Chemical Compound - Non-chemical Definitions, History, Early Theories Of Compounds, Modern Theory Of Compounds, Types Of Compounds
iron mixture sulfur elements
A compound is a substance composed of two or more elements chemically combined with each other. Historically, the distinction between compounds and mixtures was often unclear. Today, however, the two can be distinguished from each other on the basis of three primary criteria. First, compounds have constant and definite compositions, while mixtures may exist in virtually any proportion. A sample of water always consists of 88.9% oxygen and 11.1% hydrogen by weight. However, a mixture of hydrogen and oxygen gases can have any composition whatsoever.
Second, the elements that make up a compound lose their characteristic elemental properties when they become part of the compound, while the elements that make up a mixture retain those properties. In a mixture of iron and sulfur, for example, black iron granules and yellow sulfur crystals can often be recognized. Also, the iron can be extracted from the mixture by means of a magnet, or the sulfur can be dissolved out with carbon disulfide. One part of the compound is called iron(II) sulfide, however, both iron and sulfur lose these properties.
Third, the formation of a compound is typically accompanied by the evolution of light and heat, while no observable change is detectable in the making of a mixture. A mixture of iron and sulfur can be made simply by stirring the two elements together. But the compound iron(II) sulfide is produced only when the two elements are heated. Then, as they combine with each other, they give off a glow.
Additional Topics
Prior to the 1800s, the term compound had relatively little precise meaning. When used, it was often unclear as to whether one was referring to what scientists now call a mixture or to what they now know as a compound. During the nineteenth century, the debate as to the meaning of the word intensified, and it became one of the key questions in the young science of chemistry. A critical aspect of t…
It is difficult for a reader in the 1990s to appreciate the challenge facing a chemist in 1850 who was trying to understand the nature of a compound. Today it is clear that atoms of elements combine with each other to form, in many cases, molecules of a compound. Even the beginning chemistry student can express this concept with facility by using symbols and formulas, as in the formation of iron(I…
The most fundamental change that has taken place in chemistry since the nineteenth century is that atomic theory now permits an understanding of chemical compounds from the particle level rather than from purely empirical data. That is, as our knowledge of atomic structure has grown and developed, our understanding of the reasons that atoms (elements) combine with each other has improved. For exam…
Most of the ten million or so chemical compounds that are known today can be classified into a relatively small number of subgroups or families. More than 90% of these compounds are, in the first place, designated as organic compounds because they contain the element carbon. In turn, organic compounds can be further subdivided into a few dozen major families such as the alkanes, alkenes, alkynes, …
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