The formation and reductive desorption of self-assembled monolayers of 6-mercaptohexanol on mercury has been studied by using cathodic stripping voltammetry and capacitative transients, including the possibility of expanding or contracting the electrode area at the end of the preconcentration step. Experimental evidence shows the existence of three sequential stages during the formation of a thiol self-assembled monolayer. Each of these stages can be associated to the presence of (i) a low surface density state of oxidized thiol molecules, characterized by a single electrodimerization wave, (ii) a high surface density state, characterized by the emergence of a second voltammetric wave, and (iii) an ordered monolayer, which gives rise to a voltammetric spike. On the basis of electrode expansion experiments, a method is described to determine the surface concentrations of oxidized products, which does not require a baseline subtraction of the voltammograms to account for the nonfaradaic current. Quantitative voltammetric fits are consistent with the initial formation of a mixture of noninteracting monomers and dimers of oxidized thiol. The value of the maximum surface concentration and the ability to block the Ru(NH 3 ) 6 3+ electron transfer reveal that oxidized thiol molecules adopt a nearly perpendicular orientation in the high surface density state, which hampers ionic permeation. A theoretical model is proposed to account for the observed voltammetric behavior. The transition from the lower to the higher surface density states is modeled as a chemical step involving the exchange of metal free sites. Capacitative transients are also interpreted in terms of the three-stages model.

The study reported here was conducted to investigate the perceptions of high school students on the use of educational games as a tool for teaching the periodic table of elements in a chemistry class in Spain. The 127 students who participated in this study came from six different classes in grade 10 (15−16 years old). The students' perceptions of the usefulness of a series of 13 specifically designed games as educational tools was assessed. This was achieved in a survey containing 13 items using a 5point Likert-type scale, which was completed by the students at the end of the unit. The results of the study reveal that the students who participated had positive perceptions regarding the use of educational games. Students usually found the educational games to be an interesting tool to make the learning process more enjoyable. It can be observed that the students' perceptions of the games are more favorable than for other class tasks used in the control group. The opinions indicate that games also stimulated their participation in classroom activities. Moreover, educational games are considered to help students better understand some of the main concepts presented and discussed throughout the unit.

No abstract

No abstract

An easy, cheap and green synthetic route, using high-power ultrasounds and sodium citrate dihydrate as non-toxic reducing and stabilizer agent, produces gold nanoparticles in aqueous solution, and at ambient conditions. The time required for the synthesis is 5.5 min. The spherical nanoparticles obtained by this route show a homogeneous size distribution, within the range 5-17 nm, with an average diameter of 10±1 nm. Moreover, 90% of the particles have a diameter ranging from 7 to 13 nm, and their half-life is more than 30 days. The gold nanoparticles synthesized following this route are known as sononanoparticles. Gold sononanoparticles have been characterized by TEM and XRD and their stability has been studied by UV-Vis spectroscopy. Alternative experimental designs are compared to optimize the proposed synthesis procedure.