Lecture 10_9-25-25 Resonance, Molecular Geometry File

Vocabulary flashcards covering key concepts from the lecture on Resonance and Molecular Geometry, including definitions for resonance, Lewis structures, formal charge, VSEPR, electron and molecular geometries, and sigma/pi bonds.

Resonance structure

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

Resonance Structure Hierarchy Rule 1

In the most preferred resonance structure, each atom that requires an octet has an octet.

Resonance Structure Hierarchy Rule 2

In the most preferred resonance structure, the total number of atoms with nonzero formal charges is minimized.

Resonance Structure Hierarchy Rule 3

If a nonzero formal charge has to exist, it should be placed on the most appropriate atom, considering electronegativity.

Steps for Drawing Lewis Structures (1-2)

1) Count the number of valence electrons. 2) Place the least electronegative, non-H atom in the center (if 3+ atoms), then draw single bonds.

Steps for Drawing Lewis Structures (3-5)

3) Place remaining valence electrons as lone pairs. 4) Convert lone pairs to additional bonds for octets. 5) Calculate formal charge for each atom.

Formal Charge (FCA)

Calculated as: Valence Electrons (VE) - Non-bonding Electrons (NB) - 1/2 Bonding Electrons (BE).

Bond Order (for equally favored Lewis structures)

The sum of bond orders in all perfectly equally favored Lewis structures divided by the number of perfectly equally favored Lewis structures.

VSEPR (Valence Shell Electron-Pair Repulsion)

A model used to translate 2D Lewis structures into 3D molecular geometry, minimizing repulsion between electron pairs.

Electron Domain

Any single bond, double bond, triple bond, or lone pair of electrons around a central atom; each counts as 1 electron domain.

Electron Domain Geometry: Linear

Occurs when there are 2 electron domains around a central atom, with a bond angle of 180°.

Molecular Geometry: Linear

Occurs when there are 2 electron domains and no lone pairs on the central atom (e.g., CO2), with a bond angle of 180°.

Electron Domain Geometry: Trigonal Planar

Occurs when there are 3 electron domains around a central atom, with a bond angle of 120°.

Molecular Geometry: Trigonal Planar

Occurs when there are 3 electron domains and no lone pairs on the central atom (e.g., BF3), with a bond angle of 120°.

Molecular Geometry: Bent (3 electron domains)

Occurs when there are 3 electron domains and 1 lone pair on the central atom (e.g., SO2), with a bond angle of 120°.

Electron Domain Geometry: Tetrahedral

Occurs when there are 4 electron domains around a central atom, with a bond angle of 109.5°.

Molecular Geometry: Tetrahedral

Occurs when there are 4 electron domains and no lone pairs on the central atom (e.g., CH4), with a bond angle of 109.5°.

Molecular Geometry: Trigonal Pyramidal

Occurs when there are 4 electron domains and 1 lone pair on the central atom (e.g., NH3), with a bond angle of 109.5°.

Molecular Geometry: Bent (4 electron domains)

Occurs when there are 4 electron domains and 2 lone pairs on the central atom (e.g., H2O), with a bond angle of 109.5°.

Single Bond

Consists of 1 sigma (σ) bond and 0 pi (π) bonds.

Double Bond

Consists of 1 sigma (σ) bond and 1 pi (π) bond.

Triple Bond

Consists of 1 sigma (σ) bond and 2 pi (π) bonds.

Sigma (σ) bond

Forms from direct end-to-end orbital overlap on the internuclear axis (directly between the two nuclei), typically involves hybridized orbitals, and has no nodal plane.

Pi (π) bond

Forms through orbital overlap above and below the internuclear axis, has a nodal plane on the internuclear axis, can only form after a sigma bond, and primarily involves p orbitals.