General Chemistry I: Molecular Geometry and Bonding Theories

Flashcards covering key vocabulary terms related to molecular geometry and bonding theories, including VSEPR model, hybrid orbitals, sigma and pi bonds, and molecular orbital theory.

Molecular Geometry

The general shape of a molecule, as determined by the relative positions of the atomic nuclei.

Valence-Shell Electron-Pair Repulsion (VSEPR) Model

A model that predicts the shape of a molecule by assuming electron pairs (bonding and nonbonding) are placed as far as possible from each other to minimize repulsion.

Electron Domain

The directions to which electrons point, whether there is one or more electron pairs pointing in that direction.

Linear Electron Domain Geometry

An electron-domain geometry with two electron domains, resulting in a 180° bond angle.

Trigonal Planar Electron Domain Geometry

An electron-domain geometry with three electron domains, resulting in 120° bond angles.

Tetrahedral Electron Domain Geometry

An electron-domain geometry with four electron domains, resulting in 109.5° bond angles.

Trigonal Bipyramidal Electron Domain Geometry

An electron-domain geometry with five electron domains, resulting in 90° and 120° bond angles.

Octahedral Electron Domain Geometry

An electron-domain geometry with six electron domains, resulting in 90° bond angles.

Nonbonding Pairs

Electron pairs that are physically larger than bonding pairs and exert greater repulsions, tending to compress bond angles.

Multiple Bonds

Double and triple bonds that have larger electron domains and exert greater repulsive force than single bonds, making their bond angles greater.

Hypervalent Molecules

Molecules in which central atoms expand beyond the octet rule, forming more than four bonds or having more than four electron domains.

Axial Positions (Trigonal Bipyramidal)

The positions in a trigonal bipyramidal geometry that are perpendicular to the equilateral plane.

Equatorial Positions (Trigonal Bipyramidal)

The positions in a trigonal bipyramidal geometry that lie in the equilateral plane; lone pairs typically occupy these positions.

Dipole Moment

A measure of the polarity of a molecule, arising from the unequal sharing of electrons in chemical bonds.

Polar Molecule

A molecule where the average positions of positive (δ+) and negative (δ-) charges do not coincide, resulting in an overall dipole moment.

Nonpolar Molecule

A molecule where equal and oppositely directed bond dipoles cancel out, or there are no polar bonds, resulting in a zero overall dipole moment.

Valence-Bond Theory

A theory describing a covalent bond as the result of the overlap of atomic orbitals, where electrons of two atoms occupy the same space with opposite spins.

Hybrid Orbitals

New orbitals of equal energy (degenerate) formed by the 'mixing' of atomic orbitals.

sp Hybridization

The mixing of one s orbital and one p orbital to form two degenerate sp hybrid orbitals, resulting in a linear geometry.

sp2 Hybridization

The mixing of one s orbital and two p orbitals to form three degenerate sp2 hybrid orbitals, resulting in a trigonal planar geometry.

sp3 Hybridization

The mixing of one s orbital and three p orbitals to form four degenerate sp3 hybrid orbitals, resulting in a tetrahedral geometry.

Sigma (σ) Bond

A type of covalent bond formed by the head-to-head overlap of atomic orbitals, occurring in all single bonds and as one bond in multiple bonds.

Pi (π) Bond

A type of covalent bond formed by the side-to-side overlap of parallel p orbitals, found in multiple bonds in addition to a sigma bond.

Localized Electrons

Bonding electrons (σ or π) that are specifically shared between only two atoms.

Delocalized Electrons

Electrons (often π electrons) that are shared by multiple atoms across an entire molecule, which often occurs in molecules with resonance structures like benzene.

Molecular Orbital (MO) Theory

A theory describing molecular orbitals as having characteristics like atomic orbitals, formed by the combination of atomic orbitals, and capable of holding a maximum of two electrons with opposite spins.

Bonding Orbitals

Molecular orbitals formed by the constructive combination (adding) of atomic orbitals, concentrating electron density between nuclei and thus lower in energy.

Antibonding Orbitals

Molecular orbitals formed by the destructive combination (subtracting) of atomic orbitals, having zero electron density between nuclei (a nodal plane) and thus higher in energy.

Bond Order

A measure of the number of bonds between two atoms in a molecule, calculated as half the difference between the number of electrons in bonding and antibonding orbitals.

MO Diagram

An energy-level diagram showing how atomic orbitals combine to give molecular orbitals in a molecule.

Diamagnetism

The property of a substance where all electrons in every orbital are spin-paired, causing the substance to be weakly repelled by a magnetic field.

Paramagnetism

The property of a substance due to the presence of one or more unpaired electrons in an orbital, causing the substance to be attracted to a magnetic field.