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Topic: 18 electron rule

	Electron counting - Wikipedia, the free encyclopedia
		Electron counting is a formalism used for classifying compounds and for explaining or predicting electronic structure and bonding.
		Octet rule for main group elements, especially the lighter ones such as carbon, nitrogen, and oxygen.
		Eighteen electron rule in inorganic chemistry and organometallic chemistry of transition metals,
	en.wikipedia.org /wiki/Electron_counting (1042 words)

	Electron affinity - Wikipedia, the free encyclopedia
		In chemistry, electron affinity is the amount of energy absorbed when an electron is added to a neutral isolated gaseous atom to form a gaseous ion with a -1 charge.
		Electron affinity is influenced by the octet rule.
		For instance the electron affinity for benzene is positive, that of naphthalene near zero and that of anthracene positive.
	en.wikipedia.org /wiki/Electron_affinity (372 words)

	Octet rule - Wikipedia, the free encyclopedia
		The octet rule is a simple chemical theory that states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, similar to the electronic configuration of a noble gas.
		Hydrogen only needs one additional electron (for a total of two), to have a noble gas structure (that of helium; the duet rule of the first shell).
		The octet rule is inapplicable to atoms in periods greater than 2 because their electron shells can hold more than eight electrons.
	en.wikipedia.org /wiki/Octet_rule (342 words)

	The 18 electron rule (Site not responding. Last check: 2007-10-18)
		The 18 electron: A stable complex (with electron configuration of the next highest noble gas) is obtained when the sum of the metal d-electrons, electron donated from the ligand, and the overall charge of the complex equals 18
		The sum of all the electrons would assume a noble gas configuration of Kr, Xe or Rn.As with most rules of the thumb, the 18 electron rule is not always obeyed.
		18 electrons are required to fill 5 d-orbitals, 1 s-orbital and 3 p-orbitals of a transition metal and hence reach the configuration of a noble gas.
	easyweb.easynet.co.uk /~miky/projtpag/pag3.htm (374 words)

	International Union of Pure and Applied Chemistry
		Electron-counting rules - Rules establishing correspondence between the topology of a molecular structure and the number of electrons which may be placed into its bonding molecular orbitals.
		In the origin of various electron-counting rules lies a general assumption that the completeness of the valence electron shell of a molecular entity belonging to a certain structural type serves as the major criterion of structural stability.
		Electronic configuration - The allocation of electrons within an atom or a molecule to a set of correspondingly atomic or molecular orbitals complying with the Pauli exclusion principle.
	www.iupac.org /reports/1999/7110minkin/e.html (1852 words)

	The 18e rule (Site not responding. Last check: 2007-10-18)
		The 18 electron rule enable us to decide whether a d-block organometallic complex is likely to be stable.
		Each derives from a simple count of the number of electrons that may be acccomodated by the available valence orbitals - one s and three p for organic chemists - organometallic chemists count additionally the five d-orbitals in which to place their electrons.
		There are two distinct methods that are used to count electrons, the covalent or neutral method and the effective atomic number or ionic method.
	www.chem.ox.ac.uk /icl/dermot/organomet98/electroncounting/18erule.html (203 words)

	C&EN: SCIENCE & TECHNOLOGY - ELECTRON COUNTING CONTINUES TO ADD UP
		The rule is expected to be a useful extension of Wade's rule to cover condensed polyhedral boranes and the many possible products created by merging boranes and metallocenes into single macromolecules.
		However, these rules don't readily apply to electron-deficient molecules such as boranes that utilize multicentered bonding--a pair of electrons shared between more than two atoms--so other rules have been formulated.
		mno rule when condensation of two compounds is restricted to edge sharing in two dimensions, such as in polycyclic aromatic hydrocarbons.
	ipc.iisc.ernet.in /~jemmis/CnEN.html (911 words)

