Question

Draw the straight-chain alkane with the formula \(\mathrm{C}_{5} \mathrm{H}_{12}\) as a condensed structure and as a line drawing.

Short answer

Pentane is \( \mathrm{CH}_{3}\mathrm{-CH}_{2}\mathrm{-CH}_{2}\mathrm{-CH}_{2}\mathrm{-CH}_{3} \); line drawing is a straight line with 4 segments.

Step-by-step solution

Identify the Alkane

The given formula is \( \mathrm{C}_{5}\mathrm{H}_{12} \), which represents an alkane with 5 carbon atoms. This means we are dealing with pentane, as it is a straight-chain alkane with 5 carbon atoms.

Understand the Structure

Pentane, being a straight-chain alkane, will have a linear arrangement of the 5 carbon atoms, connected by single bonds (\( \mathrm{C-C} \)). Each carbon will be bonded to hydrogen atoms to satisfy the tetravalency of carbon, meaning each carbon forms 4 bonds in total.

Draw the Condensed Structure

To write the condensed structure, we arrange the carbon atoms linearly and indicate the number of hydrogen atoms bonded to each carbon atom. The condensed formula is expressed as \( \mathrm{CH}_{3}\mathrm{-CH}_{2}\mathrm{-CH}_{2}\mathrm{-CH}_{2}\mathrm{-CH}_{3} \).

Create the Line Drawing

In a line drawing, carbon atoms and hydrogen atoms are implicitly represented; each vertex or end of a line represents a carbon atom. The line drawing of pentane will appear as a straight line with four segments (3 corners or vertices), as carbon atoms are connected in a series.

Key concepts

Alkane

Alkanes are a fascinating group of organic compounds. They are part of a larger class called hydrocarbons, which are made up of hydrogen and carbon atoms.
An alkane has only single bonds connecting the carbon atoms in the chain, making it a saturated hydrocarbon. This means every carbon atom is fully bonded to the maximum number of hydrogen atoms possible. For example, pentane is an alkane with five carbon atoms, represented by the molecular formula \( \mathrm{C}_5\mathrm{H}_{12} \).
Understanding alkanes is crucial because they serve as foundational building blocks for more complex molecules and have various uses in everyday life, such as fuels and lubricants.

Chemical Structure

The chemical structure of a molecule reveals the arrangement of atoms within it. For alkanes like pentane, the chemical structure is all about the order of carbon and hydrogen atoms.
Each carbon atom forms four bonds, and in a straight-chain alkane, these bonds create a continuous zig-zag line. This clear understanding helps you predict the behavior and properties of the molecule.
By knowing the structure, chemists can determine the molecule’s boiling point, solubility, and how it might react with other substances. Pentane’s structure of five linearly arranged carbon atoms ensures that it is a simple and stable molecule.

Condensed Structure

The condensed structure is a concise way to represent a molecule. Instead of drawing every single bond, we write the chemical formula in segments.
For pentane, the condensed structure is \( \mathrm{CH}_3\mathrm{-CH}_2\mathrm{-CH}_2\mathrm{-CH}_2\mathrm{-CH}_3 \). Each segment shows a carbon atom and its directly attached hydrogen atoms.
This method saves time and space, making it easier to quickly convey the molecule's makeup in text. Condensed structures are useful for quickly sharing information about organic molecules without having to draw detailed diagrams.

Line Drawing

Line drawings are one of the simplest ways to represent organic molecules. This method omits carbon and hydrogen labels, using lines to signify carbon-carbon bonds.
Each endpoint or vertex in a line drawing represents a carbon atom. For pentane, you would draw a straight line with a few kinks, each kink indicating a carbon atom.
Line drawings help streamline busy chemical diagrams, allowing professionals to easily discern complex molecules without clutter. This approach is prevalent in organic chemistry due to its clarity and efficiency.

Carbon-Hydrogen Bonds

Carbon-hydrogen bonds are fundamental to organic chemistry. Each carbon atom in a molecule forms bonds with hydrogen atoms to satisfy its tetravalency—meaning carbon needs to form four bonds to be stable.
In alkanes like pentane, carbon-hydrogen bonds are non-polar because the electronegativity difference between carbon and hydrogen is small. This gives alkanes their relatively low reactivity.
Even though these bonds may seem simple, they are crucial in determining a hydrocarbon's physical properties, such as boiling and melting points, and their role in energy storage due to their stability.