Chemistry macroscopic perspective

Observations of the composition and behavior of matter are based on a macroscopic view. Matter that is large enough to be seen is called macroscopic, so all of your observations in chemistry, and everywhere else, start from this perspective. The macroscopic world is the one you touch, feel, smell, taste, and see. The properties of iron shown in Figure 1.3 are seen from a macroscopic perspective. But if you want to describe and understand the structure of iron, you must use a different perspective—one that allows you to see what can t be seen. What you can see of the New York City World Trade Center, shown in Figure 1.5, is similar to a macroscopic perspective. The actual structure of the building is hidden from view. 

The Study of Chemistry The Macroscopic Perspective The Microscopic or Particulate... 

This coherent picture involves three levels of understanding or perspectives on the nature of chemistry macroscopic, microscopic, and symbolic. By the end of this course, you should be able to switch among these perspectives to look at problems involving chemistry in several ways. The things we can see about substances and their reactions provide the macroscopic perspective. We need to interpret these events considering the microscopic (or particulate ) perspective, where we focus on the smallest components of the system. Finally, we need to be able to communicate these concepts efficiendy, so chemists have devised a symbolic perspective that allows us to do that. We can look at these three aspects of chemistry first, to provide a reference for framing our studies at the outset. 

Such achievements have been made possible because of the substantial progresses obtained in other areas of chemistry and physics—particularly concerning the synthesis and characterization of complex chemical systems, and the study of surfaces and interfaces. In this perspective, electrochemistry is a very powerful tool not only for characterizing a supramolecular system, but also for operating the device. Indeed, molecular devices, as their macroscopic counterparts, need energy to operate and signals to communicate with the operator. Electrochemistry can be an interesting... 

In your study of chemistry, you will use both macroscopic and submicroscopic perspectives. For example, sucrose and aspirin are both composed of carbon, hydrogen, and oxygen atoms, but they have different behaviors and functions. These differences must come about because of differences in the submicroscopic arrangement of their atoms. Figure 1.7 shows models that reveal these submicroscopic differences. 

James G. Anderson is Philip S. Weld Professor of Atmospheric Chemistry at Harvard University. He received his B.S. in physics from the University of Washington and his Ph.D. in physics-astrogeophysics from the University of Colorado. His research addresses three domains within physical chemistry (1) chemical reactivity viewed from the microscopic perspective of electron structure, molecular orbitals, and reactivities of radical-radical and radical-molecule systems (2) chemical catalysis sustained by free-radical chain reactions that dictate the macroscopic rate of chemical transformation in the Earth s stratosphere and troposphere and (3) mechanistic links between chemistry, radiation, and dynamics in the atmosphere that control climate. Studies are carried out both in the laboratory, where elementary processes can be isolated, and within natural systems, in which reaction networks and transport patterns are dissected by establishing cause and effect using simultaneous, in situ detection of free radicals, reactive intermediates, and long-lived tracers. Professor Anderson is a member of the National Academy of Sciences. 

Multi-Focus Graphics To help you develop a more complete understanding of the topic presented, Multi-Focus Graphics provide macroscopic, microscopic, and symbolic perspectives to portray various chemical concepts. The Twelfth Edition adds to these graphics an intermediate process that shows you where chemistry is occurring in problem solving, xxxvi... 

A molecular perspective of reactions from quantum chemistry calculations is the first step toward a theoretical design of new electrodes (e.g. binary or even ternary alloys). While reaction mechanisms on Pt and Pt alloy surfaces are getting clearer, details of these mechanism still remain elusive. For example, bifunctional mechanism of CO oxidation on PtSn and PtMo has received very little theoretical attention. Loading effects (CO, OH or specifically adsorbed anions) on CO oxidation is also poorly understood and requires further investigation. Theoretical calculations are also required to understand catalyst reorganization. Details of these calculations are required for accurately modeling the macroscopic kinetics on well-defined electrode surfaces and ultimately designing nanocatalyst particles. 

The inteiiectuai power of chemistry often iies in the way it aiiows us to iook at a probiem (or a design) from a number of perspectives. Both the physicai and chemicai properties of substances can be considered at the macroscopic or microscopic (particuiate) ievei depending on the nature of the question or probiem being considered. In addition, we often need to use symbolic representations to designate what is happening in chemical systems, so ultimately there are three perspectives that we will find useful throughout this text. 

In many ways, the essence of chemistry is considering things on the atomic and molecular level. This idea applies when we study chemical reactions and also when we examine the properties of matter. So as we begin to look at matter and materials from a chemist s perspective, we will always want to focus on the way the properties of matter are related to the properties and behavior of its constituent molecules. Gases provide an excellent starting point for this because the observable macroscopic properties of gases are very direct results of the behavior of individual molecules within the gas. 

As in the case of other material systems, the macroscopic properties of nanocomposites are driven by their micro-/nanoscopic structure. From an electrical insulation perspective, polyethylene (PE) and epoxy resins constitute two technologically important material systems, each of which embodies in very different ways, a great deal of structural complexity. In the case of PE, the constituent molecules are the result of the inherently statistical polymerisation process, which can ultimately result in the formation of a hierarchical morphology in which different molecular fractions become segregated to specific morphological locations. In an epoxy resin, the epoxy monomer chemistry, the hardener and the stoichiometry can all be varied, to affect the network structure that evolves. In the case of nanocomposites, another layer of structural hierarchy is then overlaid upon and interacts with the inherent characteristics of the host matrix. 

In Chapter 10, we treated intermolecular interactions in a series of examples, two particles at a time. As we expand our perspective from the microscopic view of individual molecules out toward the macroscopic limit, we rapidly reach a point where the particles are too numerous to treat their interactions with that same attention to detail. But this point is critical to our understanding of chemistry, because here is also where we first begin to glimpse the properties of bulk materials. 

Statistics will help us reduce the number of coordinates we follow. However, we must not forget the lessons of the molecular perspective. The potential energy function between two molecules is just as important when there are 10 molecules as when there are only two, because every pair of molecules will experience this same potential energy function. The goal of Physical Chemistry Thermodynamics, Kinetics, and Statistical Mechanics is to develop these methods and apply them to obtain the common laws of chemistry that describe how the macroscopic properties of matter are influenced by its microscopic structure. 

The corresponding atomistic kinetics is then implemented into the nonequilibrium nanoscale MEMEPhys models collecting all the elementary events, catalytic and no-catalytic, to simulate the electrochemical observables. The nanoscale models introduce the electric field effect correction without empirical parameters and open interesting perspectives to scale up atomistic data into macroscopic models in a robust way. The impact of the catalyst chemistry and nanostructure on the electrodes and cell potentials can be then captured. 

With Chemistry A Molecular Approach, Tro introduced his revolutionary multipart images that include macroscopic, molecular, and symbolic perspectives with the goal of connecting you to what you see and experience (the macroscopic world) with the molecules responsible for that world (molecular) and with the way chemists represent those molecules (symbolic). This is, after all, what chemistry is all about. 

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