	Organometallic Mechanisms (Site not responding. Last check: 2007-10-18)
		Many transition metal complexes containing organic, carbonyl or hydride ligands, which are isolable at room temperature, can be regarded as having 18 electrons in the valence shell of the metal.
		In this way, the metal formally attain the electron configuration of the next higher noble gas [18 valence electron rule is often paraphrased as the inert gas rule, effective atomic number (EAN) rule].
		Take the number of electrons in the valence shell of the uncomplexed metal atom and add or subtract electrons according tot he total charge on the metal complex.
	www.chem.ox.ac.uk /icl/dermot/aus98/lecture1/slide2.html (124 words)

	The Organometallic HyperTextBook: Electron Counting
		Each derives from a simple count of the number of electrons that may be accommodated by the available valence orbitals (one s and three p for organic chemists; organometallic chemists get five bonus d-orbitals in which to place their electrons).
		The basic premise of this method is that we remove all of the ligands from the metal and, if necessary, add the proper number of electrons to each ligand to bring it to a closed valence shell state.
		Therefore, the methyl group is a one electron donor, not a two electron donor as it is under the ionic formalism.
	www.ilpi.com /organomet/electroncount.html (1139 words)

	E
		The number of nonbonded electrons at the metal plus the number of electrons in the metal-ligand bonds should be 18.
		The 18 electron rule in transition metal chemistry is a full analogue of the "Lewis octet rule".
		A molecular polarizability effect occurring by an intramolecular electron displacement (sometimes called the "conjugative mechanism" and, previously, the "tautomeric mechanism") characterized by the substitution of one electron pair for another within the same atomic octet of electrons.
	www.chem.qmul.ac.uk /iupac/gtpoc/E.html (2409 words)

	How long before superintelligence?
		A compromise would be to write some of the gates with an electron beam, especially at bottlenecks where speed is absolutely crucial, and use optical or EUV to write the other elements of the chip.
		If after 18 months the hardware were upgraded to double the speed, we would have an AI that could think twice as fast as its original implementation.
		But as a general rule, the intellectual achievements of artificial intellects are additive in a way that human achievements are not, or only to a much less degree.
	www.nickbostrom.com /superintelligence.html (6953 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		Title : Electron Spin Resonance in the Undergraduate Curriculum Abstract : The treatment of odd-electron species in the undergraduate curriculum includes discussion of radicals in organic chemistry and transition metal-containing compounds in both the inorganic and biochemistry lecture sequences.
		Although discussion of inorganic compounds with unpaired electrons is a vital component of the undergraduate chemistry syllabus, radicals are often quickly dismissed in the undergraduate organic chemistry curriculum as short-lived intermediates, ignoring the existence of stable radicals, and missing the opportunity to reinforce concepts in structure and bonding.
		Unfortunately, direct experimental evidence for odd-electron species and their reactivity are not usually presented at all.
	www.cs.utexas.edu /users/yguan/NSFAbstracts/Abstracts/EHR/DUE.EHR.a9850991.txt (240 words)

	CHEM 404/504 - INORGANIC CHEMISTRY (Site not responding. Last check: 2007-10-18)
		R and ethylene are isomerized to CH R using these "W=CH " units as the catalyst.
		Indicate formal oxidation state and valence electron count for all species proposed.
		In these cases, define what the hapticity should be in order that the compound obey the 18-electron rule.
	www.chem.arizona.edu /~floresm/CHEM404/exams/exam395.html (488 words)

	Chemistry 2 Course Web Site - Lecture Courses - Organometallic Chemistry (Site not responding. Last check: 2007-10-18)
		To introduce the 18 electron rule and its applications.
		Application of the 18 electron rule to metal carbonyl complexes.
		An ability to apply the 18 electron rule to simple complexes.
	www.chem.ed.ac.uk /teaching/undergrad/chemistry2/lectures/organometallic.html (168 words)

