Atomic physics is the field of physics that studies atoms as an
isolated system of electrons and an atomic nucleus. It is primarily
concerned with the arrangement of electrons around the nucleus and the
processes by which these arrangements change. This comprises ions,
neutral atoms and, unless otherwise stated, it can be assumed that the
term atom includes ions.
The term atomic physics can be associated with nuclear power and
nuclear weapons, due to the synonymous use of atomic and nuclear in
standard English. Physicists distinguish between atomic physics —
which deals with the atom as a system consisting of a nucleus and
electrons — and nuclear physics, which considers atomic nuclei
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.
1 Isolated atoms
2 Electronic configuration
3 History and developments
4 Significant atomic physicists
5 See also
8 External links
Atomic physics primarily considers atoms in isolation. Atomic models
will consist of a single nucleus that may be surrounded by one or more
bound electrons. It is not concerned with the formation of molecules
(although much of the physics is identical), nor does it examine atoms
in a solid state as condensed matter. It is concerned with processes
such as ionization and excitation by photons or collisions with atomic
While modelling atoms in isolation may not seem realistic, if one
considers atoms in a gas or plasma then the time-scales for atom-atom
interactions are huge in comparison to the atomic processes that are
generally considered. This means that the individual atoms can be
treated as if each were in isolation, as the vast majority of the time
they are. By this consideration atomic physics provides the underlying
theory in plasma physics and atmospheric physics, even though both
deal with very large numbers of atoms.
Electrons form notional shells around the nucleus. These are normally
in a ground state but can be excited by the absorption of energy from
light (photons), magnetic fields, or interaction with a colliding
particle (typically ions or other electrons).
In the Bohr model, the transition of an electron with n=3 to the shell
n=2 is shown, where a photon is emitted. An electron from shell (n=2)
must have been removed beforehand by ionization
Electrons that populate a shell are said to be in a bound state. The
energy necessary to remove an electron from its shell (taking it to
infinity) is called the binding energy. Any quantity of energy
absorbed by the electron in excess of this amount is converted to
kinetic energy according to the conservation of energy. The atom is
said to have undergone the process of ionization.
If the electron absorbs a quantity of energy less than the binding
energy, it will be transferred to an excited state. After a certain
time, the electron in an excited state will "jump" (undergo a
transition) to a lower state. In a neutral atom, the system will emit
a photon of the difference in energy, since energy is conserved.
If an inner electron has absorbed more than the binding energy (so
that the atom ionizes), then a more outer electron may undergo a
transition to fill the inner orbital. In this case, a visible photon
or a characteristic x-ray is emitted, or a phenomenon known as the
Auger effect may take place, where the released energy is transferred
to another bound electron, causing it to go into the continuum. The
Auger effect allows one to multiply ionize an atom with a single
There are rather 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.
History and developments
Main article: Atomic theory
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 that 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.
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
Vaisheshika Sutra written by Kanad. 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. At this stage, it wasn't 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 Mendeleev was another
great step forward.
The true beginning of atomic physics is marked by the discovery of
spectral lines 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. 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 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. Similar
technological advances in accelerators, detectors, magnetic field
generation and lasers have greatly assisted experimental work.
Significant atomic physicists
Pre quantum mechanics
Joseph von Fraunhofer
J. J. Thomson
Post quantum mechanics
Clinton Joseph Davisson
Charlotte Froese Fischer
Ernest M. Henley
Harrie S. Massey
I. I. Rabi
John C. Slater
George Paget Thomson
Bransden, BH; Joachain, CJ (2002).
Physics of Atoms and Molecules (2nd
ed.). Prentice Hall. ISBN 0-582-35692-X.
Foot, CJ (2004). Atomic Physics. Oxford University Press.
Herzberg, Gerhard (1979) . Atomic Spectra and Atomic Structure.
New York: Dover. ISBN 0-486-60115-3.
Condon, E.U. & Shortley, G.H. (1935). The Theory of Atomic
Spectra. Cambridge University Press. ISBN 0-521-09209-4.
Cowan, Robert D. (1981). The Theory of Atomic Structure and Spectra.
University of California Press. ISBN 0-520-03821-5.
Lindgren, I. & Morrison, J. (1986). Atomic Many-Body Theory
(Second ed.). Springer-Verlag. ISBN 0-387-16649-1.
Wikimedia Commons has media related to Atomic physics.
MIT-Harvard Center for Ultracold Atoms
Joint Quantum Institute at University of Maryland and NIST
Physics on the Internet
JILA (Atomic Physics)
Branches of physics
Quantum field theory
Physics in life science