---
tags: [physics, electricity]
---

# Electrons

## Shells

Electrons orbit in concentric circuits around the nucleus of the atom. Each
orbit is called a **shell**.

Each shell can accommodate a maximum number of electrons. The shells are
designated by letters and filled in sequence moving out from the shell nearest
to the nucleus.

_The diagram below demonstrates shell naming conventions and the maximum number
of electrons per shell._

![](/img/valence-shell.svg)

## Valence

The outer shell called the **valence shell** and the number of electrons it
contains, the **valence**. This part of the atom is the most important from the
point of view of electricity because it is from here that electrons can escape
the atom and where electrons from other atoms may join.

> The farther the valence shell is from the nucleus, the less attraction the
> nucleus has on each valence electron. Thus the potential for the atom to gain
> or lose elections increases if the valence shell is not full and is located
> far enough away from the nucleus.

## Conductivity and insularity

The **conductivity** of a material is an expression of its capacity to channel
electrical charge. Where electrical charge is the _flow of free electrons from
one atom to another_. The **insularity** of a material is the opposite: its
_capacity to resist the flow of electrical charge_.

Electrons in the valence shell can gain energy from external forces. If these
electrons gain enough energy, they can leave the atom and become **free
electrons**, moving randomly from atom to atom.

We call materials that contain a large number of free electrons **conductors**.
In contrast **insulators** are atoms that stabilize themselves by absorbing
valence electrons from other atoms to fill their valence shells, eliminating the
free electrons.

> The propensity for the electrons within a conductor to move about and jump
> between atoms, swapping charge, is not something that is only activated when a
> voltage is applied. In fact, the electrons are always doing this, even in a
> piece of inert copper. The difference is they are doing it randomly and in all
> kinds of directions. It is only when a voltage is applied that the motion and
> exchange of electrons is forced in one consistent direction.

### Semiconductors

Semiconductive materials are midway between conductors and insulators: they are
neither good conductors or insulators but can be altered to function in the
manner of either.

## Ionization

Ionization is the process of atoms gaining and losing electrons.

When an atom has an equal number of protons and electrons it is said to be
**electrically balanced**.

A balanced atom that receives one or more extra electrons gives way to an
overall negative charge. An atom in this state is a **negative ion**. Conversely
if a balanced atom loses one or more electrons it becomes positively charged and
is thus called a **positive ion**.

> The process of ionization is a constitutive part of the flow of current but
> not the only part. We also must factor the force that triggers ionization and
> the resistance that impedes it.
