Chapter 9 - Molecular Geometries and Bonding Theories

Chapter 9 - Molecular Geometries and Bonding Theories -...

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1 Chapter 9 Chapter 9 Molecular Geometries Molecular Geometries and Bonding Theories and Bonding Theories
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2 Review: Writing Lewis Structures Review: Writing Lewis Structures 1. Find the sum of valence electrons of all atoms in the polyatomic ion or molecule. If it is an anion, add one electron for each negative charge. If it is a cation, subtract one electron for each positive charge. 2. The central atom is the least electronegative element that isn’t hydrogen. Connect the outer atoms to it by single bonds. 3. Fill the octets of the outer atoms. 4. Fill the octet of the central atom. 5. If you run out of electrons before the central atom has an octet - form multiple bonds until it does. Then assign formal charges. – For each atom, count the electrons in lone pairs and half the electrons it shares with other atoms. – Subtract that from the number of valence electrons for that atom: The difference is its formal charge. The best Lewis structure… – …is the one with the fewest charges. – …puts a negative charge on the most electronegative atom. Molecular Shapes Molecular Shapes •The shape o f a molecule plays an important role in its reactivity. • By noting the number of bonding and nonbonding
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3 What Determines the What Determines the Shape of a Molecule? Shape of a Molecule? • Simply put, electron pairs, whether they be bonding or nonbonding, repel each other. • By assuming the electron pairs are placed as far as possible from each other , we can predict the shape of the molecule. Electron Domains Electron Domains • We can refer to the electron pairs as electron domains . •In a double or triple bond, all electrons shared between those two atoms are on the same side of the central atom; therefore, they count as one electron domain . • This molecule has four electron
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4 Valence Shell Electron Pair Valence Shell Electron Pair Repulsion Theory (VSEPR) Repulsion Theory (VSEPR) “The best arrangement of a given number of electron domains is the one that minimizes the repulsions among them.” Vsepr.mov Electron Electron -Domain Domain Geometries Geometries These are the electron-domain geometries for two through six electron domains around a central atom.
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Electron Electron -Domain Geometries Domain Geometries • All one must do is count the number of electron domains in the Lewis structure. • The geometry will be that which corresponds to that number of electron domains. Note: the electron domain geometry and molecular geometry may not be the same. Molecular Geometries Molecular Geometries • The electron-domain geometry is often not the shape of the molecule, however. • The molecular geometry is that defined by the
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Chapter 9 - Molecular Geometries and Bonding Theories -...

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