	Valence electrons. - Page 3
		This is a total of TWO valence electrons for each H atom in the water molecule.
		Hydrogen is an exception to this rule, because it can only donate one electron, but if you notice, every atom that has more than two electrons fills up the lowest shell with, always, two electrons.
		So, the main group "follows" the 8-electron rule AKA the octet rule, which is often broken.
	www.physicsforums.com /showthread.php?t=32409&page=3&pp=15 (2089 words)

	Chpt 10.html
		A. The s Bonding in ML We shall refer to L as any generic two electron s donating ligand.
		This is a system that will be stable for 12 electrons as well as 18 depending upon wether the nonbonding t
		These can easily be added to the basic electronic structure from the s system by interaction with the t
	www.chem.uh.edu /Courses/Albright/Chem6312/ch10/chpt10.html (798 words)

	A Half-Century of Nonclassical Organometallic Chemistry: A Personal Perspective (Site not responding. Last check: 2007-10-18)
		If the 18-electron rule were to be respected, only one of two structures, Figure 3a or 3b, could be proposed for it.
		As our work on fluxional metal polyolefin compounds proceeded, it became evident to me that clear discussion of the bonding and structures of these molecules was often hampered by the lack of a systematic notation to differentiate one mode of attachment of the olefin from another.
		The importance of concertedness is that all metal atoms at all times retained their preferred complement (usually 18) of electrons.
	pubs.acs.org /cgi-bin/jtextd?inocaj/41/4/html/ic010972n.html (9119 words)

	[No title]
		2) Organom= etallic complexes are often said to adhere to the 18 electron rule.
		What is the 18 electron rule and w= hy is 18 a desirable number of valence electrons?
		For each metal complex provide the coordination number, oxidation number and electron count to illustrate how these properties change over the course of your reaction scheme.
	www.chem.vt.edu /chem-dept/brewer/chem-ed/2004-5404/HW6.mht (359 words)

	[No title] (Site not responding. Last check: 2007-10-18)
		[6 marks] (b) Give examples of THREE complexes which obey the 16 electron rule and give a rationale for the 16 electron rule using a molecular orbital energy level diagram to illustrate your answer.
		[7 marks] (c) ‘The 16/18 electron rule is not always obeyed by transition metal complexes’.
		Giving appropriate examples, discuss this comment including in your answer reference to the following factors (i) type of ligand, (ii) position of the metal in the d block of the periodic table, (iii) the valency of the metal.
	www.gre.ac.uk /schools/cls/CHEM0627_2003.doc (434 words)

	Organic Cume - January 25, 1997
		Halogenated aromatic compounds are reluctant to undergo nucleophilic substitution.
		Higher number of electron withdrawing groups facilitate the nucleophilic displacement.
		State the 18 electron rule and explain it with the help of an example.
	www.ndsu.nodak.edu /instruct/grcook/orgcume/Jan-25-1997/OC-jan251997.html (352 words)

	Valence electrons
		Its chemical inertness is a consequence of the filled valence shell - to either remove or attach an electron is far too costly in terms of the energetics.
		The 8 electron rule is only valid for atoms and molecules in the early part of the periodic table (excluding, of course, hydrogen and helium).
		If you should in the course of your life study inorganic and organometallic chemistry, you will find mention of an "18-electron rule," which states that 18 valence electrons is the desired end result.
	www.physicsforums.com /showthread.php?mode=hybrid&t=35069 (382 words)

	[No title]
		Ñi¬ (ðH ðH ð0“”Þ½h¿ÿ ?ð ÿÿÿ»àã33Ìî‘ï Að90ððÑð( ð ððl ð CðÌ¹¿ÿðÐÿ°Ð°ðÃ ¹ ð ðð8 ð@`Ð ðð`ðZ ð sðÿÌf¿ÀÿðÀð Ðð]¢ ð ð0 ¹¿¿Àÿð@` ðõ¨Recall that for MAIN GROUP elements the octet rule* is used to predict the formulae of covalent compounds.
		Think about Na+ and Cl- This rule assumes that the central atom in a compound will make bonds such that the total number of electrons around the central atom is 8.
		This rule is only valid for Period 2 nonmetallic elements.¡j6
	www.chem.ualberta.ca /~chem33x/chandouts/lecture18_files/lecture18.ppt (345 words)

