Changes

A [[pure substance]] (Latin ''purus'', from [[Greek language|Greek]] '''πυρ''' or ''pyr'' fire and '''πυροω''' ''pyroo'' I refine) is any substance having unique and defining properties. The concept of a pure substance requires one to separate the substance from all other substances ''without'' any change to that substance. One can, for example, separate the constituent [[metal]]s of an alloy without changing any one of them--but if one separates the [[hydrogen]] and [[oxygen]] in water, one obtains two new substances having properties radically different from those of the compound of which they were once part.

A '''pure substance''' (Latin ''purus'', from [[Greek language|Greek]] '''πυρ''' or ''pyr'' fire and '''πυροω''' ''pyroo'' I refine) is any substance having unique and defining properties. The concept of a pure substance requires one to separate the substance from all other substances ''without'' any change to that substance. One can, for example, separate the constituent [[metal]]s of an alloy without changing any one of them—but if one separates the [[hydrogen]] and [[oxygen]] in water, one obtains two new substances having properties radically different from those of the compound of which they were once part.

Pure substances are either [[chemical element]]s or [[chemical compound]]s. An element or [[molecular compound]] consists of only one type of atom or molecule.<ref>Wile, Dr. Jay L. ''Exploring Creation With Chemistry''. Apologia Educational Ministries, Inc. 1998</ref> An [[ionic compound]] can also be a pure substance, but must contain not more than three different species of ion in a ratio expressible in single digits. Any one of these ions may be monatomic or polyatomic, however.

Pure substances are either [[chemical element]]s or [[chemical compound]]s. An element or [[molecular compound]] consists of only one type of atom or molecule.<ref>Wile, Dr. Jay L. ''Exploring Creation With Chemistry''. Apologia Educational Ministries, Inc. 1998</ref> An [[ionic compound]] can also be a pure substance, but must contain not more than three different species of ion in a ratio expressible in single digits. Any one of these ions may be monatomic or polyatomic, however.

==== Specific gravity ====

==== Specific gravity ====

Closely related to density, ''[[specific gravity]]'' is a [[dimensionless]] ratio of the density of the substance to the density of a standard--typically another substance, usually a liquid, in which the substance in question is suspended. The usual standard of specific gravity is water, in which case the specific gravity is numerically equivalent to the density. But one can also define the specific gravity of a substance in, for example, an organic liquid, such as benzene.

Closely related to density, ''[[specific gravity]]'' is a [[dimensionless]] ratio of the density of the substance to the density of a standard—typically another substance, usually a liquid, in which the substance in question is suspended. The usual standard of specific gravity is water, in which case the specific gravity is numerically equivalent to the density. But one can also define the specific gravity of a substance in, for example, an organic liquid, such as benzene.

=== Melting point ===

=== Melting point ===

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== See Also ==

== See also ==

*[[Chemical element]]

*[[Chemical element]]

*[[Chemical compound]]

*[[Chemical compound]]

[[Category:Chemistry]]

[[Category:Chemistry]]