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Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. Atomic physics typically refers to the study of atomic structure and the interaction between atoms. It is primarily concerned with the way in which electrons are arranged 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 studies nuclear reactions and special properties of 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.
Isolated atoms
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 particles.
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.
Electronic configuration
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).
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 photon.
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.
Bohr Model of the Atom
The Bohr model, proposed by Niels Bohr in 1913, is a revolutionary theory describing the structure of the hydrogen atom. It introduced the idea of quantized orbits for electrons, combining classical and quantum physics.
Key Postulates of the Bohr Model
1.Electrons Move in Circular Orbits:
• Electrons revolve around the nucleus in fixed, circular paths called orbits or energy levels.
•These orbits are stable and do not radiate energy.
2.Quantization of Angular Momentum:
•The angular momentum of an electron is quantized and given by:
L = m_e v r = n\hbar, \quad n = 1, 2, 3, \dots
where:
• m_e : Mass of the electron.
• v : Velocity of the electron.
• r : Radius of the orbit.
• \hbar : Reduced Planck’s constant ( \hbar = \frac{h}{2\pi} ).
•n : Principal quantum number, representing the orbit.
3.Energy Levels:
•Each orbit has a specific energy. The total energy of an electron in the nth orbit is:
E_n = -\frac{13.6}{n^2} \ \text{eV},
where 13.6 \ \text{eV} is the ground-state energy of the hydrogen atom.
4.Emission or Absorption of Energy:
•Electrons can transition between orbits by absorbing or emitting energy equal to the difference between the energy levels:
\Delta E = E_f - E_i = h\nu,
where:
•h : Planck’s constant.
• \nu : Frequency of emitted/absorbed radiation.
• E_f, E_i : Final and initial energy levels.
History and developments
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 Vaiśeṣika Sūtra written by Kaṇāda. 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 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 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.
Beyond the well-known phenomena which can be describe with regular quantum mechanics chaotic processes can occur which need different descriptions.
Significant atomic physicists
- Pre quantum mechanics
- John Dalton
- Joseph von Fraunhofer
- Johannes Rydberg
- J. J. Thomson
- Ernest Rutherford
- Democritus
- Vaiśeṣika Sūtra
- Post quantum mechanics
- Alexander Dalgarno
- David Bates
- Niels Bohr
- Max Born
- Clinton Joseph Davisson
- Paul A. M. Dirac
- Enrico Fermi
- Charlotte Froese Fischer
- Vladimir Fock
- Douglas Hartree
- Ernest M. Henley
- Ratko Janev
- Daniel Kleppner
- Harrie S. Massey
- Nevill Mott
- I. I. Rabi
- Norman Ramsey
- Mike Seaton
- John C. Slater
- George Paget Thomson
See also
- Particle physics
- Isomeric shift
- Atomism
- Ionisation
- Quantum Mechanics
- Electron Correlation
- Quantum Chemistry
- Bound State
Bibliography
- Bransden, BH; Joachain, CJ (2002). Physics of Atoms and Molecules (2nd ed.). Prentice Hall. ISBN 978-0-582-35692-4.
- Sommerfeld, A. (1923) Atomic structure and spectral lines. (translated from German "Atombau und Spektrallinien" 1921), Dutton Publisher.
- Foot, CJ (2004). Atomic Physics. Oxford University Press. ISBN 978-0-19-850696-6.
- Smirnov, B.E. (2003) Physics of Atoms and Ions, Springer. ISBN 0-387-95550-X.
- Szász, L. (1992) The Electronic Structure of Atoms, John Willey & Sons. ISBN 0-471-54280-6.
- Herzberg, Gerhard (1979) [1945]. Atomic Spectra and Atomic Structure. New York: Dover. ISBN 978-0-486-60115-1.
- Bethe, H.A. & Salpeter E.E. (1957) Quantum Mechanics of One- and Two Electron Atoms. Springer.
- Born, M. (1937) Atomic Physics. Blackie & Son Limited.
- Cox, P.A. (1996) Introduction to Quantum Theory and Atomic Spectra. Oxford University Press. ISBN 0-19-855916
- Condon, E.U. & Shortley, G.H. (1935). The Theory of Atomic Spectra. Cambridge University Press. ISBN 978-0-521-09209-8.
- Cowan, Robert D. (1981). The Theory of Atomic Structure and Spectra. University of California Press. ISBN 978-0-520-03821-9.
- Lindgren, I. & Morrison, J. (1986). Atomic Many-Body Theory (Second ed.). Springer-Verlag. ISBN 978-0-387-16649-0.
References
- Demtröder, W. (2006). Atoms, molecules and photons : an introduction to atomic-, molecular-, and quantum-physics. Berlin: Springer. ISBN 978-3-540-32346-4. OCLC 262692011.
- Svanberg, S. (2004). Atomic and Molecular Spectroscopy. Springer. ISBN 3-540-20382-6.
- Bell, K.L.; Berrington, K.A.; Crothers, D.S.F.; Hilbert, A.; Taylor, K. (2002). Supercomputing, Collision Processes, and Applications. ISBN 0-306-46190-0.
- Amusia, M. Ya.; Chernysheva, L.V. (1997). Computation of Atomic Processes. Institute of Physics Publishing. ISBN 0-7503-0229-1.
- Blümel, R.; Reinhardt, W.P (1997). Chaos in Atomic Physics. Cambridge University Press. ISBN 0-521-45502-2.
