Editing Solid-state physics (section)

==Background==
Solid materials are formed from densely packed atoms, which interact intensely. These interactions produce the mechanical (e.g. [[hardness]] and [[Elasticity (physics)|elasticity]]), [[Heat conduction|thermal]], [[Electrical conduction|electrical]], [[Magnetism|magnetic]] and [[Crystal optics|optical]] properties of solids. Depending on the material involved and the conditions in which it was formed, the atoms may be arranged in a regular, geometric pattern ([[crystal|crystalline solids]], which include [[metal]]s and ordinary [[Ice|water ice]]) or irregularly (an [[amorphous solid]] such as common window [[glass]]).

The bulk of solid-state physics, as a general theory, is focused on [[crystal]]s. Primarily, this is because the periodicity of [[atom]]s in a crystal — its defining characteristic — facilitates mathematical modeling. Likewise, crystalline materials often have [[electrical engineering|electrical]], [[magnetism|magnetic]], [[optics|optical]], or [[mechanical engineering|mechanical]] properties that can be exploited for [[engineering]] purposes.

The forces between the atoms in a crystal can take a variety of forms. For example, in a crystal of [[sodium chloride]] (common salt), the crystal is made up of [[ion]]ic [[sodium]] and [[chlorine]], and held together with [[ionic bond]]s. In others, the atoms share [[electron]]s and form [[covalent bond]]s. In metals, electrons are shared amongst the whole crystal in [[metallic bond]]ing. Finally, the noble gases do not undergo any of these types of bonding. In solid form, the noble gases are held together with [[van der Waals force]]s resulting from the polarisation of the electronic charge cloud on each atom. The differences between the types of solid result from the differences between their bonding.