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Shielding Effect
In chemistry, the shielding effect sometimes referred to as atomic shielding or electron shielding describes the attraction between an electron and the nucleus in any atom with more than one electron. The shielding effect can be defined as a reduction in the effective nuclear charge on the electron cloud, due to a difference in the attraction forces on the electrons in the atom. It is a special case of electric-field screening. This effect also has some significance in many projects in material sciences. Strength per electron shell or orbital The wider the electron shells are in space, the weaker is the electric interaction between the electrons and the nucleus due to screening. Further, because of differences in orbital penetration, we can order the screening strength, ''S'', that electrons in a given orbital (s, p, d, or f) provide to the rest of the electrons thus: S(\mathrm) > S(\mathrm) > S(\mathrm) > S(\mathrm) . Description In hydrogen, or any other atom in group 1 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they undergo during chemical reaction, reactions with other chemical substance, substances. Chemistry also addresses the nature of chemical bonds in chemical compounds. In the scope of its subject, chemistry occupies an intermediate position between physics and biology. It is sometimes called the central science because it provides a foundation for understanding both Basic research, basic and Applied science, applied scientific disciplines at a fundamental level. For example, chemistry explains aspects of plant growth (botany), the formation of igneous rocks (geology), how atmospheric ozone is formed and how environmental pollutants are degraded (ecology), the prop ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schrödinger Equation
The Schrödinger equation is a partial differential equation that governs the wave function of a non-relativistic quantum-mechanical system. Its discovery was a significant landmark in the development of quantum mechanics. It is named after Erwin Schrödinger, an Austrian physicist, who postulated the equation in 1925 and published it in 1926, forming the basis for the work that resulted in his Nobel Prize in Physics in 1933. Conceptually, the Schrödinger equation is the quantum counterpart of Newton's second law in classical mechanics. Given a set of known initial conditions, Newton's second law makes a mathematical prediction as to what path a given physical system will take over time. The Schrödinger equation gives the evolution over time of the wave function, the quantum-mechanical characterization of an isolated physical system. The equation was postulated by Schrödinger based on a postulate of Louis de Broglie that all matter has an associated matter wave. The equati ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
University Of Guelph
The University of Guelph (abbreviated U of G) is a comprehensive Public university, public research university in Guelph, Ontario, Canada. It was established in 1964 after the amalgamation of Ontario Agricultural College (1874), the MacDonald Institute (1903), and the Ontario Veterinary College (1922), and has since grown to an institution of almost 30,000 students (including those at the Humber campus, Ridgetown campus, off-campus degree enrolments, diploma enrolments and part-time students) and employs 830 full-time faculty (academic staff) as of fall 2019. It offers 94 undergraduate degrees, 48 graduate programs, and 6 associate degrees in many different disciplines. The university conducts a significant degree of research and offers a wide range of undergraduate, graduate, and professional degrees. According to the ''Journal of Hospitality & Tourism Research'', the university's Hospitality and Tourism Management program has Canada's highest research index. The faculty at t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
D-block Contraction
The d-block contraction (sometimes called scandide contraction) is a term used in chemistry to describe the effect of having full d orbitals on the period 4 elements. The elements in question are gallium, germanium, arsenic, selenium, bromine, and krypton. Their electronic configurations include completely filled d orbitals (d10). The d-block contraction is best illustrated by comparing some properties of the group 13 elements to highlight the effect on gallium. Gallium can be seen to be anomalous. The most obvious effect is that the sum of the first three ionization potentials of gallium is higher than that of aluminium, whereas the trend in the group would be for it to be lower. The second table below shows the trend in the sum of the first three ionization potentials for the elements B, Al, Sc, Y, and La. Sc, Y, and La have three valence electrons above a noble gas electron core. In contrast to the group 13 elements, this sequence shows a smooth reduction. Ot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lanthanide Contraction
The lanthanide contraction is the greater-than-expected decrease in atomic radii and ionic radii of the elements in the lanthanide series, from left to right. It is caused by the poor shielding effect of nuclear charge by the 4f electrons along with the expected periodic trend of increasing electronegativity and nuclear charge on moving from left to right. About 10% of the lanthanide contraction has been attributed to relativistic effects. A decrease in atomic radii can be observed across the 4f elements from atomic number 57, lanthanum, to 70, ytterbium. This results in smaller than otherwise expected atomic radii and ionic radii for the subsequent d-block elements starting with 71, lutetium. Jolly, William L. ''Modern Inorganic Chemistry'', McGraw-Hill 1984, p. 22 This effect causes the radii of transition metals of group 5 and 6 to become unusually similar, as the expected increase in radius going down a period is nearly cancelled out by the f-block insertion, and has ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Steric Effects