External links
- MIT-Harvard Center for Ultracold Atoms
- Stanford QFARM Initiative for Quantum Science & Enginneering
- Joint Quantum Institute at University of Maryland and NIST
- Atomic Physics on the Internet
- JILA (Atomic Physics)
- ORNL Physics Division
This article includes a list of general references but it lacks sufficient corresponding inline citations Please help to improve this article by introducing more precise citations September 2015 Learn how and when to remove this message Atomic physics is the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus Atomic physics typically refers to the study of atomic structure and the interaction between atoms It is primarily concerned with the way in which electrons are arranged 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 studies nuclear reactions and special properties of 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 Isolated atomsAtomic 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 particles 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 Electronic configurationElectrons 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 photon 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 Bohr Model of the Atom The Bohr model proposed by Niels Bohr in 1913 is a revolutionary theory describing the structure of the hydrogen atom It introduced the idea of quantized orbits for electrons combining classical and quantum physics Key Postulates of the Bohr Model 1 Electrons Move in Circular Orbits Electrons revolve around the nucleus in fixed circular paths called orbits or energy levels These orbits are stable and do not radiate energy 2 Quantization of Angular Momentum The angular momentum of an electron is quantized and given by L m e v r n hbar quad n 1 2 3 dots where m e Mass of the electron v Velocity of the electron r Radius of the orbit hbar Reduced Planck s constant hbar frac h 2 pi n Principal quantum number representing the orbit 3 Energy Levels Each orbit has a specific energy The total energy of an electron in the nth orbit is E n frac 13 6 n 2 text eV where 13 6 text eV is the ground state energy of the hydrogen atom 4 Emission or Absorption of Energy Electrons can transition between orbits by absorbing or emitting energy equal to the difference between the energy levels Delta E E f E i h nu where h Planck s constant nu Frequency of emitted absorbed radiation E f E i Final and initial energy levels History and developmentsOne 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 Vaiseṣika Sutra written by Kaṇada 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 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 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 Beyond the well known phenomena which can be describe with regular quantum mechanics chaotic processes can occur which need different descriptions Significant atomic physicistsPre quantum mechanicsJohn Dalton Joseph von Fraunhofer Johannes Rydberg J J Thomson Ernest Rutherford Democritus Vaiseṣika SutraPost quantum mechanicsAlexander Dalgarno David Bates Niels Bohr Max Born Clinton Joseph Davisson Paul A M Dirac Enrico Fermi Charlotte Froese Fischer Vladimir Fock Douglas Hartree Ernest M Henley Ratko Janev Daniel Kleppner Harrie S Massey Nevill Mott I I Rabi Norman Ramsey Mike Seaton John C Slater George Paget ThomsonSee alsoParticle physics Isomeric shift Atomism Ionisation Quantum Mechanics Electron Correlation Quantum Chemistry Bound StateBibliographyBransden BH Joachain CJ 2002 Physics of Atoms and Molecules 2nd ed Prentice Hall ISBN 978 0 582 35692 4 Sommerfeld A 1923 Atomic structure and spectral lines translated from German Atombau und Spektrallinien 1921 Dutton Publisher Foot CJ 2004 Atomic Physics Oxford University Press ISBN 978 0 19 850696 6 Smirnov B E 2003 Physics of Atoms and Ions Springer ISBN 0 387 95550 X Szasz L 1992 The Electronic Structure of Atoms John Willey amp Sons ISBN 0 471 54280 6 Herzberg Gerhard 1979 1945 Atomic Spectra and Atomic Structure New York Dover ISBN 978 0 486 60115 1 Bethe H A amp Salpeter E E 1957 Quantum Mechanics of One and Two Electron Atoms Springer Born M 1937 Atomic Physics Blackie amp Son Limited Cox P A 1996 Introduction to Quantum Theory and Atomic Spectra Oxford University Press ISBN 0 19 855916 Condon E U amp Shortley G H 1935 The Theory of Atomic Spectra Cambridge University Press ISBN 978 0 521 09209 8 Cowan Robert D 1981 The Theory of Atomic Structure and Spectra University of California Press ISBN 978 0 520 03821 9 Lindgren I amp Morrison J 1986 Atomic Many Body Theory Second ed Springer Verlag ISBN 978 0 387 16649 0 ReferencesDemtroder W 2006 Atoms molecules and photons an introduction to atomic molecular and quantum physics Berlin Springer ISBN 978 3 540 32346 4 OCLC 262692011 Svanberg S 2004 Atomic and Molecular Spectroscopy Springer ISBN 3 540 20382 6 Bell K L Berrington K A Crothers D S F Hilbert A Taylor K 2002 Supercomputing Collision Processes and Applications ISBN 0 306 46190 0 Amusia M Ya Chernysheva L V 1997 Computation of Atomic Processes Institute of Physics Publishing ISBN 0 7503 0229 1 Blumel R Reinhardt W P 1997 Chaos in Atomic Physics Cambridge University Press ISBN 0 521 45502 2 External linksWikimedia Commons has media related to Atomic physics MIT Harvard Center for Ultracold Atoms Stanford QFARM Initiative for Quantum Science amp Enginneering Joint Quantum Institute at University of Maryland and NIST Atomic Physics on the Internet JILA Atomic Physics ORNL Physics Division
