Which Method of Assigning Bond Orders in Lewis Structures Best Reflects Experimental Data? An Analysis of the Octet Rule and Formal Charge Systems for Period 2 and 3 Nonmetallic Compounds

2009 ◽  
Vol 86 (10) ◽  
pp. 1241 ◽  
Author(s):  
Ronald F. See
Keyword(s):  
Experimental Data ◽  
Bond Orders ◽  
Period 2 ◽  
Formal Charge ◽  
Lewis Structures ◽  
Octet Rule

Chemical Bonding 1: Basic Concepts

2021 ◽  
pp. 81-101
Author(s):  
Christopher O. Oriakhi
Keyword(s):  
Chemical Bonding ◽  
Chemical Properties ◽  
Lattice Energy ◽  
Bond Polarity ◽  
Formal Charge ◽  
Basic Concepts ◽  
Lewis Structures ◽  
The Relationship ◽  
Octet Rule

Chemical Bonding I: Basic Concepts examines general ideas of chemical bonding between atoms and ions and how this bonding affects the chemical properties of the elements. An overview of Lewis symbols, Lewis structures and the octet rule is presented including the role of valence electrons in ionic and covalent bonding. The energy changes that accompany ionic bond formation are also discussed with emphasis on lattice energy. The chapter covers guidelines and general procedures for writing Lewis structures or electron dot formulas for molecular compounds and polyatomic ions. The concepts and applications of resonance, formal charge and exceptions to the octet rules are presented, along with coverage of the relationship between bond polarity and electronegativity.

Toward a comprehensive definition of oxidation state (IUPAC Technical Report)

2014 ◽  
Vol 86 (6) ◽  
pp. 1017-1081 ◽  
Author(s):  
Pavel Karen ◽  
Patrick McArdle ◽  
Josef Takats
Keyword(s):  
Oxidation State ◽  
Structural Formula ◽  
The Other ◽  
Bond Orders ◽  
Formal Charge ◽  
Technical Report ◽  
Electronegative Atom ◽  
Auxiliary Rules ◽  
Definition Of

AbstractA generic definition of oxidation state (OS) is formulated: “The OS of a bonded atom equals its charge after ionic approximation”. In the ionic approximation, the atom that contributes more to the bonding molecular orbital (MO) becomes negative. This sign can also be estimated by comparing Allen electronegativities of the two bonded atoms, but this simplification carries an exception when the more electronegative atom is bonded as a Lewis acid. Two principal algorithms are outlined for OS determination of an atom in a compound; one based on composition, the other on topology. Both provide the same generic OS because both the ionic approximation and structural formula obey rules of stable electron configurations. A sufficiently simple empirical formula yields OS via the algorithm of direct ionic approximation (DIA) by these rules. The topological algorithm works on a Lewis formula (for a molecule) or a bond graph (for an extended solid) and has two variants. One assigns bonding electrons to more electronegative bond partners, the other sums an atom’s formal charge with bond orders (or bond valences) of sign defined by the ionic approximation of each particular bond at the atom. A glossary of terms and auxiliary rules needed for determination of OS are provided, illustrated with examples, and the origins of ambiguous OS values are pointed out. An electrochemical OS is suggested with a nominal value equal to the average OS for atoms of the same element in a moiety that is charged or otherwise electrochemically relevant.

scholarly journals Heuristics Hindering the Development of Understanding of Molecular Structures in University Level Chemistry Education: The Lewis Structure as an Example

2021 ◽  
Vol 11 (6) ◽  
pp. 258
Author(s):  
Maarit Karonen ◽  
Mari Murtonen ◽  
Ilona Södervik ◽  
Marianna Manninen ◽  
Mikko Salomäki
Keyword(s):  
Chemistry Education ◽  
Molecular Structures ◽  
Multiple Choice Questions ◽  
Chemical Models ◽  
Formal Charge ◽  
Post Test ◽  
University Level ◽  
Drawing Tasks ◽  
Systemic Understanding ◽  
Lewis Structures

Understanding chemical models can be challenging for many university students studying chemistry. This study analysed students’ understanding of molecular structures using the Lewis structure as a model, and examined what hinders their understanding. We conducted pre- and post-tests to analyse students’ conceptions and changes in them. The measures contained multiple-choice questions and drawing tasks testing their understanding of concepts, such as polarity, geometry, charge or formal charge and expanded octet. The pre-test revealed a lack of knowledge and several misconceptions in students’ prior knowledge. For example, the concept of polarity was well-known, but the combination of polarity and geometry appeared to be difficult. For some students, the representation of molecules was intuitive and lacking a systematic approach. Certain students used mnemonics and draw ball-and-stick models connected to surficial representations. After the chemistry courses, the conceptions and drawings had generally changed, and the level of the students’ knowledge increased markedly. Although, fewer ball-and-stick models were drawn in the post-test, some students still used them. The main result was that students who drew ball-and-stick models in the pre-test were less capable of drawing the correct Lewis structures with electrons in the post-test. In addition, heuristics seem to hinder learning and some concepts, such as resonance, remained difficult. This is probably due to the fact that understanding molecular structures requires systemic understanding, where several matters must be understood at the same time. Our study highlights that the understanding of molecular structures requires conceptual change related to several sub-concepts.

