The Microscopic or Particulate Perspective

The particulate perspective provides a more detailed look at the distinction between chemical and physical changes. Because atoms and molecules are far too small to observe directly or to photograph, typically we will use simplified, schematic drawings to depict them in this book. Often, atoms and molecules will be drawn as circles to depict them and consider their changes. 

The word atom comes from the Creek word atomos meaning indivisible. 

To correctly depict the relative densities of a gas and a liquid, much more space would need to be shown between particles in a gas than can be shown in a drawing like Rgpre 1.3. 

If we observe these two reactions macroscopically, what would we see and how would we know the difference In both cases, we would see bubbles forming, only in one case the bubbles will contain water vapor (gas) and in the other they contain hydrogen. Despite this similarity, we can make observations at the macroscopic level to distinguish between these two possibilities. Example Problem 1.1 poses an experiment that could be set up to make such observation. 

Consider the experimental apparatus shown in the photo to the right. This equipment could be used to test a hypothesis about the chemical composition of the gas in the bubbles that rise from boiling water. What would the observation be if the bubbles were composed of (a) water, (b) hydrogen, or (c) oxygen  

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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. 

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