What rule is based on observation of atomic spectra?
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Hund's rule of maximum multiplicity Hund's rule of maximum multiplicity is a rule based on observation of atomic spectra, which is used to predict the ground state of an atom or molecule with one or more open electronic shells. The rule states that for a given electron configuration, the lowest energy term is the one with the greatest value of spin multiplicity. This implies that if two or more orbitals of equal energy are available, electrons will occupy them singly before filling them in pairs. The rule, discovered by Friedrich Hund in 1925, is of important use in atomic chemistry, spectroscopy, and quantum chemistry, and is often abbreviated to Hund's rule, ignoring Hund's other two rules.
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Friedrich Hund Friedrich Hermann Hund (4 February 1896 – 31 March 1997) was a German physicist from Karlsruhe known for his work on atoms and molecules.
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Bloch spectrum The Bloch spectrum is a concept in quantum mechanics in the field of theoretical physics; this concept addresses certain energy spectra considerations.
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Differential optical absorption spectroscopy In atmospheric chemistry, differential optical absorption spectroscopy (DOAS) is used to measure concentrations of trace gases. When combined with basic optical spectrometers such as prisms or diffraction gratings and automated, ground-based observation platforms, what we have is a cheap and powerful means for the measurement of such trace gas species as ozone and nitrogen dioxide. Typical setups allow for detection limits corresponding to optical depths of 0.0001 along lightpaths of up to typically 15 km and thus allow for the detection also of weak absorbers, such as water vapour, Nitrous acid, Formaldehyde, Tetraoxygen, Iodine oxide, Bromine oxide and Chlorine oxide.
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Isotopic shift The isotopic shift (also called isotope shift) is the shift in various forms of spectroscopy that occurs when one nuclear isotope is replaced by another.
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Radiochemistry Radiochemistry is the chemistry of radioactive materials, where radioactive isotopes of elements are used to study the properties and chemical reactions of non-radioactive isotopes (often within radiochemistry the absence of radioactivity leads to a substance being described as being "inactive" as the isotopes are "stable"). Much of radiochemistry deals with the use of radioactivity to study ordinary chemical reactions. This is very different from radiation chemistry where the radiation levels are kept too low to influence the chemistry.
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Semi-empirical quantum chemistry method Semi-empirical quantum chemistry methods are based on the Hartree–Fock formalism, but make many approximations and obtain some parameters from empirical data. They are very important in computational chemistry for treating large molecules where the full Hartree–Fock method without the approximations is too expensive. The use of empirical parameters appears to allow some inclusion of electron correlation effects into the methods.
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OZI rule The OZI rule is a consequence of quantum chromodynamics (QCD) that explains why certain decay modes appear less frequently than otherwise might be expected. It was independently proposed by Susumu Okubo, George Zweig and Jugoro Iizuka in the 1960s.
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Elemental analysis Elemental analysis is a process where a sample of some material (e.g., soil, waste or drinking water, bodily fluids, minerals, chemical compounds) is analyzed for its elemental and sometimes isotopic composition. Elemental analysis can be qualitative (determining what elements are present), and it can be quantitative (determining how much of each are present). Elemental analysis falls within the ambit of analytical chemistry, the set of instruments involved in deciphering the chemical nature of our world.
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Micro-spectrophotometry Microspectrophotometry is the measure of the spectra of microscopic samples using different wavelengths of electromagnetic radiation (e.g. ultraviolet, visible and near infrared, etc.) It is accomplished with "microspectrophotometers", "cytospectrophotometers", "microfluorometers", "Raman microspectrophotometers", etc. A microspectrophotometer can be configured to measure transmittance, absorbance, reflectance, light polarization, fluorescence (or other types of luminescence such as photoluminescence) of sample areas less than a micrometer in diameter through a modified optical microscope.
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Visible-light astronomy Visible-light astronomy encompasses a wide variety of observations via telescopes that are sensitive in the range of visible light (optical telescopes). It includes "imaging", where a picture of some sort is made of the object; "photometry", where the amount of light coming from an object is measured, "spectroscopy", where the distribution of that light with respect to its wavelength is measured, and "polarimetry" where the polarisation state of that light is measured. An example of spectroscopy is the study of spectral lines to understand of what kind of matter light is going through. Visible astronomy also includes looking up at night (). Visible-light astronomy is part of optical astronomy, and differs from astronomies based on invisible types of light in the electromagnetic radiation spectrum, such as radio waves, infrared waves, ultraviolet waves, X-ray waves and gamma-ray waves.
