Problem 11 - Chemistry and Chemical Reactivity

Question

Which of the following compounds can be an alkane? (a) \(\mathrm{C}_{2} \mathrm{H}_{4}\) (b) \(\mathrm{C}_{5} \mathrm{H}_{12}\) (c) \(\mathrm{C}_{14} \mathrm{H}_{30}\) (d) \(\mathrm{C}_{7} \mathrm{H}_{8}\)

Step-by-Step Solution

Answer

The alkane compounds are (b) \(\mathrm{C}_5\mathrm{H}_{12}\) and (c) \(\mathrm{C}_{14}\mathrm{H}_{30}\).

Step 1: Understanding Alkanes

Alkanes are hydrocarbons with single bonds between carbon atoms and follow the general formula \(\mathrm{C}_n\mathrm{H}_{2n+2}\), where \(n\) is the number of carbon atoms.

Step 2: Analyze Each Option

We evaluate each compound to see if it fits the \(\mathrm{C}_n\mathrm{H}_{2n+2}\) formula. (a) \(\mathrm{C}_2\mathrm{H}_4\): Follows \(\mathrm{C}_2\mathrm{H}_6\), so it's not an alkane.(b) \(\mathrm{C}_5\mathrm{H}_{12}\): Follows \(\mathrm{C}_5\mathrm{H}_{2 \times 5 + 2} = \mathrm{C}_5\mathrm{H}_{12}\), so it's an alkane.(c) \(\mathrm{C}_{14}\mathrm{H}_{30}\): Follows \(\mathrm{C}_{14}\mathrm{H}_{2 \times 14 + 2} = \mathrm{C}_{14}\mathrm{H}_{30}\), so it's an alkane.(d) \(\mathrm{C}_7\mathrm{H}_8\): Follows \(\mathrm{C}_7\mathrm{H}_{16}\), so it's not an alkane.

Step 3: Conclusion

Only the compounds \(\mathrm{C}_5\mathrm{H}_{12}\) and \(\mathrm{C}_{14}\mathrm{H}_{30}\) match the alkane formula, indicating they are indeed alkanes.

Key Concepts

Hydrocarbons

Hydrocarbons are organic compounds composed entirely of hydrogen ( H ) and carbon ( C ) atoms. They are fundamental to organic chemistry and serve as the building blocks of more complex organic compounds. These substances are categorized based on the types of bonds between carbon atoms. There are three main classes of hydrocarbons:

• **Alkanes:** These are saturated hydrocarbons with single C-C bonds. They follow the general formula C_nH_{2n+2} and are often referred to as paraffins.
• **Alkenes:** These are unsaturated hydrocarbons containing at least one double C=C bond. Their general formula is C_nH_{2n} .
• **Alkynes:** These are unsaturated hydrocarbons with one or more triple C≡C bonds and have a general formula C_nH_{2n-2} .

Understanding hydrocarbons is crucial because they form the base of all organic chemistry, allowing for the creation of diverse substances found in fuels, plastics, and pharmaceuticals. Each type lends unique characteristics based on the presence of single, double, or triple bonds.

Molecular Formula

The molecular formula of a compound indicates the types and numbers of atoms present within a molecule. It is an essential tool in chemistry for identifying the exact composition of a compound. For example, alkanes, a type of hydrocarbon, have a specific molecular formula pattern: C_nH_{2n+2} .

• This formula means that for every 'n' carbon atoms, there are 2n+2 hydrogen atoms.
• It is useful for identifying whether a substance is an alkane or another type of hydrocarbon.
• For instance, the molecular formula of C_5H_{12} fits the alkane pattern, confirming it as an alkane.

The molecular formula helps chemists understand not only the composition of a substance but also predict its chemical behavior and reactivity. This pattern recognition enables the classification and study of various organic compounds based on shared structures and properties.

Chemical Bonding

Chemical bonding refers to the connections between atoms that allow the formation of molecules and compounds. In hydrocarbons like alkanes, bonding involves sharing electrons to achieve stability.

• **Single Bonds (σ-bonds):** In alkanes, carbon atoms connect through single sigma bonds, depicted as C-C bonds. These are strong and allow rotation around the bond axis.
• **Double and Triple Bonds:** These occur in alkenes and alkynes, respectively, and involve pi bonds in addition to sigma bonds. Though stronger, they limit the rotation, affecting the molecule's structure.
• **Polarity:** Alkanes are nonpolar due to the electron-sharing symmetry in C-C and C-H bonds, leading to low reactivity compared to other hydrocarbons with different bond types.

Chemical bonding is indispensable for understanding molecular stability, shape, and reactivity. In alkanes, it influences properties like boiling and melting points, solubility, and intermolecular interactions, making it fundamental in fields like chemistry and biochemistry.