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

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.Peer reviewe

Restraining fluoride loss from NaYF4:Yb3+,Er3+ upconverting nanoparticles in aqueous environments using crosslinked poly(acrylic acid)/poly(allylamine hydrochloride) multilayers

The use of upconverting nanoparticles in various applications in aqueous media relies on their surface modifications as most synthesis routes yield hydrophobic particles. However, introducing upconverting nanoparticles in aqueous solutions commonly results in the quenching of their luminescence intensity and in the worst case, disintegration of the nanoparticles. We demonstrate the use of poly(acrylic acid) and poly(allylamine hydrochloride) as a protecting layer-by-layer coating for the upconverting NaYF4:Yb3+,Er3+ nanoparticles. The formation and crosslinking of the bilayer coating was confirmed with Fourier transform infrared spectroscopy, thermal analysis and zeta potential. The release of internal fluoride ions from the nanoparticle structure and subsequent particle disintegration was decelerated especially by crosslinking the bilayer coating on the surface. In addition, we studied the effect of the coating on the upconversion luminescence properties and learned that with additional fluoride ions present during the layer-by-layer assembly the most intense enhancement in the luminescent intensity is obtained. This is due both to not allowing the disintegration of the particles during the surface modification process as well as preventing the water molecules accessing the surface by crosslinking the bilayer coating.</p

Highly controllable ambient atmosphere spray deposition of water dispersible poly(benzimidazobenzophenanthroline) films

Thin films of water dispersible poly(ethylene oxide) (PEO) functionalized poly(benzimidazobenzophenanthroline) (BBL) polymers have been prepared by a pulse spray technique on a spinning substrate in ambient atmosphere. The deposition method is advantageous for generating ultra-thin films of nanometer thicknesses. A single spray pulse was found in a reproducible manner to generate a layer of ca. 2 nm thickness. The PEO-chain length in the BBL functionalization had an essential influence on the building mechanism of the films. The polymers functionalized by short PEO chains induced the formation of very smooth films while longer PEO chains induced rough films and notable nanostructuration. The BBL-PEO film deposited using spray pulse deposition was found to be electro- and photoactive. The electron transfer processes observed are slightly different from earlier reported results for similar polymers, which is probably due to the very thin film. The films exhibited photocurrent generation when transformed into conducting form.Peer reviewe

Heuristics hindering the development of understanding of molecular structures in university level chemistry education: The lewis structure as an example

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.</p

Effects of pH and Oxidants on the First Steps of Polydopamine Formation: A Thermodynamic Approach

We present a general thermodynamic top-down analysis of the effects of oxidants and pH on dopamine oxidation and cyclization, supplemented with UV-vis and electrochemical studies. The model is applicable to other catecholamines and various experimental conditions. The results show that the decisive physicochemical parameters in autoxidation are the pK values of the semiquinone and the amino group in the oxidized quinone. Addition of Ce(IV) or Fe(III) enhances dopamine oxidation in acidic media in aerobic and anaerobic conditions by the direct oxidation of dopamine and, in the presence of oxygen, also by the autoxidation of the formed semiquinone. At pH 4.5, the enhancement of the one-electron oxidation of dopamine explains the overall reaction enhancement, but at a lower pH, cyclization becomes rate-determining. Oxidation by Cu(II) at reasonable rates requires the presence of oxygen or chloride ions

Synthesis of Layered Double Hydroxides and TiO2 Supported Metal Nanoparticles for Electrocatalysis

In the present work, solution-phase synthesis was employed to prepare two sets of catalysts with different transition metals as active sites. One set contained Au or Pd supported on TiO2 (Au-TiO2, Pd-TiO2), whereas the other set contained layered double hydroxides (NiFe-LDH and CuFe-LDH). The electrocatalytic performance of these composite materials was investigated by cyclic voltammetry (CV) using a model compound 4-nitrophenol (4-NP). Composite materials were characterized by various analytical techniques to gain insight into the catalysts active sites. The morphology and structure of the prepared samples were investigated by X-ray diffraction, attenuated total reflectance Fourier transform infrared, X-ray photoelectron spectroscopy, transmission scanning electron microscope, and field emission scanning electron microscope. Metal nanoparticles loading on TiO2 was measured by inductively coupled plasma - optical emission spectrometry. CV measurements were performed in acetonitrile solution containing 0.1 m tetrabutylammonium hexafluorophosphate (TBAPF(6)) and 1 mm 4-NP. Among all dioxides (Au-TiO2, Pd-TiO2) and hydroxides (NiFe-LDH and CuFe-LDH) studied, Pd-TiO2 shows the lowest onset potential (-0.32 V vs. Ag/AgCl) for the electrocatalytic reduction of 4-NP. This is the first comparative study of such materials for 4-NP electrocatalysis in aprotic solvent, thus demonstrating the suitability of dioxide and hydroxide based materials as electrocatalysts

Effect of Water on a Hydrophobic Deep Eutectic Solvent

Deep eutectic solvents (DESs) formed by hydrogen bond donors and acceptors are a promising new class of solvents. Both hydrophilic and hydrophobic binary DESs readily absorb water, making them ternary mixtures, and a small water content is always inevitable under ambient conditions. We present a thorough study of a typical hydrophobic DES formed by a 1:2 mole ratio of tetrabutyl ammonium chloride and decanoic acid, focusing on the effects of a low water content caused by absorbed water vapor, using multinuclear NMR techniques, molecular modeling, and several other physicochemical techniques. Already very low water contents cause dynamic nanoscale phase segregation, reduce solvent viscosity and fragility, increase self-diffusion coefficients and conductivity, and enhance local dynamics. Water interferes with the hydrogen-bonding network between the chloride ions and carboxylic acid groups by solvating them, which enhances carboxylic acid self-correlation and ion pair formation between tetrabutyl ammonium and chloride. Simulations show that the component molar ratio can be varied, with an effect on the internal structure. The water-induced changes in the physical properties are beneficial for most prospective applications but water creates an acidic aqueous nanophase with a high halide ion concentration, which may have chemically adverse effects.</p