Question

(i) Ethyne (ii) Ethene (iii) Ethane (iv) Propyne (v) Propene (vi) Propane

Short answer

Question: Provide the molecular formula and structure for each of the following hydrocarbons: ethyne, ethene, ethane, propyne, propene, and propane. Answer: 1. Ethyne has a molecular formula of C2H2, with a structure of H-C≡C-H. 2. Ethene has a molecular formula of C2H4, with a structure of H2C=CH2. 3. Ethane has a molecular formula of C2H6, with a structure of CH3CH3. 4. Propyne has a molecular formula of C3H4, with a structure of H-C≡C-CH3. 5. Propene has a molecular formula of C3H6, with a structure of H2C=CH-CH3. 6. Propane has a molecular formula of C3H8, with a structure of CH3CH2CH3.

Step-by-step solution

Molecular Formula of Ethyne

Ethyne consists of two carbon atoms and two hydrogen atoms, which is a member of the alkynes group. The molecular formula for ethyne is C2H2.

Structure of Ethyne

Ethyne has a triple bond between the two carbon atoms. The structure of ethyne is H-C≡C-H.

Molecular Formula of Ethene

Ethene consists of two carbon atoms and four hydrogen atoms, which is a member of the alkenes group. The molecular formula for ethene is C2H4.

Structure of Ethene

Ethene has a double bond between the two carbon atoms. The structure of ethene is H2C=CH2.

Molecular Formula of Ethane

Ethane consists of two carbon atoms and six hydrogen atoms, which is a member of the alkanes group. The molecular formula for ethane is C2H6.

Structure of Ethane

Ethane has a single bond between the two carbon atoms with each carbon atom bonded to three hydrogen atoms. The structure of ethane is CH3CH3.

Molecular Formula of Propyne

Propyne consists of three carbon atoms and four hydrogen atoms, which is a member of the alkynes group. The molecular formula for propyne is C3H4.

Structure of Propyne

Propyne has a triple bond between the first and second carbon atoms. The structure of propyne is H-C≡C-CH3.

Molecular Formula of Propene

Propene consists of three carbon atoms and six hydrogen atoms, which is a member of the alkenes group. The molecular formula for propene is C3H6.

Structure of Propene

Propene has a double bond between the first and second carbon atoms. The structure of propene is H2C=CH-CH3.

Molecular Formula of Propane

Propane consists of three carbon atoms and eight hydrogen atoms, which is a member of the alkanes group. The molecular formula for propane is C3H8.

Structure of Propane

Propane has a single bond between three carbon atoms with each carbon atom bonded to two or three hydrogen atoms. The structure of propane is CH3CH2CH3.

Key concepts

Alkanes

Alkanes are an essential group of hydrocarbons that are saturated, meaning they only have single bonds between carbon atoms. This saturation gives them the formula \(C_nH_{2n+2}\), where \(n\) represents the number of carbon atoms. Because of their single bonds, alkanes are quite stable and are termed "paraffins."

• For example, ethane (\(C_2H_6\)) is a simple alkane with two carbon atoms linked by a single bond, and each carbon atom is bonded to three hydrogen atoms.
• Similarly, propane (\(C_3H_8\)) consists of three carbon atoms, also connected by single bonds, forming a simple chain structure.

Alkanes play significant roles in various fields, including fuel sources like natural gas and gasoline. Their stability and simplicity make them ideal for basic structural components in organic synthesis.

Alkenes

Alkenes are another crucial type of hydrocarbons, characterized by the presence of at least one double bond between carbon atoms. This characteristic makes them unsaturated hydrocarbons. Alkenes follow the general formula \(C_nH_{2n}\). The double bond gives alkenes unique chemical properties, allowing them to participate in addition reactions, where molecules can be added across the double bond.

• Ethene (\(C_2H_4\)) is the simplest alkene. It includes a double bond between the two carbon atoms and forms the foundation for many polymers, including polyethylene.
• Another example is propene (\(C_3H_6\)), which also has a double bond between the first and second carbon atoms.

Alkenes are essential in manufacturing chemicals and plastics, making them indispensable in the industrial world.

Alkynes

Alkynes are a fascinating group of hydrocarbons that contain at least one triple bond between carbon atoms. This feature makes them highly unsaturated. The general molecular formula for alkynes is \(C_nH_{2n-2}\). The triple bond not only makes alkynes more reactive than alkanes and alkenes but also gives them distinct physical properties.

• The simplest alkyne is ethyne (known as acetylene, \(C_2H_2\)), with a triple bond between its two carbon atoms, making it a linear molecule.
• Propyne (\(C_3H_4\)) has a similar structure with a triple bond between the first and second carbon atoms.

Often used in welding torches and as precursors for organic synthesis, alkynes are crucial in industrial applications.

Molecular Formula

The molecular formula of a compound shows the exact number of each type of atom present in the molecule, helping us understand the compound's composition. For hydrocarbons, molecular formulas are especially useful for determining the type of hydrocarbon (alkane, alkene, or alkyne) and predicting their properties.

• Ethyne's formula (\(C_2H_2\)) indicates two carbon and two hydrogen atoms, classifying it as an alkyne.
• Ethene (\(C_2H_4\)) and ethane (\(C_2H_6\)) differ by their hydrogen count, reflecting their different saturation levels and physical properties.

By examining the molecular formula, chemists can quickly deduce important information about a hydrocarbon's bonding and reactivity.

Chemical Structure

The chemical structure of hydrocarbons describes how the atoms within a molecule are arranged in space and how they are bonded together. This arrangement profoundly affects the compound's chemical properties and behavior. Visual representations, such as Lewis structures or line drawings, help in understanding these arrangements.

• For example, ethyne's structure is represented as \(H-C\equiv C-H\), showing a triple bond between the carbon atoms.
• In contrast, ethane is shown as \(CH_3CH_3\), highlighting the single bonds without any unsaturation.

Understanding chemical structures allows chemists to predict reactions and interactions between different molecules, proving essential in the synthesis and development of new materials.