Matter according to Its Composition Elements. Compounds, and Mixtures

Classifying Matter according to Its Composition Elements, Compounds, and Mixtures 

Iq addition to classifying matter according to its state, we can classify it according to its composition, as shown in the following chart  

The first division in the classification of matter is between a pure substance and a mixture. A pure substance is made up of only one component and its composition is invariant (it does not vary from one sample to another). The components of a pure substance can be individual atoms or groups of atoms joined together. For example, helium, water, and table salt (sodium chloride) are all pure substances. Each of these substances is made up of only one component helium is made up of helium atoms, water is made up of water molecules, and sodium chloride is made up of sodium chloride units. The composition of a pure sample of any one of these is always exactly the same (because you can t vary the composition of a substance made np of only one component). 

A mixture, by contrast, is composed of two or more components in proportions that can vary from one sample to another. For example, sweetened tea, composed primarily of water molecules and sugar molecules (with a few other substances mixed in), is a mixture. We can make tea slightly sweet (a smaU proportion of sugar to water) or very sweet (a large proportion of sugar to water) or any level of sweetness in between. 

We can categorize pure substances themselves into two types—elements and compounds—depending on whether or not they can be broken down (or decomposed) into simpler substances. Helium, which we just noted is a pure substance, is also a good example of an element, a substance that cannot be chemically broken down into simpler substances. Water, also a pure substance, is a good example of a compound, a substance composed of two or more elements (in this case hydrogen and oxygen) in a fixed, definite proportion. On Earth, compounds are more common than pure elements because most elements combine with other elements to form compounds. 

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