Problem 115 - Chemistry: An Atoms-Focused Approach

Question

Radiation exposure leads to the ionization of water to \(\mathrm{H}_{2} \mathrm{O}^{+},\) which reacts to form \(\mathrm{H}_{3} \mathrm{O}^{+}\) and \(\mathrm{OH}\). Draw Lewis structures for these three molecules or molecular ions.

Step-by-Step Solution

Answer

Question: Draw the Lewis structures for \(\mathrm{H}_{2}\mathrm{O}^{+}\), \(\mathrm{H}_{3}\mathrm{O}^{+}\), and \(\mathrm{OH}\), and describe the steps involved in creating these structures. Answer: The Lewis structures for the given molecules are as follows: \(\mathrm{H}_{2}\mathrm{O}^{+}\): O / \ H H . \(\mathrm{H}_{3}\mathrm{O}^{+}\): O /|\ H H H \(\mathrm{OH}\): O / \ H .. .. To create these structures, follow these steps: 1. Determine the number of valence electrons for each element (H: 1, O: 6). 2. For the charged molecules, add or subtract electrons based on their charge. 3. Place the oxygen atom at the center and attach the hydrogen atoms. 4. Distribute the remaining valence electrons to complete the octet rule for oxygen (with exceptions in some cases).

Step 1: Determine valence electrons

Find the number of valence electrons for each element in the molecules. Hydrogen (H) has 1 valence electron, and oxygen (O) has 6 valence electrons.

Step 2: Draw Lewis structure for \(\mathrm{H}_{2}\mathrm{O}^{+}\)

For \(\mathrm{H}_{2}\mathrm{O}^{+}\), we have 2 hydrogen atoms and 1 oxygen atom, so we start with 2 * 1 + 6 = 8 valence electrons. Since it has a positive charge, we subtract 1, which gives us 7 valence electrons to distribute. 1. Place the oxygen atom in the center and attach the 2 hydrogen atoms to it. 2. Distribute the remaining 5 valence electrons to complete the octet rule for oxygen. In this case, oxygen will only have 5 electrons around it, which is an exception. The Lewis structure for \(\mathrm{H}_{2}\mathrm{O}^{+}\) is: O / \ H H .

Step 3: Draw Lewis structure for \(\mathrm{H}_{3}\mathrm{O}^{+}\)

For \(\mathrm{H}_{3}\mathrm{O}^{+}\), we have 3 hydrogen atoms and 1 oxygen atom, so we start with 3 * 1 + 6 = 9 valence electrons. Since it has a positive charge, we subtract 1, which gives us 8 valence electrons to distribute. 1. Place the oxygen atom in the center and attach the 3 hydrogen atoms to it. 2. Distribute the remaining 5 valence electrons to complete the octet rule for oxygen. The Lewis structure for \(\mathrm{H}_{3}\mathrm{O}^{+}\) is: O /|\ H H H

Step 4: Draw Lewis structure for \(\mathrm{OH}\)

For \(\mathrm{OH}\), we have 1 hydrogen atom and 1 oxygen atom, so we start with 1 * 1 + 6 = 7 valence electrons to distribute. 1. Place the oxygen atom in the center and attach the hydrogen atom to it. 2. Distribute the remaining 6 valence electrons to complete the octet rule for oxygen. The Lewis structure for \(\mathrm{OH}\) is: O / \ H .. ..

Key Concepts

Valence Electrons

Valence electrons are the outermost electrons in an atom. They play a crucial role in chemical bonding, as they are the ones involved in forming bonds between atoms. Each element has a specific number of valence electrons:

• Hydrogen (H) has 1 valence electron.
• Oxygen (O) has 6 valence electrons.

In the context of Lewis structures, knowing the number of valence electrons helps us determine how atoms share electrons to achieve stable configurations. For example, in the structure of \(\mathrm{H}_{2}\mathrm{O}^{+}\), we must account for 7 valence electrons due to its positive charge, leading to a specific arrangement of atoms and electrons.

Ionization

Ionization refers to the process by which an atom or molecule gains or loses electrons, resulting in a charged ion. In the case of the molecules discussed:

• \(\mathrm{H}_{2}\mathrm{O}^{+}\) forms from \(\mathrm{H}_{2}\mathrm{O}\) by losing an electron, resulting in a positive charge.
• Similarly, \(\mathrm{H}_{3}\mathrm{O}^{+}\) is formed when \(\mathrm{H}_{2}\mathrm{O}\) bonds with another hydrogen ion \(\mathrm{H}^{+}\).

Ionization changes the distribution of valence electrons, affecting how atoms bond together. For instance, the loss of an electron in \(\mathrm{H}_{2}\mathrm{O}^{+}\) means fewer electrons to distribute, leading to an unconventional configuration where the octet rule isn't fully satisfied for the central oxygen.

Octet Rule

The octet rule is a fundamental concept in chemistry, stating that atoms tend to bond in such a way that they each end up with 8 valence electrons, achieving a noble gas-like configuration. This rule is a guiding principle in drawing Lewis structures:

• In a typical scenario, oxygen, with its 6 valence electrons, aims to complete its octet by sharing electrons with hydrogen atoms.
• Yet, in molecules like \(\mathrm{H}_{2}\mathrm{O}^{+}\) and \(\mathrm{OH}\), the octet rule might not be fully applied because of ionization or the presence of charges.

The \(\mathrm{H}_{3}\mathrm{O}^{+}\) ion, however, allows oxygen to satisfy the octet by sharing its valence electrons with three hydrogen atoms. Understanding these exceptions is crucial, as it highlights how electron distribution is sometimes adjusted due to external influences like charges.