Question

Several compounds have the formula \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}\). Write Lewis structures for two of these compounds where the three carbon atoms are bonded to each other in a chain. The hydrogen and the oxygen atoms are bonded to the carbon atoms.

Short answer

Question: Identify two compounds with the molecular formula C₃H₆O in which all three carbon atoms are bonded in a chain, and provide their Lewis structures. Answer: The two compounds are propanal and propanone (acetone). Their Lewis structures are: Propanal: ``` H | H - C - C - C = O | | H H | H ``` Propanone (Acetone): ``` H | H - C - C = O - C - H | | H H | H ```

Step-by-step solution

Identify two isomers with the molecular formula C₃H₆O

There are several isomers possible with the molecular formula C₃H₆O. We need to find two where the three carbon atoms are bonded in a chain. The two isomers that meet this criteria are propanal and propanone (also known as acetone).

Draw the Lewis structures for the two isomers

Now, we need to draw the Lewis structures for propanal and propanone. For propanal: 1. Arrange the atoms in order, with the carbon atoms forming a chain: H-C-C-C-O. 2. Add in the hydrogen atoms around the carbon atoms, making sure each carbon atom forms four bonds in total. The hydrogen and the oxygen atoms will be bonded to carbon atoms. 3. Fill in the electrons around the oxygen atom to complete the octet rule. For propanone: 1. Arrange the atoms, with the carbon atoms forming a chain: H-C-C-C. 2. Place the oxygen atom between the second and third carbon atom, creating a double bond. 3. Add in the hydrogen atoms around the carbon atoms, making sure each carbon atom forms a total of four bonds. The hydrogen and the oxygen atoms will be bonded to carbon atoms. 4. Fill in the electrons around the oxygen atom to complete the octet rule. So, the Lewis structures for the two compounds are: Propanal: ``` H | H - C - C - C = O | | H H | H ``` Propanone (Acetone): ``` H | H - C - C = O - C - H | | H H | H ```

Key concepts

Isomers

Isomers are fascinating variations within chemistry that share the same molecular formula but differ in the arrangement of atoms. In simpler terms, isomers have the same kinds and numbers of atoms but differ in their structural layout. This difference leads to unique physical and chemical properties for each isomer.
Isomers can be categorized into various types. Here, we focus on structural isomers where atoms are connected in different orders. For example, with the molecular formula \( \mathrm{C}_3\mathrm{H}_6\mathrm{O} \), propanal and propanone (acetone) are two structural isomers with distinctive arrangements:

• Propanal: This compound features a chain of carbon atoms where the oxygen atom is double-bonded to the end carbon atom.
• Propanone: Here, the oxygen atom is placed between two carbon atoms, creating a double-bond with one of them.

Understanding isomers helps in grasping how molecules can distinctly behave even though they appear to be composed of the same building blocks.

Molecular Formula

The molecular formula of a compound is a simple yet powerful tool that provides valuable information about the composition of molecules in terms of atoms. It tells you the exact number and types of atoms present but not how these atoms are connected.
For instance, the molecular formula \( \mathrm{C}_3\mathrm{H}_6\mathrm{O} \) indicates that each molecule consists of three carbon atoms, six hydrogen atoms, and one oxygen atom. However, without more information, this formula does not reveal how these atoms are chemically bonded or arranged within the molecule.
When examining isomers, the molecular formula alone is not enough to provide a clear picture of the molecule's structure. That's where the structural formula and Lewis structures come in handy, as they illustrate the actual arrangement of atoms, which is crucial for understanding the molecule's chemical behavior.
Thus, mastering the interpretation of molecular formulas is foundational to chemistry, providing a stepping stone to deeper insights into the characteristics and reactivity of compounds.

Octet Rule

The octet rule is a guiding principle in chemistry that helps predict the arrangement of atoms in a molecule. It suggests that atoms tend to combine in such a way that each atom has eight electrons in its valence shell, resembling the electron configuration of a noble gas.
In practice, this rule is pivotal when drawing Lewis structures. Take the compound propanal as an example. We ensure that each carbon atom forms four bonds, and the oxygen atom reaches eight valence electrons with lone pairs and bonds included. This often involves lone pairs of electrons and bonding arrangements, like double bonds, to complete the octet.
While the octet rule is quite reliable for many elements, especially those in the second row of the periodic table, it's essential to remember there are exceptions. Some molecules, particularly those containing elements from the third period onwards, can have expanded octets due to available d orbitals.
By adhering to the octet rule, you can craft more accurate Lewis structures and deepen your understanding of how molecules like propanal or acetone are built and function.