An electron shell may be crudely thought of as an orbit followed by electrons around an atom nucleus. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Because each shell can contain only a fixed number of electrons, each shell is associated with a particular range of electron energy, and thus each shell must fill completely before electrons can be added to an outer shell. The electrons in the outermost shell determine the chemical properties of the atom (see valence shell). An electron shell may be crudely thought of as an Orbit followed by Electrons around an Atom nucleus. For an explanation of why electrons exist in these shells see electron configuration. In Atomic physics and Quantum chemistry, electron configuration is the arrangement of Electrons in an Atom, Molecule, or other [1]
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Orbital motions of electrons
Although it is common in diagrams to show electrons as objects following exact orbits like miniature planets, they actually move randomly and their so-called "orbits" represent only an average position. [2]
Shells
The electron shells are labelled K, L, M, N, O, P, and Q; or 1, 2, 3, 4, 5, 6, and 7; going from innermost shell outwards. Electrons in outer shells have higher average energy and travel further from the nucleus than those in inner shells, making them more important in determining how the atom reacts chemically and behaves as a conductor, etc, because the pull of the atom's nucleus upon them is weaker and more easily broken.
Subshells
Each shell is composed of subshells labeled s,p,d,and f; which are themselves composed of orbitals. An s subshell orbital can contain a maximum of two electrons. The first principle shell, K (or 1), has one subshell, the 1s shell. The second principal shell has two subshells, 2s and 2p. The third shell subshells designated 3s, 3p, and 3d, etc. [3]
Although it is commonly stated that all the electrons in a shell have the same energy, this is an approximation. However, the electrons in a subshell do have the same level of energy, with later subshells having more energy per electron that earlier ones. This effect is great enough that the energy ranges associated with shells can overlap - see "Valence shells" below.
Number of electrons in each shell
- Each s subshell holds no more than two electrons
- Each p subshell holds no more than six electrons
- Each d subshell holds no more than ten electrons
- Each f subshell holds no more than fourteen electrons
Therefore, the K shell, which contains only an s subshell, can hold up to 2 electrons; the L shell, which contains an s and a p, can hold up to 2+6=8 electrons; and so forth. The general formula is that the nth shell can in principle hold up to 2n2 electrons.
Although that formula gives the maximum in principle, in fact that maximum can only be achieved (by known elements) for the first four shells (K,L,M,N). In fact, no known element has more than 32 electrons in any one shell. [4][5] This is because the subshells are filled according to the Aufbau principle. The Aufbau principle (from the German Aufbau meaning "building up construction" also Aufbau rule or building-up principle) is The first elements to have more than 32 electrons in one shell would belong to the g-block of period 8 of the periodic table. The g-block is a hypothetical region in the Periodic table of the elements. A period 8 element is one of the Chemical elements in the eighth row (or period) of the (extended periodic table of the elements. The periodic table of the chemical elements is a tabular method of displaying the Chemical elements Although precursors to this table exist its invention is These elements would have some electrons in their 5g subshell and thus have more than 32 electrons in the O shell (fifth principal shell).
Valence shells
The valence shell is the outermost shell of an atom. In chemistry valence electrons are the Electrons contained in the outermost or valence, Electron shell of an Atom. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny It is usually (and misleadingly) said that the electrons in this shell make up its valence electrons, that is, the electrons that determine how the atom behaves in chemical reactions, where atoms with complete valence shells are the most chemical non-reactive, while those with only one electron in their valence shells (alkalis) or just missing one electron from having a complete shell (halogens) are the most reactive. In chemistry valence electrons are the Electrons contained in the outermost or valence, Electron shell of an Atom. In Chemistry, an alkali (from Arabic: Al-Qaly القلي القالي) is a basic, ionic salt of an Alkali metal Abundance Owing to their high Reactivity, the halogens are found in the environment only in compounds or as Ions Halide ions and oxoanions [6]
However, the real truth is more complicated. The electrons that determine how an atom reacts chemically are those that travel furthest from the nucleus - i. e. those with the most energy. As stated in "Subshells", electrons in the inner subshells have less energy than those in outer subshells. This effect is great enough so that the 3d electrons have more energy than 4s electrons, and are hence more important in chemical reactions, hence making them valence electrons although they are not in the so-called valence shell. [7]
See also Electron counting and 18-Electron rule. Electron counting is a formalism used for classifying compounds and for explaining or predicting electronic structure and bonding. The 18-electron rule is a Rule of thumb used primarily in transition metal chemistry for characterizing and predicting the stability of metal complexes
History
The existence of electron shells was first observed experimentally in Charles Barkla's and Henry Moseley's X-ray absorption studies. Charles Glover Barkla ( June 27, 1877 &ndash October 23, 1944) was an English physicist. Henry Gwyn Jeffreys Moseley ( November 23, 1887 – August 10, 1915) was an English physicist. X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Barkla labelled them with the letters K, L, M, N, O, P, and Q. (The origin of this terminology was alphabetic. K for hypothetical spectral lines that were never discovered. ) These letters were later found to correspond to the n-values 1, 2, 3, etc. They are used in the spectroscopic Siegbahn notation. The Siegbahn notation is used in X-ray spectroscopy to name the spectral lines that are characteristic to elements
The name for electron shells originates from the Bohr model, in which groups of electrons were believed to orbit the nucleus at certain distances, so that their orbits formed "shells" around the nucleus. In Atomic physics, the Bohr model created by Niels Bohr depicts the Atom as a small positively charged nucleus surrounded by Electrons
The physical chemist Gilbert Lewis was responsible for much of the early development of the theory of the participation of valence shell electrons in chemical bonding. Physical chemistry, is the application of Physics to macroscopic microscopic atomic subatomic and particulate phenomena in chemical systems It is mostly defined as a large Gilbert Newton Lewis ( October 23, 1875 - March 23, 1946) was a famous American physical chemist known for the discovery Linus Pauling later generalized and extended the theory while applying insights from quantum mechanics. Linus Carl Pauling (February 28 1901 – August 19 1994 was an American Scientist, Peace activist, Author and educator. Quantum mechanics is the study of mechanical systems whose dimensions are close to the Atomic scale such as Molecules Atoms Electrons