	Review for Exam Two
		Physical properties and electron configurations of d block metals; lanthanoid contraction; colors of ionic compounds and d electron configurations, color wheel; paramagnetism and diamagnetism; variable oxidation states; review of coordination numbers, CN = 2, 3, 4, 5, 6 covered previously (see Ch.
		configurations; selection rules (spin and Laporte), forbidden and allowed transitions and examples; Orgel diagrams; Term symbols for ground states (handout); brief magnetic properties (mu effective, Gouy balance, paramagnetism and diamagnetism, ferro-, antiferro- and ferri-magnetism, superexchange).
		; 18 electron rule and ligand electron donors.
	www.lycoming.edu /chem/spring2004/333/examreview3.htm (1153 words)

	Tuesday, Jan
		The 18 electron rule is to organometallic chemistry
		With a recent inorganic Chemistry student as guide (you know who you are!), rediscover the development of the MOT diagram for octahedral ML
		Can you formulate a general rule about the relationship of coordination number, metal electrons and carbonyl complex stability?
	www.brynmawr.edu /Acads/Chem/sburgmay/chem332/TuesdayJan23.html (168 words)

	Study Questions (Site not responding. Last check: 2007-10-18)
		(16.6) Based on electronic effects, suggest a mechanism for the substitution reaction of Cr(CO)
		(16.6) Diagram the flow of electrons for the reaction on the bottom of page 679.
		(16.7) Prepare a table giving the name, structure, binding mode and electron donating capability for the 7 types of hydrocarbon ligands.
	www.users.csbsju.edu /~amckenna/341,16study.html (390 words)

	Atomic Structure
		Included is the description of filling subshells with electrons.
		Includes definitions of coordination chemistry and the 18-electron rule.
		Rules for bond angles and geometries allow representations of structures.
	dwb.unl.edu /Teacher/NSF/C10/C10Links/chemistry.about.com/msub39.htm (494 words)

	CHEM 404/504 - INORGANIC CHEMISTRY (Site not responding. Last check: 2007-10-18)
		which could explain the presence of one unpaired electron.
		Cytochrome c is an electron transfer protein in which the iron undergoes reversible 1-electron oxidation and reduction without changing its ligation.
		The axial ligands bound to Fe in this protein are a histidine (N-donor) and a methionine (S-donor).
	www.chem.arizona.edu /~floresm/CHEM404/exams/final95.html (1097 words)

	Electronic Structure
		Bringing a strong magnet close to each capsule will produce the largest response from the Mn sample (5 unpaired electrons), next largest response from the Co sample (3 unpaired electrons), and negligible response from the Zn sample (diamagnetic).
		II, III, IV 3048) Photo-excitation promotes an electron from the HOMO (highest occupied molecular orbital) to the LUMO (lowest unoccupied molecular orbital) of a molecule (see diagram below).
		Which arrow shown below represents the electronic transition corresponding to the ionization of N? According to LeChatlier's Principle, adding boron (an acceptor) to N-doped diamond will shift the equilibrium of equation 1 toward the:
	jchemed.chem.wisc.edu /JCEDlib/QBank/collection/ConcepTests/inores.html (524 words)

	Course Descriptions - Chem 421 (Site not responding. Last check: 2007-10-18)
		This course concentrates on organo-transition metal chemistry, with emphasis on bonding theories, the 18-electron rule and cluster compounds., Emphasis is also placed on the role of organometallic complexes in organic syntheses.
		The experiments performed in the laboratory component of the course will be directly related to the topics discussed during lectures.
		The isolobal concept; the 16/18-electron rule and its exceptions;
	www.ucfv.bc.ca /__shared/printpages/page1224.htm (127 words)

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