Lewis structure octet-based

Lewis structures are drawn to represent the arrangement of the valence electrons in a molecule. The rules for drawing Lewis structures are based on the observation that nonmetal atoms tend to achieve noble gas electron configurations by sharing electrons. This leads to a duet rule for hydrogen and to an octet rule for many other atoms. 

Now we will apply this formal-charge concept to the cyanate ion OCN We chose this example because many students incorrectly write the formula as CNO , and then try to use this as the atomic arrangement in the Lewis structure. Based on the number of electrons needed, the carbon should be the central atom. We will work this example using both the incorrect atom arrangement and the correct atom arrangement. Notice that in both structures all atoms have a complete octet. 

The atoms that obey the octet rule are O in BeO, F in NF, and O in Oj. Keep in mind that this is only based on the Lewis structures, not on the results of more accurate MO theory,... 

For some molecules or polyatomic ions, two or more Lewis shuctures based on the same skeletal structure satisfy the octet rule and appear chemically reasonable. Taken together, such resonance structures represent the molecule or ion more accurately than any single Lewis structure does. 

An ylide is a neutral species whose Lewis structure contains opposite charges on adjacent atoms. The atoms involved are carbon and an element from either group 15 (VA) or 16 (VIA) of the periodic table, such as N, P, or S. The Wittig reaction uses phosphorus ylides, which are obtained by deprotonation of a phosphonium salt with a strong base. Phosphorus ylides are relatively stable, but reactive species, for which the following resonance structures may be written the phosphorus atom can exceed an octet by accommodating electron donation into its 3d orbitals. 

In 1923. Lewis published a classic book (later reprinted by Dover Publications) titled Valence and the Structure of Atoms and Molecules. Here, in Lewis s characteristically lucid style, we find many of the basic principles of covalent bonding discussed in this chapter. Included are electron-dot structures, the octet rule, and the concept of electronegativity. Here too is the Lewis definition of acids and bases (Chapter 15). That same year, Lewis published with Merle Randall a text called Thermodynamics and the Free Energy of Chemical Substances. Today, a revised edition of that text is still used in graduate courses in chemistry. 

It must be emphasized that the duodectet rule (4.6) initially has no structural connotation, but is based on composition only. Indeed, the compositional regularity expressed by (4.6) encompasses both molecular species (such as the metal alkyls) and extended lattices (such as the oxides and halides) and therefore appears to transcend important structural classifications. Nevertheless, we expect (following Lewis) that such a rule of 12 may be associated with specific electronic configurations, bond connectivities, and geometrical propensities (perhaps quite different from those of octet-rule-conforming main-group atoms) that provide a useful qualitative model of the chemical and structural properties of transition metals. 

The octet rate allows chemists to predict the place-mart of electrons around the nucleus (electroi orbitals), the identification of electrons added or lost during chemical reaofions, and the chemical reactivity of atoms based upon their particular electron configuration. The octet rale is used when drawing Lewis dot structures and diagraming electron configurations. 

Nitrogen is a gas under standard contitions as can be expected from the final structure non-poiar, low- molocular. weight molecule. It is also diamagnetic as can be expected from the fact that all electrons are paired with an octet. N2 could also react as a Lewis base each N atom still has a lone electron pair, but it is likely to be a weak one due to the fact that N atoms have high electronegativity and the electrons have low energy. N2 is also a very unreactive gas as can be expected from a triple bond between its atoms. 

The Lewis (1916) theory of valence may be considered as the first serious attempt to account for both polar and nonpolar bonds and, consequently, to describe the electronic structure of any chemical species. This theory is based on the famous octet rule, which may be stated as every atom tends to acquire eight electrons in its outer shell, those being normally arranged in pairs at the four corners of a tetrahedron. Moreover, assuming the interpenetrability of atomic shells, Lewis shows that, in a nonpolar compound, each atom can satisfy the octet rule by sharing one or more electron pairs with the neighboring atom(s). This pairing of elec-... 

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