Valence Bond Studies of N5+

2002 ◽  
Vol 57 (9) ◽  
pp. 983-992 ◽  
Author(s):  
Richard D. Harcourta ◽  
Thomas M. Klapötkeb
Keyword(s):  
Valence Bond ◽  
Molecular Orbital Calculations ◽  
Energy Minimum ◽  
Localized Molecular Orbitals ◽  
Bond Lengths ◽  
Formal Charge ◽  
Valence Structure ◽  
Valence Bond Structure ◽  
Lewis Structures ◽  
Increased Valence

The results of STO-6G valence-bond studies are reported for the six π-electrons of C2v symmetry N5+, with π-electron core charges determined from the valence bond structures. Important types of canonical Lewis structures are calculated to carry either three atomic formal charges, arranged spatially as (+), (-) and (+) , as in or a single (+) atomic formal charge, as in the “long-bond” structure When localized molecular orbitals are used to accommodate bonding electrons between pairs of adjacent atoms, each of these types of Lewis structures, and others, are components of the increased-valence structure whose bond properties are in qualitative accord with experimental estimates of the bond lengths for N5+. Consideration is also given to other types of valence bond representations for N5+, and the results of MP2 molecular orbital calculations for the hypothetical N82+ are reported. For the latter species, a stable energy minimum with C2 symmetry is obtained. Its bond lengths are related to those implied by a Lewis-type valence-bond structure

The Variable Electronegativity Method. VI. Azulene

1960 ◽  
Vol 13 (1) ◽  
pp. 38 ◽  
Author(s):  
RD Brown ◽  
ML Heffernan
Keyword(s):  
Experimental Data ◽  
Magnetic Resonance ◽  
Carbon Atom ◽  
Electron Density ◽  
Proton Magnetic Resonance ◽  
Resonance Spectrum ◽  
Dipole Moments ◽  
Proton Magnetic Resonance Spectrum ◽  
Bond Orders ◽  
Electron Distributions

Results of a variable-electronegativity SCF treatment of azulene, using the method used in previous VESCF studies, are reported. A slightly more elaborate method in which non-neighbour core resonance integrals are included has also been used. The π-electron distributions obtained by these methods correspond to dipole moments of 1.85 and 1.33 D respectively, the experimental value being about 1 D. The calculated bond orders accord with the rather incomplete experimental data on bond lengths. The π-electron densities account for the relative chemical reactivities of the azulene positions. The ionization potentials and proton magnetic resonance spectrum of azulene are also briefly considered. The concept of electronegativities of conjugated atoms in non-alternant systems is discussed in some detail on the basis of the VESCF results. It is shown that the assumption that the electronegativity of a carbon atom depends only on its π-electron density is an oversimplification for non-alternant systems.

N.M.R.-Studies of Bond Order in Azulene, Biphenylene and 1,6-Methano[10]annulene

1990 ◽  
Vol 43 (9) ◽  
pp. 1541 ◽  
Author(s):  
MJ Collins ◽  
S Sternhell ◽  
CW Tansey
Keyword(s):  
Experimental Data ◽  
Ground State ◽  
Bond Order ◽  
Membered Ring ◽  
Coupling Constants ◽  
Bond Orders ◽  
Bond Lengths ◽  
Theoretical Predictions ◽  
Electron Distributions ◽  
Good Agreement

The 4J(H-C-C-Me) coupling constants of methyl-substituted derivatives, probes of bond order, have been used to examine the ground-state π- electron distributions in azulene (1), biphenylene (2) and 1,6- methano [10] annulene (3). The experimental data obtained are in good agreement with theoretical predictions for biphenylene (2) and provide some evidence for π-electron disproportionation towards the five-membered ring in azulene (1). The bond orders in 1,6-methano [10] annulene (3) obtained in this work are at variance with those predicted on the grounds of bond lengths.

LCAO MO CALCULATIONS ON A SERIES OF NITRILES AND SOME RELATED MOLECULES BY A METHOD OF SELF-CONSISTENT FORMAL CHARGES

1964 ◽  
Vol 42 (6) ◽  
pp. 1323-1332 ◽  
Author(s):  
J. B. Moffat
Keyword(s):  
Experimental Data ◽  
Input Data ◽  
Electron Systems ◽  
Bond Orders ◽  
Mo Calculations ◽  
Bond Lengths ◽  
Triple Bonds ◽  
Self Consistent ◽  
Good Agreement ◽  
Lcao Mo

A method of self-consistent charges has been applied to an LCAO MO calculation of a series of nitriles and some related molecules. The π-electron bond orders and π-electron densities were calculated for all the molecules considered. The entire calculation was programmed for operation on the IBM 1620 with alterations of the input data for the different molecules. The calculated bond orders yield bond lengths for C—C and C=C bonds in good agreement with experimental data, except when two or more triple bonds are present in the molecule. By the assumption of additivity of the bond orders obtained for the two orthogonal pi-electron systems, bond orders are obtained which yield bond lengths in satisfactory agreement with the experimental results for all CC bonds. For the nitrile bonds the calculated bond orders were fitted to a linear equation with the experimental bond lengths.

Microdiffraction Patterns of Small Metallic Particles II; Theoretical Analysis

1982 ◽  
Vol 40 ◽  
pp. 668-669
Author(s):  
A. Gómez ◽  
P. Schabes-Retchkiman ◽  
M. José-Yacamán ◽  
T. Ocaña
Keyword(s):  
Experimental Data ◽  
Electron Diffraction ◽  
Theoretical Analysis ◽  
Size Range ◽  
Dynamical Theory ◽  
Metallic Particles ◽  
Splitting Effect

The splitting effect that is observed in microdiffraction pat-terns of small metallic particles in the size range 50-500 Å can be understood using the dynamical theory of electron diffraction for the case of a crystal containing a finite wedge. For the experimental data we refer to part I of this work in these proceedings.

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