Ozone Structure and Bonding Quiz

Fundamentals of Medicinal and Pharmaceutical Chemistry

• This course focuses on covalent bonding in physiologically important ions and molecules.
• Recommended reading is "General Chemistry - The Essential Concepts" by Chang and Goldsby 7e, Section 9.1, 9.2, 9.4 - 9.9.

Learning Outcomes

• Construct Lewis dot structures for diatomic and triatomic molecules using simple rules.
• Define resonance.
• Define bond order and its relation to bond strength/length
• Define free radical.
• Identify nitric oxide and superoxide ion and hydroxyl radical as free radicals.
• Define disproportionation (dismutation) reaction.
• Outline the equation for the disproportionation of superoxide and the role of superoxide dismutase
• Outline the equation for the reaction of nitric oxide and superoxide ion to give peroxynitrite.
• Recall the neurotoxicity of peroxynitrite.

Lewis Dot Structures

• A Lewis dot symbol shows the symbol of an element and one dot for each valence electron.
• Valence electrons are those found in the outermost shell.
• Valence electrons participate in bonding between atoms or ions.
• Lewis dot structures can represent bonding in molecules and ions.

Six-Step Procedure for Lewis Dot Structures

1. Count the valence electrons of each atom in the molecule, adjusting for charge.
2. Arrange the atoms in the molecule, with hydrogen (generally) excluded from central positioning. The atom with lowest electronegativity is usually the central atom.
3. Connect the central atom to the other atoms with single bonds (one pair of electrons).
4. Complete the octet rule (or duet rule for hydrogen) for the most electronegative atoms first, then add electrons to the central atom.
5. If the central atom has an incomplete octet, convert surrounding atom lone pairs into multiple bonds.
6. Indicate any resonance forms.

Electronegativity Trends

• Electronegativity increases across a period from left to right and decreases down a group.
• A table of electronegativity values is provided.

Lewis Dot Structure of NF₃

• The procedure for drawing a Lewis dot structure for NF₃ is outlined step-by-step, including valence electron counting, atom arrangement, and octet rule completion.

Lewis Dot Structure of O₃

• The procedure for drawing a Lewis dot structure for O₃ is outlined, addressing valence electron counting, atom arrangement, and resonance structures.

Resonance and Resonance Structures

• Resonance involves using multiple Lewis structures to represent a molecule when a single structure cannot accurately portray its bonding.
• Double-headed arrows indicate resonance between Lewis structures.

O-O Bond Properties in O₃

• The bond lengths in ozone (O₃) are identical, indicating a bond order between single and double bonds
• This is supported by the average/hybrid bond length and value.

Resonance Structures of O₃

• The actual structure of ozone (O₃) is a hybrid of its resonance structures.
• The bond order of each O-O bond is 1.5.

Bond Order

• Bond order indicates the approximate strength of a bond.
• It compares bonding strengths.
• Bond order = (Number of bonds) / (Number of connections)

Lewis Dot Structure for CO₃²⁻

• The procedure for drawing a Lewis dot structure for CO₃²⁻ is presented, including valence electron counting, atom arrangement, and resonance structure determination.
• The structure shows a central carbon atom and three surrounding oxygen atoms.
• Bond order calculations show each bond as 4/3.

Lewis Dot Structure for CO

• The procedure for drawing a Lewis dot structure for CO is outlined, demonstrating the valence electron counting, atom arrangement, and lack of resonance structures.

Isoelectronic

• Isoelectronic species have the same number of valence electrons and connectivity.
• Examples include: N, O+, CO, N₂, and NO+.

Limitations of Lewis Dot Structures

• Lewis structures may not accurately predict characteristics such as paramagnetism, especially for molecules like O₂.
• Paramagnetism is the property of a substance to be attracted to a magnetic field.
• Molecular orbital theory can explain such properties more fully than Lewis structures.

NO, Nitric Oxide

• Nitric oxide (NO) is a molecule of the year 1992.
• It's involved in blood pressure regulation, neurotransmission, and antimicrobial defense.
• In 1998 scientists won a Nobel prize for their work on NO.

Lewis Dot Structure for NO

• The procedure for drawing a Lewis dot structure for NO is outlined, showing valence electron counting, atom arrangement, and resonance forms.

NO Bond Length

• The bond length of NO varies depending on the specific compound.
• NO is a radical, meaning it has unpaired electrons.
• Radicals are highly reactive.

Reactive Oxygen Species (ROS)

• ROS are by-products of mitochondrial oxidation.
• Examples include superoxide ion (O₂⁻), peroxide ion (O₂²⁻), and hydroxyl radical (OH).
• ROS are damaging to biological systems.

Superoxide Ion (O₂⁻)

• The procedure to draw a Lewis dot structure for O₂⁻ is detailed, encompassing electron counting, atom arrangement, and resonance determinations.

Superoxide Ion and Superoxide Dismutase

• Superoxide dismutase catalyzes the disproportionation of superoxide ions.
• The disproportionation reaction converts superoxide to oxygen and peroxide.

Hydroxyl Radical (HO⁻)

• Hydroxyl radical is a highly reactive ROS.
• It's produced from reactions involving hydrogen peroxide.

Reactive Oxygen Species in Biological Systems

• ROS can oxidize various biological components, including lipids, proteins, and nucleic acids.
• This oxidation can cause cellular damage.

NO (Nitric Oxide) - Neurotoxic

• Excess NO leads to peroxynitrite formation.
• Peroxynitrite damages biomolecules.
• Superoxide dismutase helps mitigate excess NO.

Exceptions to the Octet Rule

• Some 2A and 3A elements form stable compounds with fewer than eight electrons around the central atom (e.g., Be, B).

Learning Outcomes Summary

• The summary of learning outcomes for this course focuses on drawing Lewis dot structures, resonance, bond strength and order, classifying radicals, understanding chemical reactions like disproportionation. The outcomes also cover the properties of reactive oxygen species and molecular modeling.