The International Union of Pure and Applied Chemistry ( IUPAC) has devised a system of nomenclature that begins with the names of the alkanes and can be adjusted from there to account for more complicated structures. These three representations of the structure of n-butane are not isomers because they all contain the same arrangement of atoms and bonds. For example, two alkanes have the formula C4H10: They are called n-butane and 2-methylpropane (or isobutane), and have the following Lewis structures:įigure 3. Hydrocarbons with the same formula, including alkanes, can have different structures. Properties such as melting point and boiling point (Table 1) usually change smoothly and predictably as the number of carbon and hydrogen atoms in the molecules change. Greater numbers of atoms in the molecules will lead to stronger intermolecular attractions (dispersion forces) and correspondingly different physical properties of the molecules. The number of carbon atoms present in an alkane has no limit. Condensed structural formulas for ethane and pentane are shown at the bottom of Figure 1, and several additional examples are provided in the exercises at the end of this chapter.Īll alkanes are composed of carbon and hydrogen atoms, and have similar bonds, structures, and formulas noncyclic alkanes all have a formula of CnH2n+2. These formulas have the appearance of a Lewis structure from which most or all of the bond symbols have been removed. Instead of the usual format for chemical formulas in which each element symbol appears just once, a condensed formula is written to suggest the bonding in the molecule. The structures of alkanes and other organic molecules may also be represented in a less detailed manner by condensed structural formulas (or simply, condensed formulas).

Because of the sp3 hybridization, the bond angles in carbon chains are close to 109.5°, giving such chains in an alkane a zigzag shape. Notice that the carbon atoms in the structural models (the ball-and-stick and space-filling models) of the pentane molecule do not lie in a straight line.

Carbon chains are usually drawn as straight lines in Lewis structures, but one has to remember that Lewis structures are not intended to indicate the geometry of molecules. The Lewis structures and models of methane, ethane, and pentane are illustrated in Figure 1. Each of the carbon atoms in an alkane has sp3 hybrid orbitals and is bonded to four other atoms, each of which is either carbon or hydrogen. This leads to differences in geometries and in the hybridization of the carbon orbitals.Īlkanes, or saturated hydrocarbons, contain only single covalent bonds between carbon atoms. We can distinguish several types of hydrocarbons by differences in the bonding between carbon atoms. The familiar plastics polyethylene, polypropylene, and polystyrene are also hydrocarbons. We use hydrocarbons every day, mainly as fuels, such as natural gas, acetylene, propane, butane, and the principal components of gasoline, diesel fuel, and heating oil. Many hydrocarbons are found in plants, animals, and their fossils other hydrocarbons have been prepared in the laboratory. In addition, hydrocarbons may differ in the types of carbon-carbon bonds present in their molecules.

Even though they are composed of only two types of atoms, there is a wide variety of hydrocarbons because they may consist of varying lengths of chains, branched chains, and rings of carbon atoms, or combinations of these structures. The simplest organic compounds contain only the elements carbon and hydrogen, and are called hydrocarbons. The existence of so many organic molecules is a consequence of the ability of carbon atoms to form up to four strong bonds to other carbon atoms, resulting in chains and rings of many different sizes, shapes, and complexities. The number of potential organic compounds has been estimated at 1060-an astronomically high number. The largest database of organic compounds lists about 10 million substances, which include compounds originating from living organisms and those synthesized by chemists.

Identify structural and geometric isomers of hydrocarbons.

Describe the reactions characteristic of saturated and unsaturated hydrocarbons.

Name saturated and unsaturated hydrocarbons, and molecules derived from them.

Explain the importance of hydrocarbons and the reason for their diversity.

Hydronium ion bonding and hybridization