Chemistry Chp 9 - Molecular Geometry and Bonding Theories

Flashcards covering key concepts from the lecture on Chemical Bonding II, including molecular geometry, VSEPR model, valence bond theory, hybridization, and molecular orbital theory.

Electron-domain geometry

The arrangement of electron domains (bonds and lone pairs) around the central atom.

Molecular geometry

The arrangement of bonded atoms.

Steps to determine electron-domain and molecular geometries

1. Draw the Lewis structure of the molecule or polyatomic ion. 2. Count the number of electron domains on the central atom. 3. Determine the electron-domain geometry by applying the VSEPR model. 4. Determine the molecular geometry by considering the positions of the atoms only.

Importance of Molecular Geometry and Polarity

Molecular geometry is important in understanding the physical and chemical properties or behaviors of a substance. Molecular polarity influences physical, chemical, and biological properties.

Structural isomers

Molecules that have the same chemical formula, but different arrangements of atoms

Valence bond theory

Atoms share electrons when an atomic orbital on one atom overlaps with an atomic orbital on the other. Each of the overlapping atomic orbitals must contain a single, unpaired electron. the two electrons shared by the bonded atoms must have opposite spins.

Why do chemical bonds form according to valence bond theory?

A covalent bond forms between the two atoms if the potential energy of the resulting molecule is lower than that of the isolated atoms, so the formation of a covalent bond is exothermic.

Valence bond theory perspective to the bond angle in H2S

The central atom has 2 unpaired electrons, each resides in a 3p orbital, and each singly occupied 3p orbitals overlap with the is orbital of a hydrogen atom.

Why valence bond theory needs modification?

Valence bond theory fails to explain the bonding in many molecules. An atom must have a singly occupied atomic orbitals to form bond with another atom, so how can we explain the bonding in BeCl2?

Hybridization

Mixing atomic orbitals

Paramagnetism vs. Diamagnetism

Paramagnetic species are attracted by magnetic fields, whereas diamagnetic species are weakly repelled by them.

Molecular orbital theory

Atomic orbitals combine to form new orbitals that are the “property” of the entire molecule, rather than of the atoms forming the bonds. Electrons shared by atoms in a molecule reside in the molecular orbitals.

Bond order

number of electrons in bonding molecular orbitals − number of electrons in antibonding molecular orbitals / 2

Molecular Orbitals in Heteronuclear Diatomic Species

The atomic orbitals of the more electronegative atom are lower in energy than the corresponding atomic orbitals of the less electronegative atom. The lower-energy atomic orbital contributes more to the bonding molecular orbital; and the higher-energy atomic orbital contributes more to the antibonding molecular orbital.

Molecular geometry

The arrangement of bonded atoms in a molecule.

Valence-shell electron-pair repulsion (VSEPR) model

A model used to predict the geometry of molecules based on minimizing the electrostatic repulsion of electron pairs around a central atom.

Electron domain

The region around the central atom in which there is a high probability of finding electrons; they can be bonding pairs or lone pairs.

Electron pair.

A bonding or nonbonding pair of electrons in the valence shell of an atom.

Electron domain geometry

A region in a molecule where the electron density is concentrated.

Tetrahedral

Molecular shape of a molecule with four electron domains surrounding the central atom where all electron domains are bonding.

Trigonal Planar

Molecular shape of a molecule with three electron domains surrounding the central atom and all electron domains are bonding.

Linear

Molecular shape of a molecule with two electron domains surrounding the central atom and all electron domains are bonding.

Polar Molecule

A molecule with polar bonds that does not have symmetry and and therefore possesses a net dipole moment.

Dipole Moment

A measure of the polarity of a molecule. It is defined as the product of the magnitude of the charge $Q$ and the distance $r$ between the charges.

Dipole Moment Equation

Quantitatively expressed as: $\mu = Q \times r$

Dipole Moment Magnitude

Magnitude is typically on the order of $10^{-30}$ Coulomb-meters (C⋅m), often expressed in the unit debye (D), where $1 D = 3.336 \times 10^{-30} C⋅m$

Nonpolar Molecule

A molecule with polar bonds that cancels due to the symmetry of the molecule.

Intermolecular forces

Attractive forces between molecules.