Macroscopic Methods for Classifying Matter

Can it be decomposed into simpler substances by chemical processes  

FIGURE 1.4 (a) A solid mixture of blue Cu(N03)2 6FI2O and yellow CdS is added to water, (b) Although the Cu(N03)2 6FI2O dissolves readily and passes through the filter, the CdS remains largely undlssolved and is held on the filter, (c) Evaporation of the solution leaves nearly pure crystals of Cu(N03)2 6FI2O. 

If all these physical procedures (and many more) fail to separate matter into portions that have different properties, the material is said to be a substance. What about the common material sodium chloride, which we call table salt Is it a substance The answer is yes if we use the term sodium chloride, but no if we use the 

FIGURE 1.5 Nearly pure elemental silicon is produced by pulling a 10-inch-long solid cylinder (called a boule) out of the melt, leaving most of the impurities behind. 

In practice, nothing is absolutely pure, so the word substance is an idealization. Among the purest materials ever prepared are silicon (Fig. 1.5) and germa-ninm. These elements are used in electronic devices and solar cells, and their electronic properties require either high purity or else precisely controlled concentrations of deliberately added impurities. Meticulous chemical and physical methods have enabled scientists to prepare germanium and silicon with concentrations less than one part per billion of impurities. Anything more would alter their electrical properties. 

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