HYDROCARBONS 57 



or more atoms of H for something for which it has 

 a greater affinity ; or some other ion more strongly 

 negative may be able to displace the H and occupy 

 its place ; thus the OH ion carries a stronger electro- 

 negative charge than H.* Indeed, OH ions play a 

 very active part in the molecular changes of an 

 enormous number of organic compounds, for by OH 

 displacing any H the compound is indirectly oxidised. 

 If the methane molecule is robbed of one of its 

 H atoms by a migrating OH ion or any other ion 

 having that power, it leaves the combination with a 

 free valency which demands satisfaction. What is 

 left is methyl, CH 3 , a monovalent ion, which will 

 seize upon the free valency of similar molecules. 

 Ethane is formed by union of two such ions, thus : 



CH 3 -CH 3 or 2CH 4 - 2H + 20H = 2H 2 + C 2 H 6 . 



But methane may be stripped of two hydrogen 

 atoms, leaving CH 2 , a rest or divalent ion with two 

 unsatisfied valencies. These also may be saturated 

 by joining ions. Such molecules form open chains, 

 and may be composed of a number of ions or links 

 of a like character. In this manner series of com- 

 pounds are formed of which the following are 

 examples : 



Ethane, C 2 H 6 = CH 3 -CH 3 . 

 Propane, C 3 H 8 = CH 3 -CH 2 -CH 3 . 

 Butane, C 4 H 10 = CH 3 -CH 2 -CH 2 -CH 3 . 

 Pentane, C 5 H 12 = 

 Hexane, C 6 H 14 - 



* H is positive; but some ions may have their electrical 

 reaction changed from negative to positive or vice versa. The 

 acid anions are all negative whether they contain H or not. 



