General Concepts for Covalent Bonding and Constructing Lewis Structures for Organic Molecules

Two-dimensional cuts through spin-integrated single-particle density matrices (SPDMs) have proven to be a valuable tool to discuss the nature of chemical bonding independent of the degree of rotation of the underlying orbitals in Hilbert space. Starting from a straightforward concept for the interpretation of σ bonds, we briefly present how the transition from purely ionic to mainly covalent bonding is mirrored in the off-diagonal features of the SPDM in the isoelectronic series LiF, BeO and BN. Furthermore, we outline one of several possible ways to extend the graphical representation and interpretation of SPDMs to the case of π bonds in organic molecules and apply it to the conjugated π-electron system 1,6-hexadiynediol.

Download Full-text

The Role of Lewis Structures in Teaching Covalent Bonding

Journal of Chemical Education ◽

10.1021/ed078p1457 ◽

2001 ◽

Vol 78 (11) ◽

pp. 1457 ◽

Cited By ~ 2

Author(s):

S. R. Logan

Keyword(s):

Covalent Bonding ◽

Lewis Structures

Download Full-text

Conceptual integration of covalent bond models by Algerian students

Chemistry Education Research and Practice ◽

10.1039/c4rp00041b ◽

2014 ◽

Vol 15 (4) ◽

pp. 675-688 ◽

Cited By ~ 1

Author(s):

Hazzi Salah ◽

Alain Dumon

Keyword(s):

Covalent Bond ◽

Covalent Bonding ◽

Quantum Model ◽

Covalent Bonds ◽

Conceptual Integration ◽

Knowledge Framework ◽

Chemistry Learning ◽

Valence Electrons ◽

Lewis Structures ◽

Hybrid Orbitals

The concept of covalent bonding is characterized by an interconnected knowledge framework based on Lewis and quantum models of atoms and molecules. Several research studies have shown that students at all levels of chemistry learning find the quantum model to be one of the most difficult subjects to understand. We have tried in this paper to analyze the extent to which Algerian students, at the end of their training, have integrated the covalent bonding theories based on the quantum model of atom theory and are able to interpret Lewis structures using the quantum model. The analysis of the responses to a written questionnaire showed that this integration was not achieved by our students and that they are not able to correctly describe covalent bonds in a Lewis structure using the concepts of the quantum model. They have a “quantum box” conception of atomic or hybrid orbitals. This conception acts as a “pedagogical learning impediment” to the integration of the geometrical representations of atomic and hybrid orbitals, the conditions of their overlapping to give bonds and consequently the description of covalent bonds using the quantum model. So, the students use an alternative conceptual framework based on the use of Lewis model paired valence electrons to form covalent bonds that we have named the: “electrons pair framework”. Furthermore, the students restricted the denomination of a covalent bond to the sharing of one electron (either s or p but not spn) from each atom to give one “electron pair σ”, and thought that σ bonds are only formed in single bonds.

Download Full-text

High Resolution Replication of Organoclay Surfaces

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100055126 ◽

1982 ◽

Vol 40 ◽

pp. 576-577

Author(s):

W. W. Barker ◽

W. E. Rigsby ◽

V. J. Hurst ◽

W. J. Humphreys

Keyword(s):

Clay Mineral ◽

Organic Molecule ◽

Organic Molecules ◽

X Ray Diffraction ◽

Xrd Pattern ◽

X Ray ◽

Naturally Occurring ◽

Silicate Layers ◽

Mineral Identification

Experimental clay mineral-organic molecule complexes long have been known and some of them have been extensively studied by X-ray diffraction methods. The organic molecules are adsorbed onto the surfaces of the clay minerals, or intercalated between the silicate layers. Natural organo-clays also are widely recognized but generally have not been well characterized. Widely used techniques for clay mineral identification involve treatment of the sample with H2 O2 or other oxidant to destroy any associated organics. This generally simplifies and intensifies the XRD pattern of the clay residue, but helps little with the characterization of the original organoclay. Adequate techniques for the direct observation of synthetic and naturally occurring organoclays are yet to be developed.

Download Full-text

Direct phase determination in electron crystallography: small organic molecules

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100130468 ◽

1992 ◽

Vol 50 (2) ◽

pp. 1166-1167

Author(s):

Douglas L. Dorset

Keyword(s):

Organic Molecules ◽

Data Sets ◽

Temperature Structure ◽

3D Analysis ◽

Intensity Data ◽

Electron Crystallography ◽

Phase Determination ◽

Measured Intensity ◽

3D Data

The quantitative use of electron diffraction intensity data for the determination of crystal structures represents the pioneering achievement in the electron crystallography of organic molecules, an effort largely begun by B. K. Vainshtein and his co-workers. However, despite numerous representative structure analyses yielding results consistent with X-ray determination, this entire effort was viewed with considerable mistrust by many crystallographers. This was no doubt due to the rather high crystallographic R-factors reported for some structures and, more importantly, the failure to convince many skeptics that the measured intensity data were adequate for ab initio structure determinations.We have recently demonstrated the utility of these data sets for structure analyses by direct phase determination based on the probabilistic estimate of three- and four-phase structure invariant sums. Examples include the structure of diketopiperazine using Vainshtein's 3D data, a similar 3D analysis of the room temperature structure of thiourea, and a zonal determination of the urea structure, the latter also based on data collected by the Moscow group.

Download Full-text