77 lines
3.1 KiB
Markdown
77 lines
3.1 KiB
Markdown
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---
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tags: [physics, electricity]
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---
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# Electrons
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## Shells
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Electrons orbit in concentric circuits around the nucleus of the atom. Each
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orbit is called a **shell**.
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Each shell can accommodate a maximum number of electrons. The shells are
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designated by letters and filled in sequence moving out from the shell nearest
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to the nucleus.
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_The diagram below demonstrates shell naming conventions and the maximum number
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of electrons per shell._
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## Valence
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The outer shell called the **valence shell** and the number of electrons it
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contains, the **valence**. This part of the atom is the most important from the
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point of view of electricity because it is from here that electrons can escape
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the atom and where electrons from other atoms may join.
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> The farther the valence shell is from the nucleus, the less attraction the
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> nucleus has on each valence electron. Thus the potential for the atom to gain
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> or lose elections increases if the valence shell is not full and is located
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> far enough away from the nucleus.
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## Conductivity and insularity
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The **conductivity** of a material is an expression of its capacity to channel
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electrical charge. Where electrical charge is the _flow of free electrons from
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one atom to another_. The **insularity** of a material is the opposite: its
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_capacity to resist the flow of electrical charge_.
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Electrons in the valence shell can gain energy from external forces. If these
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electrons gain enough energy, they can leave the atom and become **free
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electrons**, moving randomly from atom to atom.
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We call materials that contain a large number of free electrons **conductors**.
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In contrast **insulators** are atoms that stabilize themselves by absorbing
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valence electrons from other atoms to fill their valence shells, eliminating the
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free electrons.
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> The propensity for the electrons within a conductor to move about and jump
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> between atoms, swapping charge, is not something that is only activated when a
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> voltage is applied. In fact, the electrons are always doing this, even in a
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> piece of inert copper. The difference is they are doing it randomly and in all
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> kinds of directions. It is only when a voltage is applied that the motion and
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> exchange of electrons is forced in one consistent direction.
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### Semiconductors
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Semiconductive materials are midway between conductors and insulators: they are
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neither good conductors or insulators but can be altered to function in the
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manner of either.
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## Ionization
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Ionization is the process of atoms gaining and losing electrons.
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When an atom has an equal number of protons and electrons it is said to be
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**electrically balanced**.
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A balanced atom that receives one or more extra electrons gives way to an
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overall negative charge. An atom in this state is a **negative ion**. Conversely
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if a balanced atom loses one or more electrons it becomes positively charged and
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is thus called a **positive ion**.
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> The process of ionization is a constitutive part of the flow of current but
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> not the only part. We also must factor the force that triggers ionization and
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> the resistance that impedes it.
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