Steric effects arise from the spatial arrangement of atoms. When atoms come close together there is generally a rise in the energy of the molecule. Steric effects are nonbonding interactions that influence the shape (conformational isomerism, conformation) and chemical reaction, reactivity of ions and molecules. Steric effects complement electronic effects, which dictate the shape and reactivity of molecules. Steric repulsive forces between overlapping electron clouds result in structured groupings of molecules stabilized by the way that opposites attract and like charges repel. Steric hindrance Steric hindrance is a consequence of steric effects. Steric hindrance is the slowing of chemical reactions due to steric bulk. It is usually manifested in ''intermolecular reactions'', whereas discussion of steric effects often focus on ''intramolecular interactions''. Steric hindrance is often exploited to control selectivity, such as slowing unwanted side-reactions. Steric hindran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Noble Gas Compound
In chemistry, noble gas compounds are chemical compounds that include an element from the noble gases, group 8 or 18 of the periodic table. Although the noble gases are generally unreactive elements, many such compounds have been observed, particularly involving the element xenon. From the standpoint of chemistry, the noble gases may be divided into two groups: the relatively reactive krypton ( ionisation energy 14.0 eV), xenon (12.1 eV), and radon (10.7 eV) on one side, and the very unreactive argon (15.8 eV), neon (21.6 eV), and helium (24.6 eV) on the other. Consistent with this classification, Kr, Xe, and Rn form compounds that can be isolated in bulk at or near standard temperature and pressure, whereas He, Ne, Ar have been observed to form true chemical bonds using spectroscopic techniques, but only when frozen into a noble gas matrix at temperatures of or lower, in supersonic jets of noble gas, or under extremely high pressures with metal ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Effective Nuclear Charge
In atomic physics, the effective nuclear charge of an electron in a multi-electron atom or ion is the number of elementary charges (e) an electron experiences by the nucleus. It is denoted by ''Z''eff. The term "effective" is used because the shielding effect of negatively charged electrons prevent higher energy electrons from experiencing the full nuclear charge of the nucleus due to the repelling effect of inner layer. The effective nuclear charge experienced by an electron is also called the core charge. It is possible to determine the strength of the nuclear charge by the oxidation number of the atom. Most of the physical and chemical properties of the elements can be explained on the basis of electronic configuration. Consider the behavior of ionization energies in the periodic table. It is known that the magnitude of ionization potential depends upon the following factors: # The size of an atom # The nuclear charge; oxidation number # The screening effect of the inner she ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Core Charge
Core electrons are the electrons in an atom that are not valence electrons and do not participate as directly in chemical bonding. The nucleus and the core electrons of an atom form the atomic core. Core electrons are tightly bound to the nucleus. Therefore, unlike valence electrons, core electrons play a secondary role in chemical bonding and reactions by screening the positive charge of the atomic nucleus from the valence electrons. The number of valence electrons of an element can be determined by the periodic table group of the element (see valence electron): *For main-group elements, the number of valence electrons ranges from 1 to 8 (''n''s and ''n''p orbitals). *For transition metals, the number of valence electrons ranges from 3 to 12 (''n''s and (''n''−1)d orbitals). *For lanthanides and actinides, the number of valence electrons ranges from 3 to 16 (''n''s, (''n''−2)f and (''n''−1)d orbitals). All other non-valence electrons for an atom of that element are considere ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atomic Number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic number is also equal to the number of electrons. For an ordinary atom which contains protons, neutrons and electrons, the sum of the atomic number ''Z'' and the neutron number ''N'' gives the atom's atomic mass number ''A''. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the mass defect of the nucleon binding is always small compared to the nucleon mass, the atomic mass of any atom, when expressed in daltons (making a quantity called the " relative isotopic mass"), is within 1% ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Rutherford Backscattering Spectroscopy
Rutherford may refer to: Places Australia * Rutherford, New South Wales, a suburb of Maitland * Rutherford (Parish), New South Wales, a civil parish of Yungnulgra County Canada * Mount Rutherford, Jasper National Park * Rutherford, Edmonton, neighbourhood * Rutherford House, in Edmonton, Alberta * Rutherford Library, University of Alberta United Kingdom * Rutherford Appleton Laboratory, Oxfordshire United States * Rutherford, California, in Napa County * East Rutherford, New Jersey * Rutherford, New Jersey * Rutherford, Pennsylvania * Rutherford, West Virginia * Rutherford County, North Carolina * Rutherford County, Tennessee People * Rutherford (name), people with the surname or given name Fiction * Rutherford the Brave, a character from Gamehendge, the fictional setting for a number of songs by the rock band Phish * Rutherford, Ohio, fictional setting of the television series ''3rd Rock from the Sun'' * Cullen Stanton Rutherford, a character from the ''Dr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Slater's Rules
In quantum chemistry, Slater's rules provide numerical values for the effective nuclear charge in a many-electron atom. Each electron is said to experience less than the actual nuclear charge, because of shielding or screening by the other electrons. For each electron in an atom, Slater's rules provide a value for the screening constant, denoted by ''s'', ''S'', or ''σ'', which relates the effective and actual nuclear charges as :Z_= Z - s.\, The rules were devised semi-empirically by John C. Slater and published in 1930. Revised values of screening constants based on computations of atomic structure by the Hartree–Fock method were obtained by Enrico Clementi et al. in the 1960s. Rules Firstly, the electrons are arranged into a sequence of groups in order of increasing principal quantum number n, and for equal n in order of increasing azimuthal quantum number l, except that s- and p- orbitals are kept together. : s s,2p s,3p d s,4p d f s, 5p detc. Each group is given a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