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Spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies. Spectral lines are often used to identify atoms and molecules. These "fingerprints" can be compared to the previously collected "fingerprints" of atoms and molecules, and are thus used to identify the atomic and molecular components of stars and planets which would otherwise be impossible.
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Döbereiner's triads In the history of the periodic table, Döbereiner's triads were an early attempt to sort the elements into some logical order by their physical properties. In 1829, the German chemist Johann Wolfgang Döbereiner published a report of his previous observations that there were groups of three elements (hence "triads") which had similar physical properties. He also noted that some quantifiable properties of elements (e.g. atomic weight and density) in a triad followed a trend whereby the value of the middle element in the triad would be exactly or nearly predicted by taking the arithmetic mean of values for that property of the other two elements.
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Observation Observation is the active acquisition of information from a primary source. In living beings, observation employs the senses. In science, observation can also involve the recording of data via the use of instruments. The term may also refer to any data collected during the scientific activity. Observations can be qualitative, that is, only the absence or presence of a property is noted, or quantitative if a numerical value is attached to the observed phenomenon by counting or measuring.
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Mass spectrometry Mass spectrometry (MS) is an analytical technique that ionizes chemical species and sorts the ions based on their mass-to-charge ratio. In simpler terms, a mass spectrum measures the masses within a sample. Mass spectrometry is used in many different fields and is applied to pure samples as well as complex mixtures.
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Miller's Rule (optics) In optics, Miller's Rule is an empirical rule which gives an estimate of the order of magnitude of the nonlinear coefﬁcient.
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Pariser–Parr–Pople method In molecular physics, the Pariser–Parr–Pople method applies semi-empirical quantum mechanical methods to the quantitative prediction of electronic structures and spectra, in molecules of interest in the field of organic chemistry. Previous methods existed—such as the Hückel method which led to Hückel's rule—but were limited in their scope, application and complexity, as is the Extended Hückel method.
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Theoretical astronomy Theoretical astronomy is the use of the analytical models of physics and chemistry to describe astronomical objects and astronomical phenomena.
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Chemical property A chemical property is any of a material's properties that becomes evident during, or after, a chemical reaction; that is, any quality that can be established only by changing a substance's chemical identity. Simply speaking, chemical properties cannot be determined just by viewing or touching the substance; the substance's internal structure must be affected greatly for its chemical properties to be investigated. When a substance goes under a chemical reaction, the properties will change drastically, resulting in chemical change. However, a catalytic property would also be a chemical property.
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Chemical physics Chemical physics is a subdiscipline of chemistry and physics that investigates physicochemical phenomena using techniques from atomic and molecular physics and condensed matter physics; it is the branch of physics that studies chemical processes from the point of view of physics. While at the interface of physics and chemistry, chemical physics is distinct from physical chemistry in that it focuses more on the characteristic elements and theories of physics. Meanwhile, physical chemistry studies the physical nature of chemistry. Nonetheless, the distinction between the two fields is vague, and workers often practice in both fields during the course of their research.
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Atomic form factor In physics, the atomic form factor, or atomic scattering factor, is a measure of the scattering amplitude of a wave by an isolated atom. The atomic form factor depends on the type of scattering, which in turn depends on the nature of the incident radiation, typically X-ray, electron or neutron. The common feature of all form factors is that they involve a Fourier transform of a spatial density distribution of the scattering object from real space to momentum space (also known as reciprocal space). For an object that is spherically symmetric, the spatial density distribution can be expressed as a function of radius, formula_1, so that the form factor, formula_2, is defined as
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Metal L-edge Metal L-edge spectroscopy is a spectroscopic technique used to study the electronic structures of transition metal atoms and complexes. This method measures X-ray absorption caused by the excitation of a metal 2p electron to unfilled d orbitals (e.g. 3d for first-row transition metals), which creates a characteristic absorption peak called the L-edge. According to the selection rules, the transition is formally electric-dipole allowed, which not only makes it more intense than an electric-dipole forbidden metal K pre-edge (1s → 3d) transition, but also makes it more feature-rich as the lower required energy (~400-1000 eV from scandium to copper) results in a higher-resolution experiment.