Atomic_physics

'''Atomic physics''' (or '''atom physics''') is the field of [[physics]] that studies atoms as an isolated system of [[electron]]s and an [[atomic nuclei|atomic nucleus]]. It is primarily concerned with the [[Electron configuration|arrangement of electrons around the nucleus]] and
the processes by which these arrangements change. This includes [[ions]] as well as neutral atoms and, unless otherwise stated, for the purposes of this discussion it should be assumed that the term ''atom'' includes ions.

The term ''atomic physics'' is often associated with [[nuclear power]] and [[nuclear bomb]]s, due to the [[synonym]]ous use of ''atomic'' and ''nuclear'' in [[standard English]]. However, physicists distinguish between atomic physics - which deals with the atom as
a system of electron(s) and a nucleus - and [[nuclear physics]] - which considers [[atomic nucleus|atomic nuclei]] alone.

As with many scientific fields, strict delineation can be highly contrived and atomic physics is often considered in the wider context of ''[[atomic, molecular, and optical physics]]''. Physics research groups are usually so classified.

== Isolated atoms ==

Atomic physics always considers atoms in ''isolation'' - i.e. a model will consist of a single nucleus which may be surrounded by one or more bound electrons. It is '''not''' concerned with the formation of [[molecule]]s (although much of the physics is identical) nor does it examine atoms in a [[solid state physics|solid state]] as [[condensed matter]]. It '''is''' concerned with processes such as
[[ionization]] and [[excitation]] by photons or collisions with atomic particles.

While modelling atoms in isolation may not seem realistic, if one considers atoms
in a [[gas]] or [[Plasma (physics)|plasma]] then the time-scales for
atom-atom interactions are huge in comparison to the atomic processes that we are concerned with.
This means that the individual atoms can be treated as if each were in isolation because
for the vast majority of the time they are. By this consideration atomic physics provides the underlying theory in [[plasma (physics)|plasma physics]] and [[atmospheric physics]]
even though both deal with huge numbers of atoms.

Additionally, the properties of an atom in isolation is different from that of individual atoms in relatively close proximity to each other. This is because medium and long range forces come into play with proximity.

== Electronic configuration ==

Electrons form notional [[Electron shells|shells]] around the nucleus. These are naturally in a [[ground state]] but can be excited
by the absorption of energy from light ([[photon]]s), magnetic fields, or interaction with a colliding particle (typically other electrons). The excited electron may still be bound to the nucleus
and should, after a certain period of time, decay back to the original ground state. The energy is released as a photon. There
are strict [[selection rules]] as to the electronic configurations that can be reached by excitation by light - however there are no such rules for excitation by collision processes.

An electron may be sufficiently excited so that it breaks free of the nucleus and is no longer part of the atom. The remaining system is an [[ion]] and the atom is said to have been [[ionized]] having been left in a charged state.

== History and developments ==
The majority of fields in physics can be divided between theoretical work and experimental work
and atomic physics is no exception. It is usually the case, but not always, that progress goes
in alternate cycles from an experimental observation, through to a theoretical explanation
followed by some predictions which may or may not be confirmed by experiment, and so on. Of course, the current state of technology at any given time can put limitations on what can be achieved experimentally and theoretically so it may take considerable time for theory to be refined.

{{Main|Atomic theory}}
Clearly the earliest steps towards atomic physics was the recognition that matter was composed
of ''atoms'', in the modern sense of the basic unit of a [[chemical element]]. This theory was developed by the British chemist and physicist [[John Dalton]] in the 18th century. At this stage, it wasn't clear what atoms were although they could be described and classified by their properties (in bulk) in a [[periodic table]].

{{Main|Basics of quantum mechanics}}
The true beginning of atomic physics is marked by the discovery of [[spectral line]]s and attempts to describe the phenomenon, most notably by [[Joseph von Fraunhofer]]. The study of these lines led to the [[Bohr atom model]] and to the birth of [[quantum mechanics]] itself. In seeking to explain atomic spectra an entirely new mathematical model of matter was revealed. As far as atoms and their electron shells were concerned, not only did this yield a better overall description, i.e. the [[atomic orbital model]], but it also provided a new theoretical basis for [[chemistry]]
([[quantum chemistry]]) and [[spectroscopy]].

Since the [[Second World War]], both theoretical and experimental fields have advanced at a great pace. This can be attributed to progress in computing technology which has allowed bigger and more sophisticated models of atomic structure and associated collision processes. Similar technological advances in accelerators, detectors, magnetic field generation and [[laser]]s have greatly assisted experimental work.



== Significant atomic physicists ==
; Pre quantum mechanics
* [[John Dalton]]
* [[Joseph von Fraunhofer]]
* [[Johannes Rydberg]]
* [[J.J. Thomson]]
; Post quantum mechanics
* [[David Bates (physicist)|David Bates]]
* [[Niels Bohr]]
* [[Max Born]]
* [[Clinton Joseph Davisson]]
* [[Charlotte Froese Fischer]]
* [[Vladimir Fock]]
* [[Douglas Hartree]]
* [[Harrie Massey|Harrie S. Massey]]
* [[Nevill Mott]]
* [[M. J. Seaton|Mike Seaton]]
* [[John C. Slater]]
* [[George Paget Thomson]]

== References ==
* {{cite book|title=Physics of Atoms and Molecules|author=Bransden, BH|coauthors=Joachain, CJ|
year=2002|publisher=Prentice Hall|edition=2nd Edition|id=ISBN 0-582-35692-X}}
* {{cite book|title=Atomic Physics|author=Foot, CJ|year=2004|
publisher=Oxford University Press|id=ISBN 0-19-850696-1}}

== External links ==
* [http://plasma-gate.weizmann.ac.il/API.html Atomic Physics on the Internet]
* [http://www-phys.llnl.gov/N_Div/atomic.html Atomic Physics Links]
* [http://jilawww.colorado.edu/research/atomic.html JILA (Atomic Physics)]
* [http://www.phy.ornl.gov ORNL Physics Division]

[[Category:Atomic physics| ]]
[[Category:Atomic, molecular, and optical physics]]



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