Editing Atomic physics (section)

==History and developments==
{{Main|Atomic theory}}
One of the earliest steps towards atomic physics was the recognition that matter was composed
of ''atoms''. It forms a part of the texts written in 6th century BC to 2nd century BC, such as those of [[Democritus]] or ''{{Lang|sa-latn|[[Vaiśeṣika Sūtra]]}}'' written by {{Lang|sa-latn|[[Kaṇāda (philosopher)|Kaṇāda]]|italic=no}}.<ref>{{Cite book |last1=Pullman |first1=Bernard |title=The atom in the history of human thought |last2=Pullman |first2=Bernard |date=2001 |publisher=Oxford Univ. Press |isbn=978-0-19-515040-7 |location=Oxford}}</ref><ref>{{Cite book |last1=Kanada |url=https://archive.org/details/thevaiasesikasut00kanauoft/page/n7/mode/2up?view=theater |title=The Vaisesika sutras of Kanada. Translated by Nandalal Sinha |last2=Sankara Misra |last3=Chandrakanta Tarakalankara |last4=Jayanarayana Tarkapanchanana |date=1923 |publisher=Allahabad Panini Office |others=Robarts - University of Toronto}}</ref> This theory was later developed in the modern sense of the basic unit of a [[chemical element]] by the British chemist and physicist [[John Dalton]] in the 18th century.<ref>{{Cite book |last=Dalton |first=John |url=https://doi.org/10.1017/cbo9780511736407 |title=A New System of Chemical Philosophy |date=2010-09-16 |publisher=Cambridge University Press |doi=10.1017/cbo9780511736407 |isbn=978-1-108-01968-2}}</ref> At this stage, it was not clear what atoms were, although they could be described and classified by their properties (in bulk). The invention of the [[periodic system of elements]] by [[Dmitri Mendeleev]] was another great step forward.

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]].<ref>{{Cite book |last=Brand |first=John C. D. |title=Lines of light: the sources of dispersive spectroscopy, 1800 - 1930 |date=1995 |publisher=Gordon and Breach Publ |isbn=978-2-88449-162-4 |location=Luxembourg}}</ref> The study of these lines led to the [[Bohr atom model]] and to the birth of [[quantum mechanics]]. 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]].<ref>{{Cite book |last=Svanberg |first=S. |title=Atomic and Molecular Spectroscopy |publisher=Springer |year=2004 |isbn=3-540-20382-6}}</ref>

Since the [[World War II|Second World War]], both theoretical and experimental fields have advanced at a rapid pace. This can be attributed to progress in computing technology, which has allowed larger and more sophisticated models of atomic structure and associated collision processes.<ref>{{Cite book |last1=Bell |first1=K.L. |title=Supercomputing, Collision Processes, and Applications |last2=Berrington |first2=K.A. |last3=Crothers |first3=D.S.F. |last4=Hilbert |first4=A. |last5=Taylor |first5=K. |year=2002 |publisher=Springer |isbn=0-306-46190-0}}</ref><ref>{{Cite book |last1=Amusia |first1=M. Ya. |title=Computation of Atomic Processes |last2=Chernysheva |first2=L.V. |publisher=Institute of Physics Publishing |year=1997 |isbn=0-7503-0229-1}}</ref> Similar technological advances in [[Accelerator physics|accelerators]], detectors, magnetic field generation and [[laser]]s have greatly assisted experimental work.

Beyond the well-known phenomena which can be describe with regular quantum mechanics  [[Chaos theory|chaotic]] processes<ref>{{Cite book |last1=Blümel |first1=R. |title=Chaos in Atomic Physics |last2=Reinhardt |first2=W.P |publisher=Cambridge University Press |year=1997 |isbn=0-521-45502-2}}</ref> can occur which need different descriptions.