Question

Explain the difference between saturated hydrocarbons and unsaturated hydrocarbons.

Short answer

The main difference between saturated and unsaturated hydrocarbons lies in the type of carbon-carbon bonds present in the molecules. Saturated hydrocarbons, or alkanes, have only single C-C bonds and are fully "saturated" with hydrogen atoms (general formula: \(C_nH_{2n+2}\)). Unsaturated hydrocarbons, which include alkenes and alkynes, contain one or more double (C=C) or triple (C≡C) bonds, resulting in a decrease in the number of hydrogen atoms attached to the carbon atoms (general formulas: alkenes - \(C_nH_{2n}\); alkynes - \(C_nH_{2n-2}\)).

Step-by-step solution

Definition of Hydrocarbons

Hydrocarbons are organic compounds consisting only of carbon and hydrogen atoms. They can be divided into two main categories: saturated and unsaturated hydrocarbons. The key difference between these categories lies in the type of carbon-carbon bonds present in the molecules.

Saturated Hydrocarbons

Saturated hydrocarbons, also known as alkanes, are hydrocarbons in which all carbon-carbon (C-C) bonds are single bonds. This means that each carbon atom in the molecule is bonded to as many hydrogen atoms as possible, making it "saturated" with hydrogen. Their general formula is \(C_nH_{2n+2}\) (where n is the number of carbon atoms). An example of a saturated hydrocarbon is methane (CH4), which has one carbon atom bonded to four hydrogen atoms. Another example is ethane (C2H6), in which two carbon atoms are bonded together with each carbon atom also bonded to three hydrogen atoms.

Unsaturated Hydrocarbons

Unsaturated hydrocarbons, on the other hand, contain at least one double or triple bond between carbon atoms. There are two types of unsaturated hydrocarbons: alkenes and alkynes. - Alkenes are hydrocarbons containing at least one carbon-carbon double bond (C=C), with the general formula of \(C_nH_{2n}\) (where n is the number of carbon atoms). An example of an alkene is ethene (C2H4), which contains two carbon atoms with a double bond and two hydrogen atoms attached to each carbon. - Alkynes are hydrocarbons containing at least one carbon-carbon triple bond (C≡C), having the general formula \(C_nH_{2n-2}\) (where n is the number of carbon atoms). Ethyne (C2H2), also known as acetylene, is an example of an alkyne, with two carbon atoms connected by a triple bond and one hydrogen atom attached to each carbon.

Summary

In summary, the main difference between saturated and unsaturated hydrocarbons is the type of carbon-carbon bonds present in the molecules. Saturated hydrocarbons (alkanes) have only single C-C bonds and are fully "saturated" with hydrogen atoms, while unsaturated hydrocarbons (alkenes and alkynes) contain one or more double (C=C) or triple (C≡C) bonds within their structure, resulting in a decrease in the number of hydrogen atoms attached to the carbon atoms.

Key concepts

Saturated Hydrocarbons

Saturated hydrocarbons are organic compounds made entirely of carbon and hydrogen, where all the carbon-carbon bonds are single bonds. This means that each carbon atom forms as many bonds as possible with hydrogen atoms. Due to this complete bonding pattern, they are called "saturated".

In simple terms, saturated hydrocarbons are like a sponge fully soaked with water; in this case, carbon atoms are fully "soaked" with hydrogen.

Their chemical formula is typically denoted by \(C_nH_{2n+2}\), where \(n\) is the number of carbon atoms. Common examples include methane \((CH_4)\), which has one carbon atom, and ethane \((C_2H_6)\), with two carbon atoms.

• Methane is the simplest saturated hydrocarbon with one carbon bound to four hydrogens.
• Ethane consists of two carbons connected by a single bond, with each carbon further bonded to three hydrogens.

These hydrocarbons are also known as alkanes and are generally found in nature as fuels like natural gas and petrol.

