Lewis Symbols and the Octet Rule Electron Dot Symbols convenient way of showing the valence electrons of atoms. Consists of the chemical symbol and one dot for each of the valence electrons

Lewis Symbols Examples lithium electron configuration: 1s 2 2s 1 Lewis Symbol: Li boron electron configuration: 1s 2 2s 2 2p 1 Lewis Symbol: B....

Octet Rule Many atoms undergo reactions to end up with eight valence electrons as the Noble Gases

Covalent Bonding A chemical bond formed by sharing a pair of electrons Atoms may also complete octets by sharing electrons

Covalent Bonding Lewis Structures structural formulas that include electron dots

Resonance Structures Two or more Lewis structures with the same arrangement of atoms and, the same number of electron pairs, but different positions for the electrons

The Shapes of Molecules Valence Shell Electron Pair Repulsion (VSEPR) model : - predicting a molecule’s shape from the number of bonds and lone pairs of electrons surrounding individual atom

The Shapes of Molecules VSEPR Rules: 1. Draw Lewis Structure - identify atom of interest Cl Cl C Cl Cl

VSEPR Rules: 2. Count the number of electron charge clouds surrounding the atom of interest. i.e. The total number of bonds and lone pairs

VSEPR Rules: 3. Predict molecular shape by assuming charge clouds orient in space as far apart as possible

Electronic Geometry The arrangement of the charge clouds around the central atom

Molecular Geometry The arrangement of atoms around the central atom.

Molecular Shapes Two Charge Clouds: 1. Charge clouds will be on opposite sides of central atom - separated by 180 o 2. Yields linear electronic and molecular geometries

Molecular Shapes Three Charge Clouds: 1. Charge clouds will arrange themselves at the corners of an equilateral triangle o apart 2. Yields a planar triangular electronic geometry

Molecular Shapes N.B. Three charge clouds can yield either planar triangular or bent molecular geometries

Molecular Shapes Four Charge Clouds: 1. Charge clouds are oriented toward the corners of tetrahedron o apart 2. Forms tetrahedral electronic geometry

Molecular Shapes N.B. Four charge clouds can yield: 1. Tetrahedral molecular geometry 2. Pyramidal molecular geometry 3. Bent molecular geometry

Molecular Shapes Effect of Lone Pairs: - lone pairs on central atom effect angles between bonding pairs of electrons.

VSEPR Rules: Charge Clouds: 1. Single bonds 2. Multiple bonds 3. Lone pairs