The school chemistry, a new text-book for high schools and academies by Avery Elroy M

Author:Avery, Elroy M[cKendree], 1844- [from old catalog]
Language: eng
Format: epub, pdf
Tags: Chemistry
Publisher: New York, Cincinnati [etc.] American book company
Published: 1904-03-25T05:00:00+00:00

in the formation of many compounds of the same composition, but with different physical properties. These compounds that have the same percentage composition and that differ in the arrangement of the atoms in the molecule, and hence have different physical properties, are called isomers.

(«) Isomers that differ in molecular weight are called polymers, of which acetylene (C 2 H 2 ) and benzene (C 6 H 6 ) are examples. Isomers that have the same molecular weight are called metamers, of which ammonium cyanate (NH 4 CNO) and urea [(NH 2 ) 2 CO] are examples. In like manner, aldehyde and ethylene oxide have the same molecular weight, and their elements are combined in the same proportion (C 2 H 4 0), but they differ widely in their chemical properties.

253. Molecular Structure. — These isomeric forms increase in number very rapidly as the complexity of the molecule increases. There are three known isomers having the formula of C 5 H 12 ; five, having the formula C 6 H 14 . There are nine possible forms of C 7 H 16 , four of which are known. It has been calculated that for the hydrocarbon C 13 H 28 , there are 799 possible isomers. In such ways, an almost endless variety of carbon compounds arises.

(a) The recognized variations in molecular structure that underlie isomerism have made it important for chemists to resolve the empirical formulas into atomic groups that shall at least suggest some of the known facts in any given case. By way of illustration, we may take one of these isomeric compounds, acetic acid (C 2 H 4 () 2 ). Experiment shows that acetic acid is monobasic; i.e., that only one of its four hydrogen atoms can be replaced by a metal to form a salt. This suggests that one of the four hydrogen atoms is held in the molecule in a way different from the way or ways in which the other three are held. This fact is expressed by writing the formula for acetic acid, H(C 2 H 3 0 2 ).

It is also possible to substitute one atom of chlorine for one of hydrogen, and one of oxygen in the acetic acid molecule, yielding C 2 H 3 0C1. jSTo greater part of the hydrogen and oxygen can be thus

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