4 3 VSEPR THEORY valenceshellelectronpairrepulsion theory shape of

4. 3 VSEPR THEORY valence-shell-electron-pairrepulsion theory

• shape of molecules – Early studies used techniques such as crystallography, using microscopes and polarimeters, X-ray and other spectrographic techniques

VSEPR • 1957 that Australian Ronald Nyholm and Englishman Ron Gillespie created a much simpler theory for describing, explaining, and predicting the stereochemistry of chemical elements and compounds

Theory • Only the valence shell electrons of the central atom(s) are important for molecular shape. • Valence shell electrons are paired or will be paired in a molecule or polyatomic ion. • Bonded pairs of electrons and lone pairs of electrons are treated approximately equally. • Valence shell electron pairs repel each other electrostatically. • The molecular shape is determined by the positions of the electron pairs when they are a maximum distance apart (with the lowest repulsion possible).

Linear • General Formula - AX 2 • 2 BP, 0 LP

Bent (V-shaped) • General Formula. AX 2 E 2 • 2 BP, 2 LP

Trigonal Planar • General Formula-AX 3 • 3 BP

Tetrahedral • General Formula-AX 4 • 4 BP

Trigonal Pyramidal • General Formula-AX 3 E • 3 BP, 1 LP

Trigonal bipyramidal • General Formula-AX 5 • 5 BP

See. Saw • General Formula-AX 4 E • 4 BP, 1 LP

Octahedral • General Formula-AX 6 • 6 BP

Square Pyramidal • General Formula. AX 5 E • 5 BP, 1 LP

Square Planar • General Formula. AX 4 E 2 • 4 BP, 2 LP

How to do VSEPR • Draw the Lewis diagram structure • Place central atom electrons accordingly to minimize repulsion • Place atoms bonded to central atom • Determine the name of the structure from the position of atoms and lone pairs

Determine the shape of methane

More than one Central Atom • Predict the structure around each central atom that would minimize electric repulsion

Work • Pg. 216 # 1 -8