Problem 175 - Chemistry: An Atoms-Focused Approach

Question

Draw the Lewis structure for dimethyl ether, \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O}\), given that the structure contains an oxygen atom bonded to two carbons: \(\mathrm{C}-\mathrm{O}-\mathrm{C}.\)

Step-by-Step Solution

Answer

Answer: The Lewis structure for dimethyl ether (C2H6O) is: H H | | H-C-O-C-H • | • • • This structure contains an oxygen atom bonded to two carbon atoms (C-O-C), with each carbon atom bonded to three hydrogen atoms. The oxygen atom has two bonds and two lone pairs of electrons, satisfying the octet rule for all elements in the molecule.

Step 1: Determine the total number of valence electrons

We first need to find the total number of valence electrons in the C2H6O molecule. Carbon has 4 valence electrons, hydrogen has 1, and oxygen has 6. Since there are two carbon atoms, six hydrogen atoms, and one oxygen atom in the molecule, we have: (2 Carbon atoms × 4 electrons) + (6 Hydrogen atoms × 1 electron) + (1 Oxygen atom × 6 electrons) = 8 + 6 + 6 = 20 valence electrons Thus, the C2H6O molecule has 20 valence electrons.

Step 2: Arrange the atoms

Now, we will arrange the atoms as described in the given molecular skeleton: C-O-C. The oxygen atom will be placed between the two carbon atoms, and each carbon atom will be bonded to three hydrogen atoms. H H | | H-C-O-C-H | H

Step 3: Connect atoms with bonds and distribute remaining electrons

Next, we will distribute the 20 valence electrons in the structure, placing them first as bonding electrons between each atom pair: H H | | H-C-O-C-H | H Since there are 7 bonds in the structure (6 C-H bonds and 1 O-C bond), we have used 14 out of the 20 valence electrons. We still have 6 electrons remaining.

Step 4: Complete octets for other atoms

Now, we will place the remaining 6 electrons on atoms to complete their octets. Carbon atoms already have full octets, with 4 bonds each, so we will focus on the oxygen atom. Oxygen needs two more electron pairs to satisfy the octet rule. Thus, we will place the remaining 6 electrons on the oxygen atom as three lone pairs: H H | | H-C-O-C-H • | • • •

Step 5: Confirm octets for all atoms

Finally, let's confirm that each atom in the structure has a complete octet (or a duet for hydrogen). - Hydrogen (6 atoms): Each H atom has one bond (2 electrons), which is a complete duet. - Carbon (2 atoms): Each C atom has 4 bonds (8 electrons), which is a complete octet. - Oxygen (1 atom): The O atom has 2 bonds and 2 lone pairs (8 electrons), which is a complete octet. All atoms in the C2H6O structure now have complete octets/duets. Here is the final Lewis structure for dimethyl ether: H H | | H-C-O-C-H • | • • •

Key Concepts

Valence Electrons

Valence electrons are the outermost electrons of an atom, playing a key role in chemical bonding. These electrons determine how atoms interact with each other to form compounds. When drawing Lewis structures, it's crucial to correctly count the total number of valence electrons available. This ensures you create accurate depictions of molecules and understand their behavior.

• Carbon (C) has 4 valence electrons,
• Hydrogen (H) has 1 valence electron,
• Oxygen (O) has 6 valence electrons.

With dimethyl ether, which has two carbon atoms, six hydrogen atoms, and one oxygen atom, the calculation goes like this:

• 2 Carbon atoms × 4 electrons = 8 electrons
• 6 Hydrogen atoms × 1 electron = 6 electrons
• 1 Oxygen atom × 6 electrons = 6 electrons

This adds up to 20 valence electrons in total. Understanding how these electrons are distributed helps in figuring out the molecule's shape and chemical reactivity.

Octet Rule

The octet rule is a fundamental concept in chemistry stating that atoms tend to bond in such a way that they have eight electrons in their valence shell, replicating the electron configuration of noble gases. The idea is to achieve a stable electron arrangement which makes molecules more stable.
In the case of the dimethyl ether (C₂H₆O) molecule, each atom strives to satisfy this rule:

• Carbon, having four valence electrons, forms four covalent bonds to complete its octet.
• Oxygen has six valence electrons and tends to make two bonds and also can hold two lone pairs to achieve a full octet.
• Hydrogen is an exception to the octet rule, aiming for a duet, which is simply having two electrons.

In the Lewis structure of dimethyl ether, the carbon atoms have complete octets (8 electrons: 4 from the bonds), oxygen also achieves an octet with 2 bonds and 2 lone pairs, while each hydrogen atom is part of a single bond completing its duet.

Dimethyl Ether

Dimethyl ether is a simple example of an ether, a class of organic compounds characterized by an oxygen atom bonded to two alkyl or aryl groups. Its chemical formula is C₂H₆O, and its structural formula is typically expressed as CH₃OCH₃.
In the Lewis structure for dimethyl ether, the oxygen atom connects two carbon atoms. The molecule’s shape and electron distribution dictate chemical properties such as polarity and reactivity.

• The C-O-C arrangement denotes an ether bond, providing the molecule with its characteristic properties.
• Being a polar molecule, dimethyl ether interacts with other substances via dipole interactions.
• As an ether, it is relatively inert but will react under certain conditions, particularly in the presence of acids or halogens.

Learning about dimethyl ether helps understand not just this compound but the fundamental behavior of ethers in chemistry.