09 - Lone pairs take up more space than bonding electrons...

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Chapter 13 9/17/09 Lattice Energy : The change in E that takes place when separated gaseous ions are packed together to form an ionic solid; Energy of stabilization that derives from Coulombic interactions E= kQ 1 Q 2 r Ionic + Covalent Bonds Bonds that share electrons equally are called (purely) covalent bonds How uneven is the electron density distribution in a given covalent bond? Some resonance forms are more important than others Forms that involve charge separation are generally less important Theories of Bonding Lewis Dot Structures as a bonding model have deficiencies 1940: Sidgwick & Powell Concept of based e- — e- repulsions V alence S hell E lectron P air R epulsion (VSEPR) Moelcular shape is determined by pairs of electrons residing as far away from each other as possible Repulsion between lone pairs of electrons is greater than that between bonding pairs— lone pairs of electrons are more bulky
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Unformatted text preview: Lone pairs take up more space than bonding electrons Expect that heteronuclear structures will show different effects on shape based on the nature of bonding electrons 2 pairs of e- in double bonds should repel more than one pair (single bond) IF all the bonds of PF5 were the same length, there would be more electron repulsions in the equatorial interaction VSEPR 1) Electrons around a central atom with organize to minimize e- pair repulsions 2) Most prohibitive interaction is lone-pair—lone-pair 3) In structures with 90° interactions, the most favored structure is the one with the fewest 90° lone pair interactions Dipole Moments Electronegativity: e- will be shifted towards the element with the higher electronegativity Dipolar molecule: can be oriented in an electric field The nature of charge separation can be quantified by the dipole moment (mu) (mu) = q x r...
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