Lewis structures, formal charge, and oxidation numbers: A more user-friendly approach

1991 ◽  
Vol 68 (6) ◽  
pp. 456 ◽  
Author(s):  
John E. Packer ◽  
Sheila D. Woodgate
Keyword(s):  
Formal Charge ◽  
User Friendly ◽  
Lewis Structures

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.

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 Added Value of Graphical Input and Display for Electron Lens Design

1990 ◽  
Vol 48 (1) ◽  
pp. 190-191
Author(s):  
B. Lencova ◽  
G. Wisselink
Keyword(s):  
Flux Density ◽  
Numerical Data ◽  
Added Value ◽  
Lens Design ◽  
Step Size ◽  
Magnetic Lens ◽  
Flux Lines ◽  
Fine Mesh ◽  
Electron Lens ◽  
User Friendly

Recent progress in computer technology enables the calculation of lens fields and focal properties on commonly available computers such as IBM ATs. If we add to this the use of graphics, we greatly increase the applicability of design programs for electron lenses. Most programs for field computation are based on the finite element method (FEM). They are written in Fortran 77, so that they are easily transferred from PCs to larger machines.The design process has recently been made significantly more user friendly by adding input programs written in Turbo Pascal, which allows a flexible implementation of computer graphics. The input programs have not only menu driven input and modification of numerical data, but also graphics editing of the data. The input programs create files which are subsequently read by the Fortran programs. From the main menu of our magnetic lens design program, further options are chosen by using function keys or numbers. Some options (lens initialization and setting, fine mesh, current densities, etc.) open other menus where computation parameters can be set or numerical data can be entered with the help of a simple line editor. The "draw lens" option enables graphical editing of the mesh - see fig. I. The geometry of the electron lens is specified in terms of coordinates and indices of a coarse quadrilateral mesh. In this mesh, the fine mesh with smoothly changing step size is calculated by an automeshing procedure. The options shown in fig. 1 allow modification of the number of coarse mesh lines, change of coordinates of mesh points or lines, and specification of lens parts. Interactive and graphical modification of the fine mesh can be called from the fine mesh menu. Finally, the lens computation can be called. Our FEM program allows up to 8000 mesh points on an AT computer. Another menu allows the display of computed results stored in output files and graphical display of axial flux density, flux density in magnetic parts, and the flux lines in magnetic lenses - see fig. 2. A series of several lens excitations with user specified or default magnetization curves can be calculated and displayed in one session.

A Review of 21 iPad Applications for Augmentative and Alternative Communication Purposes

2012 ◽  
Vol 21 (2) ◽  
pp. 60-71 ◽  
Author(s):  
Ashley Alliano ◽  
Kimberly Herriger ◽  
Anthony D. Koutsoftas ◽  
Theresa E. Bartolotta
Keyword(s):  
Augmentative And Alternative Communication ◽  
Cost Effective ◽  
Alternative Form ◽  
Alternative Communication ◽  
Text To Speech ◽  
Reference Guide ◽  
Expressive Communication ◽  
Communication Needs ◽  
User Friendly ◽  
Ipad Applications

Abstract Using the iPad tablet for Augmentative and Alternative Communication (AAC) purposes can facilitate many communicative needs, is cost-effective, and is socially acceptable. Many individuals with communication difficulties can use iPad applications (apps) to augment communication, provide an alternative form of communication, or target receptive and expressive language goals. In this paper, we will review a collection of iPad apps that can be used to address a variety of receptive and expressive communication needs. Based on recommendations from Gosnell, Costello, and Shane (2011), we describe the features of 21 apps that can serve as a reference guide for speech-language pathologists. We systematically identified 21 apps that use symbols only, symbols and text-to-speech, and text-to-speech only. We provide descriptions of the purpose of each app, along with the following feature descriptions: speech settings, representation, display, feedback features, rate enhancement, access, motor competencies, and cost. In this review, we describe these apps and how individuals with complex communication needs can use them for a variety of communication purposes and to target a variety of treatment goals. We present information in a user-friendly table format that clinicians can use as a reference guide.

A “User-Friendly” Guide to Therapy With Men

PsycCRITIQUES ◽  
2010 ◽  
Vol 55 (26) ◽  
Author(s):  
Jay C. Wade
Keyword(s):  
User Friendly
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