Unsaturated Hydrocarbons

Unsaturated hydrocarbons differ from their saturated counterparts by having at least one double or triple carbon-carbon bond. This results in fewer hydrogen atoms bonded to the carbon atoms. Because they are not "saturated" with hydrogen atoms, they are aptly named unsaturated hydrocarbons.

There are two subtypes of unsaturated hydrocarbons:

• **Alkenes**, which have at least one double bond (\(C=C\)). For example, ethene \((C_2H_4)\) has a double bond between its two carbon atoms.
• **Alkynes**, which include at least one triple bond (\(C\equiv C\)). An example here is ethyne \((C_2H_2)\), with a triple bond between its carbons.

Unsaturated hydrocarbons are often found in plant oils and are used in chemical synthesis for plastics and other industrial applications. They can also undergo reactions that saturated hydrocarbons cannot, such as addition reactions, due to the presence of double or triple bonds.

Carbon-Carbon Bonds

The type of bonds between carbon atoms defines whether a hydrocarbon is saturated or unsaturated. The carbon atom is unique because it can form up to four covalent bonds due to its four available electrons.

In **saturated hydrocarbons**, all carbon-carbon bonds are single (\(C-C\)) bonds. This allows them to be fully saturated with hydrogen, hence no further atoms can be added easily.

**Unsaturated hydrocarbons** have one or more double (\(C=C\)) or triple (\(C\equiv C\)) carbon bonds, providing them unique chemical properties like reactivity in addition reactions.

Here's a simple breakdown:

• Single bonds (\(C-C\)): Seen in alkanes; they do not easily react with other substances.
• Double bonds (\(C=C\)): Found in alkenes; they can easily participate in addition reactions.
• Triple bonds (\(C\equiv C\)): Present in alkynes; even more reactive than double bonds, facilitating various chemical transformations.

Understanding these differences in bond types helps illuminate why saturated and unsaturated hydrocarbons have starkly different chemical properties and uses.

Alkanes

Alkanes are a type of saturated hydrocarbon characterized by only single carbon-carbon bonds (\(C-C\)). Because of these single bonds, alkanes have a complete set of hydrogen atoms bonded to their carbon framework, reflecting their saturated nature.

The general molecular formula for alkanes is \(C_nH_{2n+2}\), where \(n\) represents the number of carbon atoms. Therefore, for every additional carbon atom, two more hydrogen atoms are attached, ensuring the molecule retains a linear or branched structure with a relatively high hydrogen content.

• Examples of the simplest alkanes include methane (\(CH_4\)) and ethane (\(C_2H_6\)).
• As the longest carbon chain increases, alkanes assume different names (e.g., propane \((C_3H_8)\), butane \((C_4H_{10})\)), each with distinct boiling points and physical properties.

Alkanes are usually nonpolar molecules, making them excellent as fuels since they combust in oxygen to release energy. They are characterized by their relative inertness, not reacting easily with other chemical species, making them stable over a wide range of environments.

Alkenes and Alkynes

Alkenes and alkynes are the classes of unsaturated hydrocarbons and are known for their reactivity due to the double and triple bonds, respectively.

**Alkenes** contain at least one carbon-carbon double bond (\(C=C\)). This bond allows for additional atoms to "add" to the molecule, making them more chemically reactive than alkanes. Their general formula is \(C_nH_{2n}\).

• An example is ethene \((C_2H_4)\), which serves as a precursor for many industrial polymers.
• Alkenes can participate in polymerization reactions, forming long-chain polymers like polyethylene used in plastics.

**Alkynes** feature at least one carbon-carbon triple bond (\(C\equiv C\)), which makes them even more reactive. Their formula is \(C_nH_{2n-2}\).

• Ethyne \((C_2H_2)\), commonly known as acetylene, is an alkyne used in welding and cutting due to its high-temperature flame when burned in oxygen.
• The triple bond in alkynes provides them with distinct chemical properties, allowing reactions that aren't possible in alkanes or alkenes.

Understanding the structure and reactivity of these hydrocarbons is crucial for their application in the synthesis of a wide range of industrial and consumer products.