See Carbon Catenate. Catenate, Carbon, Catenate.
Alkanes, the Simplest of Hydrocarbons
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You can predict the formula from the name for pentane on up, if you know what number the Greek root in the name represents (pent- means five carbons) and that the hydrogens will always be two more than twice the carbons.
Pentane=5-ane, 5×2+2=12, therefore: C5H12
enne- sounds lame so let’s arbitrarily switch just this once to Latin: non- =9
For the first four alkanes, you can’t get the number from the root, but the other part of the rule still works, the carbon times two plus two part. To remember the order of the first four, you can use this mnemonic device: ME Play Ball. (Methane, Ethane, Propane, and Butane.)
Wonder why carbon times two plus two works? Of course not. That’s not on the test. But for the curious, consider a molecular diagram:
This is butane, but the pattern is true for all of ’em. All of the carbons will be bonded to two hydrogens, except for the outermost, which are able to accept one more hydrogen each. Therefore: carbon times two plus two.