Introduction to Hydrocarbons Alkanes Organic Chemistry Introduction to Hydrocarbons Alkanes

What is Organic Chemistry This is the branch of chemistry describing the structure and behaviors of compounds composed primarily of the elements Carbon and Hydrogen. Just like general chemistry, there are a number of classes of compounds within this branch of the field. Hydrocarbons are simply one of those groups of classes.

Hydrocarbons This group of compounds within the field of Organic Chemistry consists of compounds containing ONLY carbon and hydrogen. There are three separate classes of hydrocarbons – the bonding between the carbon atoms differentiates the classes.

Alkanes These are hydrocarbons that have only single bonds between the carbon atoms. The carbon atoms are all in sp3 hybrids. These alkanes can be identified by the ratio of carbons to hydrogens. That ratio is best described as CnH(2n+2) Examples include the formulas CH4 C2H6 C3H8 C4H10 Notice how each of the formulas has the correct ratio of atoms of each element.

Drawing Alkanes Remember that the Carbon atoms will be in sp3 hybrids and therefore, each carbon atom will form 4 bonds. If there is more than one carbon atom, start by connecting them in a chain. Then add the Hydrogen atoms on the outside of that carbon “backbone”.

Alkane Example H H H H C C C H H H H Remember that since all of the carbon atoms are in sp3 hybrids, the bond angles between all of the atoms is actually 109.5 degrees. The molecule is not “flat” as it is drawn, but is instead a “zig-zag” shape.

Naming Alkanes The key to naming these compounds is to learn the prefixes that correspond to the number of carbon atoms in the formula. All that has to be added is the suffix “-ane” because the compound is an alkane. C = meth C2 = eth C3 = prop C4 = but C5 = pent C6 = hex C7 = hept C8 = oct C9 = non C10 = dec

Therefore: CH4 = methane C2H6 = ethane C3H8 = propane C4H10 = butane C5H12 = pentane C6H14 = hexane C7H16 = heptane C8H18 = octane C9H20 = nonane C10H22 = decane Notice how each of these compounds has the described ratio of Carbon atoms to Hydrogen atoms