An important physiological reaction of nitric oxide (NO) is its interaction with the superoxide ion (O₂^–) to form the peroxynitrite ion (ONOO^–).
a. Write electron-dot structures for NO, O₂^–, and ONOO^–, and predict the O–N–O bond angle in ONOO^–.

Verified step by step guidance

1. <strong>Step 1:</strong> Draw the electron-dot structure for NO. Start by counting the total number of valence electrons. Nitrogen (N) has 5 valence electrons and oxygen (O) has 6 valence electrons, giving a total of 11 valence electrons. Distribute these electrons to satisfy the octet rule as much as possible, keeping in mind that NO is a radical with an unpaired electron.
2. <strong>Step 2:</strong> Draw the electron-dot structure for the superoxide ion, O₂^–. Oxygen has 6 valence electrons, so for O₂, you have 12 valence electrons. The extra negative charge adds one more electron, making it 13 electrons in total. Distribute these electrons to form a bond between the two oxygen atoms, and place the extra electron on one of the oxygens.
3. <strong>Step 3:</strong> Draw the electron-dot structure for the peroxynitrite ion, ONOO^–. Count the total valence electrons: O (6) + N (5) + O (6) + 1 (for the negative charge) = 18 electrons. Arrange these electrons to form bonds between the atoms, ensuring that the octet rule is satisfied for each atom as much as possible.
4. <strong>Step 4:</strong> Consider the resonance structures for ONOO^–. Since ONOO^– can have multiple valid electron-dot structures, draw the possible resonance forms to show the delocalization of electrons.
5. <strong>Step 5:</strong> Predict the O–N–O bond angle in ONOO^–. Consider the electron pair geometry around the nitrogen atom. Since ONOO^– is a bent molecule due to the presence of lone pairs on the nitrogen, the bond angle will be less than 120 degrees, typical for a bent molecular geometry.

Key Concepts

Electron-Dot Structures

Electron-dot structures, also known as Lewis structures, represent the valence electrons of atoms within a molecule. They illustrate how electrons are shared or transferred between atoms, helping to visualize molecular bonding and geometry. For nitric oxide (NO), the structure shows a double bond between nitrogen and oxygen, while the superoxide ion (O2–) has an unpaired electron, indicating its radical nature. Understanding these structures is essential for predicting molecular behavior and reactivity.

Bond Angles and Molecular Geometry

Bond angles are the angles formed between adjacent bonds in a molecule, which are influenced by the arrangement of electron pairs around a central atom. The molecular geometry of ONOO– can be predicted using VSEPR (Valence Shell Electron Pair Repulsion) theory, which states that electron pairs will arrange themselves to minimize repulsion. In ONOO–, the presence of resonance structures and lone pairs will affect the O–N–O bond angle, which is crucial for understanding the molecule's reactivity and interactions.

Reactivity of Nitric Oxide and Superoxide

Nitric oxide (NO) and superoxide (O2–) are both reactive species that play significant roles in biological systems. NO is a signaling molecule involved in various physiological processes, while O2– is a reactive oxygen species that can cause oxidative stress. Their interaction to form peroxynitrite (ONOO–) is a critical reaction that can lead to further biological effects, including cellular damage. Understanding the reactivity of these species is essential for grasping their physiological implications and the chemistry behind their interactions.