THE BASICS A LITTLE CHEMISTRY

These are simplified rules for most elements (though not carbon or oxygen) more than one valence state is permitted, and the situation is in reality more complex generally, but the simple scheme will serve. So let us move on to more interesting compounds. 

Carbon, as we have seen, has the capacity to form long chains. With two carbons and hydrogen we get ethane, 

But it is also now obvious that, once we get beyond three carbon atoms, they can be linked in different ways. So butane, the fourth member of the alkane series, can take two forms, one linear, one branched  

Returning now to polyethylene, this polymer (which is known commercially as polythene) takes its name from the compound from which it is synthesized, namely ethylene  

This is the first of the family of olefins, or alkenes. Because the carbon atoms here carry fewer than thdr maximum possible number of hydrogens, this type of compound is termed unsaturated, whereas the alkanes are saturated compounds. (The terms saturated and unsaturated have entered common usage in relation to the good and bad dietary fats the good ones contain carbon-carbon double bonds.) An important difference between the properties of single and double bonds is that the atoms or groups 

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