Electronic formula

Hume-Rothery s rule The statement that the phase of many alloys is determined by the ratio.s of total valency electrons to the number of atoms in the empirical formula. See electron compounds. 

Note. The maximum number of electrons that any quantum level can accommodate is seen to be given by the formula 2n where n is the number of the quantum level, for example = 3 the maximum number of electrons is therefore 18. 

Reference has already been made to the high melting point, boiling point and strength of transition metals, and this has been attributed to high valency electron-atom ratios. Transition metals quite readily form alloys with each other, and with non-transition metals in some of these alloys, definite intermetallic compounds appear (for example CuZn, CoZn3, Cu3,Sng, Ag5Al3) and in these the formulae correspond to certain definite electron-atom ratios. 

Cobalt has an odd number of electrons, and does not form a simple carbonyl in oxidation state 0. However, carbonyls of formulae Co2(CO)g, Co4(CO)i2 and CoJCO),6 are known reduction of these by an alkali metal dissolved in liquid ammonia (p. 126) gives the ion [Co(CO)4] ". Both Co2(CO)g and [Co(CO)4]" are important as catalysts for organic syntheses. In the so-called oxo reaction, where an alkene reacts with carbon monoxide and hydrogen, under pressure, to give an aldehyde, dicobalt octacarbonyl is used as catalyst ... 

Factual databases may provide the electronic version of printed catalogs on chemical compoimds. The catalogs of different suppliers of chemicals serve to identify chemical compounds with their appropriate synonyms, molecular formulas, molecular weight, structure diagrams, and - of course - the price. Sometimes the data are linked to other databases that contain additional information. Structure and substructure search possibihties have now been included in most of the databases of chemical suppliers. 

Lee C, W Yang and R G Parr 1988. Development of the Colle-Salvetti Correlation Energy Formula into a Functional of the Electron Density. Physical Review B37 785-789. 

The trends in chemical and physical properties of the elements described beautifully in the periodic table and the ability of early spectroscopists to fit atomic line spectra by simple mathematical formulas and to interpret atomic electronic states in terms of empirical quantum numbers provide compelling evidence that some relatively simple framework must exist for understanding the electronic structures of all atoms. The great predictive power of the concept of atomic valence further suggests that molecular electronic structure should be understandable in terms of those of the constituent atoms. 

Relativistic density functional theory can be used for all electron calculations. Relativistic DFT can be formulated using the Pauli formula or the zero-order regular approximation (ZORA). ZORA calculations include only the zero-order term in a power series expansion of the Dirac equation. ZORA is generally regarded as the superior method. The Pauli method is known to be unreliable for very heavy elements, such as actinides. 

Most of the qualitative relationships between color and structure of methine dyes based on the resonance theory were established independently during the 1940 s by Brooker and coworkers (16, 72-74) and by Kiprianov (75-78), and specific application to thiazolo dyes appeared later with the studies of Knott (79) and Rout (80-84). In this approach, the absorptions of dyes belonging to amidinium ionic system are conveyed by a group of contributing structures resulting from the different ways of localization of the 2n rr electrons on the 2n l atoms of the chromophoric cationic chain, rather than by a single formula ... 

Structural formulas of this type in which electrons are represented as dots are called Lewis structures... 

Organic chemists have devised a number of shortcuts to speed the writing of structural formulas Sometimes we leave out unshared electron pairs but only when we are sure enough m our ability to count electrons to know when they are present and when they re not We ve already mentioned representing covalent bonds by dashes In condensed structural formulas we leave out some many or all of the covalent bonds and use sub scripts to indicate the number of identical groups attached to a particular atom These successive levels of simplification are illustrated as shown for isopropyl alcohol ( rub bmg alcohol )... 

Structural formula J is a Lewis structure of nitro methane K is not even though it has the same atomic positions and the same number of electrons... 

So far we have emphasized structure in terms of electron bookkeeping We now turn our attention to molecular geometry and will see how we can begin to connect the three dimensional shape of a molecule to its Lewis formula Table 1 6 lists some simple com pounds illustrating the geometries that will be seen most often m our study of organic chemistry... 

Compound Structural Formula Repulsive Electron Pairs of Electron Pairs Molecular Shape Molecular Model... 

The same G N Lewis who gave us electron dot formulas also suggested a way of think mg about acids and bases that is more general than the Brpnsted-Lowry approach Where Brpnsted and Lowry viewed acids and bases as donors and acceptors of protons (positively charged) Lewis took the opposite view and focused on electron pairs (negatively charged) According to Lewis an acid is an electron pair acceptor and a base is an electron pair donor... 

Orbital hybridization descriptions because they too are based on the shared electron pair bond enhance the information content of Lewis formulas by distinguishing... 

Electron delocalization m allylic carbocations can be indicated using a dashed line to show the sharing of a pair of rr electrons by the three carbons The structural formula IS completed by placing a positive charge above the dashed line or by adding partial pos itive charges to the carbons at the end of the allylic system... 

The circle m a hexagon symbol was first suggested by the British chemist Sir Robert Robinson to represent what he called the aromatic sextet —the six delocalized TT electrons of the three double bonds Robinson s symbol is a convenient time saving shorthand device but Kekule type formulas are better for counting and keeping track of electrons especially m chemical reactions... 

Ultraviolet visible (UV VIS) spectroscopy, which probes the electron distribution especially m molecules that have conjugated n electron systems Mass spectrometry (MS), which gives the molecular weight and formula both of the molecule itself and various structural units within it... 

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