As a material scientist with a focus on the properties of substances and their applications, I can provide a comprehensive explanation as to why rubber does not conduct electricity.

Rubber is a polymer, which is a long chain of repeating molecular units. The molecular structure of rubber is composed of carbon and hydrogen atoms, which are covalently bonded together. Covalent bonds involve the sharing of electrons between atoms, creating a stable electron distribution around each atom. In a covalent bond, the electrons are shared rather than being free to move throughout the material.

The key to electrical conductivity lies in the presence of free electrons. Metals, which are good conductors of electricity, have a sea of free electrons that are not tightly bound to any particular atom. These electrons are able to move freely throughout the metal, allowing for the flow of electric current when a voltage is applied.

In contrast, rubber lacks these free electrons. The electrons in rubber are localized within the covalent bonds and are not free to move around. This lack of free electrons means that there is no medium for the electric current to flow through, rendering rubber a non-conductor of electricity.

Additionally, the molecular structure of rubber contributes to its insulating properties. The long chains of rubber molecules are often tangled and disordered, which further impedes the movement of any electrons that might be present. This disordered arrangement creates a physical barrier to the flow of electrons, reinforcing rubber's insulating nature.

Another factor to consider is the presence of impurities or dopants in a material. In semiconductors, for example, the introduction of impurities can alter the material's electrical properties, allowing it to behave as either a conductor or an insulator depending on the amount of voltage applied. However, rubber is typically very pure and does not contain the impurities that would enable it to conduct electricity.

The temperature can also affect a material's ability to conduct electricity. As temperature increases, the movement of electrons within a material can increase, potentially enhancing conductivity. However, rubber's molecular structure is such that it does not respond to temperature changes in a way that would promote electrical conductivity.

In summary, rubber does not conduct electricity because it lacks free electrons, has a molecular structure that impedes electron movement, is typically pure without the impurities that could alter its electrical properties, and does not respond to temperature changes in a way that would enhance conductivity.

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If a material lacks these free electrons (also called conducting electrons)--as rubber does--it will not conduct electricity and is called an insulator. There are also in-between materials, called semi-conductors, which behave as a conductor or insulator, depending on the amount of voltage applied to the material.read more >>