the valence band and the conduction band in a material. It determines the electrical conductivity of the material.

Classify materials based on band gap: Metals have no band gap (or a very small one), semiconductors have a moderate band gap (typically 0.5 to 3 eV), and insulators have a large band gap (greater than 3 eV).

Analyze the given band gap: The problem states that the substance has a band gap of 6.9 eV.

Compare the given band gap to typical values: Since 6.9 eV is significantly greater than 3 eV, it falls into the range typical for insulators.

Conclude the classification: Based on the band gap value of 6.9 eV, classify the substance as an insulator.

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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 valence band and the conduction band in a material. It determines how easily electrons can be excited from the valence band to the conduction band, influencing the electrical conductivity of the material. A larger band gap typically indicates that a material is less conductive, as more energy is required to promote electrons.

Classification of Materials

Materials are classified based on their electrical conductivity into three main categories: conductors, semiconductors, and insulators. Conductors have little to no band gap, allowing easy electron flow; semiconductors have a moderate band gap, enabling conductivity under certain conditions; and insulators have a large band gap, preventing electron flow under normal conditions.

Temperature Effects on Band Gap

Temperature can influence the band gap of a material, often causing it to decrease as temperature increases. However, at low temperatures, such as 273 K, the intrinsic properties of the material are more pronounced. Understanding how temperature affects conductivity is crucial for determining the material's classification in practical applications.