Lecture 9_9-23-25 Lewis Structures, Formal Charge File

Flashcards covering key concepts from CH101 lecture notes on Lewis Structures, Octet Rule, Bond Properties, Exceptions, Formal Charge, and Resonance Structures.

Lewis Structures

Diagrams that show the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.

Valence Electrons

The total number of outermost shell electrons present in atoms of a compound, adjusted for any charges.

Skeletal Structure

The basic arrangement of atoms in a molecule, typically showing single covalent bonds between atoms.

Central Atom

In a molecule, the least electronegative atom (excluding hydrogen) that is bonded to two or more other atoms.

Octet Rule

Fundamental principle stating that nonmetal atoms tend to achieve closed valence shells of 8 electrons by sharing electrons.

Bond Order

The number of chemical bonds between a pair of atoms. A single bond has a bond order of 1, a double bond has 2, and a triple bond has 3.

Bond Energy

The energy input required to break a bond and fully separate two bound atoms.

Bond Length

The distance between the nuclei of two atoms engaged in a bond.

Relationship between Bond Order, Energy, and Length

Increasing bond order leads to increasing bond energy and decreasing bond length.

Duet Rule (Hydrogen)

An exception to the octet rule where hydrogen atoms only need 2 electrons to achieve a stable configuration, usually forming 1 bond.

Incomplete Octets

An exception to the octet rule where a central atom has fewer than eight valence electrons due to a shortage of electrons (e.g., BeH2, elements in Group 3A like B or Al).

Free Radicals

Molecules or ions that have an odd number of electrons, resulting in an incomplete octet on the central atom (e.g., NO2).

Expanded Octets

An exception to the octet rule where a central atom has more than eight valence electrons; typically occurs for atoms in and beyond the third period (e.g., P, S, As).

Formal Charge

An electron counting method for covalent bonds used to determine the most plausible Lewis structure; it assumes bonding electrons are shared equally between atoms.

Formal Charge Formula

Formal Charge = (Valence Electrons) - (Nonbonding Electrons) - (1/2 * Bonding Electrons).

Associated Electrons (for Formal Charge)

For formal charge calculation, associated electrons are all of an atom's nonbonding electrons plus half of its bonding electrons.

Resonance Structure

An alternate Lewis structure depiction of the same molecule where atom connectivity remains identical, the number of electrons remains the same, but the electrons are simply distributed differently.

Preferred Resonance Structure Rules

The most preferred resonance structure minimizes the number of atoms with nonzero formal charges, places negative formal charges on the more electronegative atoms, and ensures all atoms requiring an octet have one.