ASP - Classification of Matter (Lesson)
Classifying Matter
Chemistry, in its simplest form, is the study of both matter and energy. Not only that, it is the study of how matter can change from one form to another in addition to the energy change associated with these transformations. In order to help us understand these changes in matter it is helpful to classify matter into certain categories. While there are many potential ways that matter can be classified, one of the most common ways is to categorize it based on its fundamental makeup. In other words, matter can be classified into two broad categories based on whether it is a pure substance or a mixture (a mixture of pure substances).
Pure Substances
Pure substances can be furthered categorized based on their atomic level makeup. For example, a sample of pure gold, when investigated on the smallest level possible, would consist of nothing but gold atoms. If these atoms are broken down into even smaller particles, they would no longer retain the properties of gold. Gold could therefore be categorized as an element.
Alternatively, consider a sample of ordinary table salt. Table salt has the chemical formula NaCl and when investigated in the same manner as gold, it would be determined that the smallest sample of NaCl, which still retains all of the properties of NaCl, would be a combination of both sodium and chlorine atoms. If you break these apart, it could no longer be considered the same substance. Sodium chloride (NaCl) would therefore be categorized as a compound.
Mixtures
In the same way that pure substances can be categorized based on how many different elements they contain, mixtures can be separated into two unique categories as well. The dividing feature here is a bit different, however. There are two categories of mixtures, and these categories are classified based on their appearance. Simply, types of mixtures can be distributed with the answer to a simple question: Does the mixture have visibly distinguishable features or does it have a uniform composition? If there are clearly distinguishable features then the mixture is said to be heterogeneous (from the Latin “hetero” which means different or dissimilar). If there are no distinguishable features and the entire mixture has the same consistency and appearance throughout then the mixture is best classified as homogeneous (from the Greek “homos” which means same).
The particle sketches below show various mixtures and pure substances. Each of the uniquely colored dots represents a unique element. The dots that are directly connected to each other represent molecules. Remember there are seven elements that exist as diatomic molecules (two atoms of the same element chemically bound to each other): hydrogen, oxygen, fluorine, bromine, iodine, nitrogen, and chlorine. Click on the plus signs in the image below to reveal descriptions of the various mixtures and pure substances.
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