Aldehydes have a wide flammable range from 3% to 55% in air, they are toxic and may polymerize. They have moderate boiling and flash points and high ignition temperatures. Fires involving aldehydes should be fought with polar-solvent-type foams because water may be ineffiective. Aldehydes may also form explosive peroxides as they age, much the same way ethers do. Aldehydes are composed of a carbon atom double-bonded to an oxygen atom with a oxygen hydrogen atom on the other carbon connection. Aldehydes are carbonyls and, therefore, polar. The degree of polarity is much the same as ketone and ester, and much less than alcohol and organic acid. They are miscible with water and require the use of polar solvent foams to extinguish fires. Aldehydes have the general formula of R-CHO. There is one radical attached to the carbon atom of the aldehyde functional group. Aldehydes are one of the three derivatives in which the carbon atom in the functional group is counted when naming the compound. The alternate terms for one- and two-carbon radicals are also used with the aldehydes. A one-car-bon aldehyde uses "form", and a two-carbon uses "acet." The aldehydes are named by identifying the radical, naming it, and ending with the word "aldehyde." Aldehydes may also be named in the same manner as the alternate for alcohols; however, with the aldehydes, the ending is "al" instead of "ol." For example, a one-carbon aldehyde is called formaldehyde, with the alternate name of methanal. In the following examples, the structures molecular for mulas, and names are shown for one-, two-, and three- carton aldehydes. The polarity of the carbonyls is somewhat less than that of the alcohols and the organic acids (Photo 5.17)