Overhead Projector Spectrum of Polymethine Dye: A Physical Chemistry Demonstration

Chemical bond plays a central role in the description of the physicochemical properties of molecules and solids and it is essential to several fields in science and engineering, governing the material’s mechanical, electrical, catalytic and optoelectronic properties, among others. Due to this indisputable importance, a proper description of chemical bond is needed, commonly obtained through solving the Schrödinger equation of the system with either molecular orbital theory (molecules) or band theory (solids). However, connecting these seemingly different concepts is not a straightforward task for students and there is a gap in the available textbooks concerning this subject. This work presents a chemical content to be added in the physical chemistry undergraduate courses, in which the framework of molecular orbitals was used to qualitatively explain the standard state of the chemical elements and some properties of the resulting material, such as gas or crystalline solids. Here in Part 1, we were able to show the transition from Van der Waals clusters to metal in alkali and alkaline earth systems. In Part 2 and 3 of this three-part work, the present framework is applied to main group elements and transition metals. The original content discussed here can be adapted and incorporated in undergraduate and graduate physical chemistry and/or materials science textbooks and also serves as a conceptual guide to subsequent disciplines such as quantum chemistry, quantum mechanics and solid-state physics.

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A Master Class in Dimensional Analysis: the Universal Gas Constant

10.26434/chemrxiv.6874886.v1 ◽

2018 ◽

Author(s):

john andraos

Keyword(s):

Physical Chemistry ◽

High School ◽

General Chemistry ◽

Dimensional Analysis ◽

Undergraduate Students ◽

Microsoft Excel ◽

Energy Unit ◽

Spreadsheet Program ◽

Volume Unit

We present a spreadsheet-assisted exercise using Microsoft Excel software for the determination of the universal gas constant, R, in 35,712 different units. This large number of units arises from a simple enumeration of possible pressure-volume unit combinations and energy unit combinations covering SI (metric), Imperial (British), and American units. In turn, various units for force and area used for defining pressure, and various units for force and distance used for defining energy are explored. This presentation serves as an excellent exercise for high school and undergraduate students to master the skill of dimensional analysis, unit conversions, and basic combinatorics in general chemistry and physical chemistry courses. Instructors can also use the described exercise of constructing conversion matrices to train students in how to efficiently use the Microsoft Excel spreadsheet program.

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