Part 5 : VSEPR THEORY “Valence Shell Electron Pair Repulsion Theory”

COVALENT BONDING AND VSEPR • Part 5: VSEPR THEORY • “Valence Shell Electron Pair Repulsion Theory”

Objectives • -Explain VSEPR Theory • -Use VSEPR to predict shapes of molecules

Determining Shape • Each molecule has a different Dot Structure and shape which determines its properties • Shape is dependent on how many electron pairs surround the central atom • Some of the pairs are “bonding pairs” and some are “lone pairs”

VSEPR Theory • All pairs of electrons try to get as far apart as possible (like charges repel) • This “spreading out” of electron pairs creates certain bonding angles and shapes that differ from molecule to molecule

Domains • Each number of items a central element has (lone pair or bonded atom) is referred to as a “domain” • We are going to discuss these different molecules by the number of domains they have

2 Domains • Ex.) BeCl2, CO2 • 2 domains: 2 bonded atoms, 0 lone pairs • Shape = “linear” • Be does this and does not follow octet rule!

3 Domains • Ex.) BF3, BCl3 • 3 domains: 3 bonded atoms, 0 lone pairs • Shape = “trigonalplanar” or “triangular planar” • 120 degree angles • Only Boron does this! • Central atom does not follow octet rule

3 Domains • Ex.) SO2 • 3 domains: 2 bonded atoms, 1 lone pair • The 2 bonded atoms are pushed apart by 3rd pair (not seen) • Shape = “bent” due to repulsion of lone pair

4 Domains • CH4 • 4 domains: 4 bonded atoms, 0 lone pairs • All angles are 109 degrees apart • Shape: “tetrahedral”

4 Domains • NH3 , PCl3 • 4 domains: 3 bonded atoms, 1 lone pair • 109 degrees • Shape: “trigonal pyramidal”

Tetrahedral vs. Trigonal pyramidal TrigonalPyramidal Molecular Shape Tetrahedral Molecular Shape

4 Domains • Ex.) H2O • 4 domains: 2 bonded atoms, 2 lone pairs • Shape: “bent”

4Domain • Ex.) HF • Fluorine is central • 4 domains: 1 bonded atom and 3 lone pairs • Shape: “linear”

5 Domains • Ex.) PCl5 • 5 domains: 5 bonded atoms, 0 lone pairs • Shape: “trigonalbipyramidal”

5 Domains • Ex.) SF4 • 5 domains: 4 bonded atoms, 1 lone pair • Shape: “seesaw”

5 Domains • Ex.) ClF3, BrF3 • 5 domains: 3 bonded atoms, 2 lone pairs • Shape: “T-shaped”

5 Domains • Ex.) XeF2 • 5 domains: 2 bonded atoms, 3 lone pairs • Shape: “linear”

5 Domains 4 atoms, 1 lone pair 5 atoms, 0 lone pairs 3 atoms, 2 lone pairs 2 atoms, 3 lone pairs

6 Domains • Ex.) SF6 • 6 domains: 6 bonded atoms,0 lone pairs • All angles 90 degree • Shape: “octahedral”

6 Domains • Ex.) BrF5 • 6 domains: 5 bonded atoms, 1 lone pair • Shape: “square pyramidal”

6 Domains • Ex.) XeF4 • 6 domains: 4 bonded atoms, 2 lone pairs • Shape: “square planar”

6 Domains 6 bonded atoms, 0 lone pairs 5 bonded atoms, 1 lone pair 4 bonded atoms, 2 lone pairs

Steps for using VSEPR: 1. Draw a Lewis Dot Structure 2. Predict the geometry around the central atom 3. Predict the molecular shape—how many domains are there? Use the chart and examples! … also, we can try and predict the angles between atoms.

All e- pairs push each other as far apart as possible • Shared (bonded) 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 most, resulting in the greatest distance (angle) • 1 lone pair (thick) & 1 bonding pair (thin) require less space • 2 bonding pairs between atoms (thin lines) and repel each other the smallest distance (angle).

Objectives • -Explain VSEPR Theory • -Use VSEPR to predict shapes of molecules

Part 5 : VSEPR THEORY “Valence Shell Electron Pair Repulsion Theory”