Problem 21 - Chemistry The Central Science

Question

(a) Why are alkanes said to be saturated? (b) Is \(\mathrm{C}_{4} \mathrm{H}_{6}\) a saturated hydrocarbon? Why or why not?

Step-by-Step Solution

Answer

Alkanes are considered saturated because they contain only single covalent bonds and have the maximum number of hydrogen atoms bonded to their carbon atoms. \(\mathrm{C}_{4} \mathrm{H}_{6}\) is not a saturated hydrocarbon, as it does not follow the general formula for alkanes \((C_nH_{2n+2})\) and must contain double or triple bonds between carbon atoms.

Step 1: Part (a): Understanding Alkanes and Saturation

Alkanes are a class of organic compounds that contain only carbon (C) and hydrogen (H) atoms. The carbon atoms in alkanes are connected to each other by single covalent bonds, and each carbon atom is bonded to hydrogen atoms, resulting in each carbon atom having four total bonds. Alkanes are considered saturated hydrocarbons because all the carbon atoms have the maximum number of hydrogen atoms bonded to them. This means there are no double or triple bonds between carbon atoms that would allow the molecule to bond with additional hydrogen atoms. In other words, alkanes are "saturated" with hydrogen atoms.

Step 2: Part (b): Determining if \(\mathrm{C}_{4} \mathrm{H}_{6}\) is a Saturated Hydrocarbon

To determine if \(\mathrm{C}_{4} \mathrm{H}_{6}\) is a saturated hydrocarbon, we can use the general formula for alkanes, which is \(C_nH_{2n+2}\). In this formula, n represents the number of carbon atoms in the compound. We have 4 carbon atoms in \(\mathrm{C}_{4} \mathrm{H}_{6}\). Plugging this into the formula, we get: \(C_4H_{2(4)+2} = C_4H_{10}\) Since the given hydrocarbon has a chemical formula of \(\mathrm{C}_{4} \mathrm{H}_{6}\) and not \(C_4H_{10}\), it is not an alkane and is, therefore, not a saturated hydrocarbon. This means that there must be double or triple bonds in the compound, allowing it to react with additional hydrogen atoms.

Key Concepts

Alkanes

Alkanes are the simplest type of hydrocarbon, made up of only carbon and hydrogen atoms. What makes them unique is that the carbon atoms are connected through single covalent bonds. This type of bonding results in each carbon atom forming four bonds in total, either with other carbon atoms or with hydrogen atoms.

Because of the single bond structure, no additional atoms can be added without breaking the existing bonds. This makes them very stable and less reactive compared to other hydrocarbons, such as alkenes and alkynes which have double or triple bonds. The chemical structure of alkanes results in a straight or branched chain formation, and they are sometimes referred to as paraffins. The general formula for alkanes is \(C_nH_{2n+2}\) where \(n\) is the number of carbon atoms.

Alkanes can range from simple forms like methane (\(CH_4\)) to more complex molecules, and they are primarily found in natural sources like natural gas and petroleum.

Hydrocarbon Saturation

Hydrocarbon saturation refers to the extent to which hydrogen atoms can bond with carbon atoms. In the context of alkanes, this means that they have the maximum possible number of hydrogen atoms attached to their carbon backbone.

Because all the carbon-carbon bonds in alkanes are single, there are no available bonds that could form additional connections with hydrogen. This is why alkanes are called 'saturated'. They are fully filled with hydrogen atoms. Understanding this concept is essential because it determines the chemical behavior and properties of the hydrocarbons.

For example, \(C_4H_6\) does not follow the alkane formula \(C_nH_{2n+2}\). Therefore, it is unsaturated, indicating the presence of double or triple bonds that allow room for more hydrogen atoms, as seen in alkenes or alkynes.

Chemical Bonding in Organic Chemistry

In organic chemistry, understanding chemical bonding is fundamental. It holds the key to how different organic molecules interact and react. Alkanes provide an excellent introduction to this as they exemplify single covalent bonding. Each carbon atom in alkanes forms four single bonds that can link to other carbons or hydrogen atoms.

When we consider other hydrocarbons like alkenes and alkynes, they have double and triple bonds, respectively, between carbon atoms. These multiple bonds alter the compound's properties, including reactivity and stability.

• Single bonds (\(C-C\)) in alkanes are quite stable, making these compounds less reactive.
• Double bonds (\(C=C\)) in alkenes increase the possibility of reactions because they can open up to attach to other atoms.
• Triple bonds (\(C\equiv C\)) in alkynes make them even more reactive due to the even higher energy multiple bonds.

Chemical bonding determines how organic compounds function, providing a framework for predicting the behavior of molecules during chemical reactions. By understanding these bonding principles, students can master the reasoning behind why certain hydrocarbons are classified as saturated or unsaturated.