Unit 2 Guide: Molecular and Ionic Compound Structure and Properties

Lewis Diagram

A two-dimensional representation of a molecule showing how valence electrons are distributed among atoms as bonds or lone pairs.

Valence Electrons

Electrons in the outer shell of an atom that determine its chemical bonding properties.

Central Atom

The least electronegative atom in a molecule, often Carbon, that is surrounded by other atoms.

Octet Rule

Atoms are generally stable when they have eight electrons in their valence shell.

Incomplete Octets

Atoms like Hydrogen, Boron, and Beryllium can be stable with fewer than eight electrons.

Expanded Octets

Atoms in Period 3 and below can have more than eight electrons in their valence shell, utilizing empty d orbitals.

Resonance Structures

Equivalent Lewis structures that can describe a single molecule, indicating delocalized electrons.

Formal Charge

A calculation used to determine the most stable Lewis structure by assessing the distribution of electrons.

Electron Domain

A region of electron density around a central atom, including bonds and lone pairs.

VSEPR Theory

The Valence Shell Electron Pair Repulsion theory, which predicts the 3D geometry of molecules based on electron repulsion.

Lone Pair

An electron pair that is not involved in bonding and is localized around a single atom.

Bonding Pair

A pair of electrons that are shared between two atoms, forming a chemical bond.

Trigonal Planar

A molecular geometry with three bonding pairs and no lone pairs, resulting in 120° bond angles.

Tetrahedral

Molecular geometry with four bonding pairs and no lone pairs, resulting in approximately 109.5° bond angles.

Sigma Bond

A type of covalent bond formed by the direct overlap of atomic orbitals, allowing free rotation.

Pi Bond

A type of covalent bond formed by the side-to-side overlap of unhybridized p-orbitals, which restricts rotation.

Hybridization

The mixing of atomic orbitals to form new hybrid orbitals for bonding.

Common Mistakes

Frequent errors in drawing Lewis structures and predicting molecular geometry.

Molecular Geometry

The shape of a molecule as determined by the arrangement of only the bonding pairs.

Electron Geometry

The shape of a molecule considering both bonding and lone pairs.

Bond Order

The number of bonds between two atoms, which can be calculated using resonance structures.

Approximate Bond Angles

Predicted angles between bonds in specific geometries, modified by lone pair repulsion.

Formal Charge Calculation Formula

FC = Valence Electrons - Nonbonding Electrons - (Bonding Electrons / 2)