Page:Outlines of Physical Chemistry - 1899.djvu/41

 II. 2, S 2 , &c. ; 0" or S" replacing H 2.

IV. C0C1 2, C0 2 , CS 2 , &c. ; 0" or S" replacing Cl 2 or H 2. HCN ; N" replacing H 3.

Without trying to explain the cause of this attractive force of the atoms, we may consider the atoms as possessing a number of poles ; and, by the mutual union of these, the atoms become linked together to form molecules or systems in equilibrium, in which all the poles are saturated.

Structural Formula

Knowing the molecular weight of a compound, the number and nature of the atoms contained in the molecule, as well as the valency of these atoms, it is possible to arrive at the chemical constitution of the substance, that is, the manner in which the atoms are joined together.

For this purpose it is necessary to form all the possible arrangements of the given atoms, and, if there be more than one arrangement possible, make a choice of the most suitable.

(a) The first part of the problem is purely mathema- tical and can always be solved. The difficulty increases with the number^ valency, and variety of atoms which go to make up the compound. The discovery of all possible arrangements becomes an extremely difficult problem for the numerous compounds of carbon, for which not only the linkage of the carbon atoms (so variable in itself) must be kept in view, but where account must also be taken of the positions on the carbon structure of other atoms of different kinds, which enter into the molecule.

Thus, for the first few members of the hydrocarbon series C n H2n +2 we have the following possible carbon structures : l

1 The free valencies of carbon being saturated by hydrogen, the first combination cited represents CJB^. the second C 8 H 8, the third C 4 H I0, and the fourth C 5 H 12.

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