Valence Shell Electron Pair Repulsion Theory VSEPR Valence Shell Electron Pair Repulsion Theory www.longview.k12.wa.us/ralong/tietjen/Chemistry/VSEPR.JAT.ppt
TEKS 7 (E) predict molecular structure for molecules with linear, trigonal planar, or tetrahedral electron pair geometries using Valence Shell Electron Pair Repulsion (VSEPR) theory.
Vocabulary: “domain” = any electron pair, or any double or triple bond is considered one domain. “lone pair” = “non-bonding pair” = “unshared pair” = any electron pair that is not involved in bonding “bonding pair” = “shared pair” = any electron pair that is involved in bonding
2 domains on central atom LINEAR 2 domains both are bonding pairs They push each other to opposite sides of center (180 apart). BeCl2
3 domains on central atom TRIGONAL PLANAR 3 domains all are bonding pairs They push each other apart equally at 120 degrees. GaF3
4 domains on central atom TETRAHEDRAL 4 domains Each repels the other equally - 109.5 - not the expected 90. Think in 3D. CH4
Steps for using VSEPR: Draw a Lewis Dot Structure. Predict the geometry around the central atom. Predict the molecular shape. … also, we can try and predict the angles between atoms.
All e- pairs push each other as far apart as possible. Shared (bonding) pairs are “stretched” between two atoms that want them. “Longer & Thinner” Unshared (non-bonding) pairs are not “stretched.” “Shorter & Thicker”
Electron Pair Repulsion 2 lone pairs require the most space & repel each other the most, resulting in the greatest distance (angle). 1 lone pair (thick) & 1 bonding pair (thin) require less space 2 bonding pairs (both thin) require the least space & repel each other the smallest distance (angle).