Question

Use the octet rule to draw Lewis dot structures for all the stable molecules with the molecular formula \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\) . (Hint: There are three total molecules.)

Short answer

The three molecules are propanol, isopropanol, and methoxyethane.

Step-by-step solution

Understanding the Octet Rule

The octet rule states that atoms tend to form molecules by sharing electrons such that each atom has eight electrons in its valence shell. This rule explains the formation of stable molecules through covalent bonding.

Analyzing the Molecular Formula

The given molecular formula is \(

C_{3}H_{8}O

\), indicating three carbon atoms, eight hydrogen atoms, and one oxygen atom. Each carbon can form four bonds, hydrogen can form one bond, and oxygen can form two bonds.

Constructing Lewis Structures - Molecule 1: Propanol

For the first molecule, align the carbon atoms in a chain (C-C-C) and add the hydroxyl group (-OH) to one of the terminal carbons. Distribute the remaining hydrogen atoms to satisfy each carbon's four bonds. Structure: CH3-CH2-CH2-OH.

Constructing Lewis Structures - Molecule 2: Isopropanol

For the second molecule, use a branched carbon alignment (C-C(OH)-C). Attach the hydroxyl group to the middle carbon. Distribute hydrogen atoms to fulfill each carbon's octet. Structure: CH3-CHOH-CH3.

Constructing Lewis Structures - Molecule 3: Methoxyethane

For the third molecule, align two carbon atoms in a chain with the oxygen atom forming an ether linkage between a third carbon. Structure: CH3-CH2-O-CH3, with the oxygen connecting two carbons and each carbon satisfying its required bonds with hydrogen.

Key concepts

Octet Rule

The octet rule is a fundamental principle in chemistry. It states that atoms are most stable when they have a complete set of eight valence electrons, mimicking the electron configuration of noble gases. Atoms achieve this stable state by forming chemical bonds. Many elements abide by this rule, especially the carbon, nitrogen, oxygen, and fluorine atoms found in organic compounds.

Atoms can fulfill the octet rule through various types of bonds, most commonly covalent bonds, where they share electrons with other atoms.

• Carbon typically forms four covalent bonds, making it very versatile in forming complex molecular structures.
• Oxygen, on the other hand, forms two bonds, contributing to molecules like alcohols and ethers.
• Hydrogen, although unable to follow the octet rule since it can only hold two electrons, often pairs with other elements to help them achieve their desired octet.

Understanding the octet rule helps us predict and explain the shapes and stability of molecules.

Covalent Bonding

Covalent bonding is one of the key forces that hold atoms together within a molecule. This type of bond occurs when two atoms share one or more pairs of electrons to fill their outer electron shells under the octet rule. This sharing allows each atom involved to resemble the electron configuration of noble gases.

Here's how covalent bonding manifests in organic molecules:

• Carbon, with its four valence electrons, will form four covalent bonds to satisfy the octet rule, as seen in organic structures like methane (CH extsubscript{4}) and here in C extsubscript{3}H extsubscript{8}O molecules.
• Oxygen typically forms two covalent bonds due to its six valence electrons, thus reaching a total of eight electrons when paired with other atoms. This is evident in alcohols and ethers where oxygen is central to the structure.
• Hydrogen forms single covalent bonds because it needs only one additional electron to complete its share—achieving the stable configuration of helium rather than noble gases.

Covalent bonds are pivotal not only for stability but also in defining the properties and reactivity of molecules.

Molecular Structures

Molecular structures are visual representations that help us see how atoms are arranged within a molecule. By utilizing Lewis dot structures, we can visualize covalent bonds and ensure that atoms follow the octet rule.

Let's consider the molecular structures of C extsubscript{3}H extsubscript{8}O:

• Propanol: Here, three carbon atoms form a chain, with a terminal hydroxyl group (-OH), allowing oxygen and carbon atoms to adhere to the octet rule neatly.
• Isopropanol: In this arrangement, a hydroxyl group is bonded to the middle carbon of a branched chain, a structure common to secondary alcohols.
• Methoxyethane: Exhibits an ether linkage where an oxygen atom connects a methyl and an ethyl group, showcasing how oxygen can also participate in forming ethers.

By studying molecular structures, students can understand the diverse ways atoms bond and form complex three-dimensional configurations. This knowledge helps to predict how molecules will interact in chemical reactions.