The Nature of Modern Chemistry

3 Indirect Evidence for the Existence of Atoms Laws of Chemical Combination 

Chemists study the properties of substances, their aim being to understand that reactions can transform substances into still other substances. Chemistry thns provides ways to tailor the properties of existing snbstances to meet a particnlar need—and even to create entirely new materials designed to have specific properties. This is how chemistry has improved agricnltnral prodnction, helped prevent and cure many diseases, increased the efficiency of energy production, and rednced environmental pollntion, to cite just a few advances. A particularly exciting challenge for modern chemical research is to nnderstand the molecular dynamics of 

FIGURE 1.1 Alchemists searched in vain for procedures that would turn base metals into gold. Their apparatus foreshadowed equipment in modern chemical laboratories. 

Chemistry is a relatively young science and its foundations weren t established until the last quarter of the 18th century. Before that, most chemists were known as alchemists—early entrepreneurs who sought to transform the properties of materials for economic gain (Fig. 1.1). For many centuries their obsession was to transform base metals, such as lead, into gold. They boldly assumed that the properties of one material could somehow be extracted from that material and transferred to another. If the essential properties—such as yellow color, softness, and ductility—could be assembled from various inexpensive sources, then gold could be created at great profit. 

To observers in the early 21st century, the mistake of the alchemists is immediately clear They did not follow the scientific method. In the scientific method, a new idea is accepted only temporarily, in the form of a hypothesis. It is then subjected to rigorous testing, in carefully controlled experiments. Only by surviving many such tests is a hypothesis elevated to become a scientific law. In addition to having explained the results of numerous experiments, a scientific law must be predictive failure to accurately predict the results of a new experiment is sufficient to invalidate a scientific law. Concepts or ideas that have earned the status of scientific laws by direct and repeated testing then can be applied with confidence in new environments. Had a proper set of tests been made in separate, independent experiments, the alchemists would have recognized that the properties of a material are, in fact, intrinsic, inherent characteristics of that material and cannot be separated from it. 

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