Problem 78 - Introductory Chemistry Atoms First

Question

Ethers are compounds of \(\mathrm{C}, \mathrm{H}\), and \(\mathrm{O}\) that are often used as solvents. One particular ether molecule has the formula \(\mathrm{C}_{2} \mathrm{H}_{6} \mathrm{O} .\) The structure is such that both carbons are attached to the oxygen atom, and there are no \(\mathrm{O}-\mathrm{H}\) bonds. Starting with dot diagrams for the atoms, draw a dot diagram for this ether molecule. How many bonding pairs does the molecule have? How many lone pairs?

Step-by-Step Solution

Answer

The ether molecule's dot diagram has the following structure: H - C - O - C - H It consists of 8 bonding pairs (6 C-H bonds and 2 C-O bonds) and 2 lone pairs on the oxygen atom.

Step 1: Determine Valence Electrons

For each atom in the molecule, determine the number of valence electrons. Carbon (C) has 4 valence electrons, hydrogen (H) has 1, and oxygen (O) has 6.

Step 2: Create Preliminary Dot Diagram

Begin by arranging the atoms. Since each of the two carbon atoms is attached to the oxygen atom, our starting structure will be O in the center with each of the carbons on either side: C-O-C. Now, we need to add hydrogen atoms and place their electrons.

Step 3: Add Hydrogen Atoms

We know there are 6 hydrogen atoms. Add 3 hydrogen atoms around each carbon atom. Now, create single bonds by placing one electron from each hydrogen atom with one of the valence electrons from the carbon (C-H) and oxygen (O-H) atoms.

Step 4: Distribute Bonding Pairs

At this stage, there should be 3 bonding pairs between each carbon atom and its surrounding hydrogen atoms (C-H bonds). The oxygen atom has two valence electrons, which will form a bond with each of the carbon atoms (C-O bonds). So, in total, there are 8 bonding pairs in the molecule: 6 C-H bonds and 2 C-O bonds.

Step 5: Identify Lone Pairs

After distributing bonding pair electrons, the oxygen atom still has 4 valence electrons which are not involved in any bonding. These will be placed as two lone pairs on the oxygen atom. These lone pairs will not form any bond, either with carbon or with hydrogen. In conclusion, the ether molecule's dot diagram has the structure: H | H - C - O - C - H | H It consists of 8 bonding pairs (6 C-H bonds and 2 C-O bonds) and 2 lone pairs on the oxygen atom.

Key Concepts

Valence Electrons

Valence electrons are the outer shell electrons that are available for bonding in an atom. They are crucial as they determine how an atom will interact with other atoms. In the provided exercise, the valence electrons are the starting point for determining the ether molecule's bonding structure. Each carbon atom has 4 valence electrons, each hydrogen atom has 1 valence electron, and the oxygen atom has 6 valence electrons. When these valence electrons are properly accounted for, they guide the formation of bonds and the structure of the molecule.

Understanding the count of valence electrons is the initial step in predicting how atoms connect. In our case, valence electrons help us to define the specific shape and bonding pairs present in the ether molecule. This is vita lfor students studying organic compounds like ethers to comprehend the behavior and reactivity of these molecules.

Dot Diagrams

Dot diagrams, or Lewis dot structures, are graphical representations used to visualize the valence electrons of an atom and how they may bond with other atoms. In the exercise, the dot diagram begins with an atomic level arrangement and builds up to illustrate the bonding within the ether molecule. Here, dots are used to signify valence electrons and lines or dot pairs represent chemical bonds.

Creating a dot diagram for a molecule like ether involves positioning the atoms in a plausible layout and then organizing the electrons to reflect bonding pairs and lone pairs. This visual aid significantly enhances a student's ability to grasp how atoms bond in molecules and is a powerful instructional tool for the study of chemistry, particularly when addressing the construction of complex molecules.

Bonding Pairs

Bonding pairs are sets of valence electrons that are shared between atoms, forming a chemical bond. They can be represented in dot diagrams as a line connecting two atoms. For our ether molecule, there are 8 bonding pairs: 6 from carbon to hydrogen bonds (C-H), and 2 from carbon to oxygen bonds (C-O).

Formation of Bonds

• C-H Bond: Each hydrogen atom is sharing one electron with a carbon atom.
• C-O Bond: Each oxygen atom is sharing two electrons with each carbon atom.

Grasping the concept of bonding pairs is essential in chemistry since these interactions dictate molecules' stability and properties.

Lone Pairs

Lone pairs are valence electrons that are not shared with other atoms and thus do not participate in bonding. They are represented in dot diagrams as pairs of dots adjacent to an atom. In the case of the ether molecule, we see that the oxygen atom has two lone pairs after forming the C-O bonds. These electron pairs take up space and can affect molecule shape, but because they are not shared, they don’t create a bond.

Lone pairs can significantly alter the behavior and reactivity of a molecule. For instance, in the context of solvents like ethers, the presence of lone pairs on the oxygen atom can engage in hydrogen bonding, affecting solubility and interaction with other molecules. Students should pay careful attention to lone pairs as they advance their understanding of molecular structures.