Chapter8_2 - 10/30/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307...

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Unformatted text preview: 10/30/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307 Chapter VIII Bonding and Molecular Structure 2 Exceptions to the Octet Rule Certain elements can violate the octet rule. Boron may form stable compounds with only __ valence electrons. Compounds in the ___ period and beyond can have more than ___ electrons. BF 3 BF 3 SF 4 SF 4 3 Exceptions to the Octet Rule Central atom = _____________ Valence electrons = __________ or electron pairs = __________ Assemble dot structure The B atom has a share in only 6 pairs of electrons (or 3 pairs). B atom in many molecules is electron deficient. The B atom has a share in only 6 pairs of electrons (or 3 pairs). B atom in many molecules is electron deficient. Boron trifluoride (BF 3 ) 10/30/2011 2 4 Exceptions to the Octet Rule Central atom = Valence electrons = ___ or ___ pairs. Form sigma bonds and distribute electron pairs. 5 pairs around the S atom. A common occurrence outside the 2nd period. 5 pairs around the S atom. A common occurrence outside the 2nd period. Sulfur tetrafluoride (SF 4 ) 5 Exceptions to the Octet Rule There are three classes of exceptions to the octet rule: 1.Molecules with an _____ number of electrons. 2. Molecules in which one atom has _______________________ 3. Molecules in which one atom has ________________________ 6 Odd Numbers of Electrons Examples: Examples: Generally molecules such as ClO 2 , NO, and NO 2 have an odd number of electrons. NO (nitrogen monoxide) Available electrons = 11 There must be an odd electron! Molecular Orbital Theory Molecular Orbital Theory will explain why NO is stable later. N O N O 11 5.5...? 2 or 10/30/2011 3 7 Incomplete Octet Relatively rare. Molecules with less than an octet are typical for compounds of Groups 1A, 2A, and 3A Most typical example is BH 3 . Available Electrons Available Electrons = 3 + 3(1) = 6 B H H H There are only __ electrons on the central atom. Hydrogen may only form one bond. The formal charges (________) support the drawn structure. 8 Central Atoms that Exceed the Octet Rule Atoms from the 3 rd period onwards can accommodate _______ than an octet. Beyond the third period, the ___-orbitals are low enough in energy to participate in bonding and accept the extra electron density. Example Example : BrF 3 Available Electrons = 7 + 3(7) = 28 Each fluorine atom can only share one electron. What does this mean?? 9 Central Atoms that Exceed the Octet Rule Bromine has 7 valence electrons (4s 2 4p 5 ) Fluorine also has 7 (2s 2 2p 5 ) BrF 3 Br has the lowest electronegativity so it will be the ___________ ___________ in the molecule. Each F shares one electron to complete an octet. There are There are ____ ____ total electrons in total electrons in the Br valence the Br valence Br F F 10/30/2011 4 10 Central Atoms that Exceed the Octet Rule 11 Molecular Shapes Lewis structures tell us how atoms are connected in a molecule: bonds (bp) & lone pairs (lp)...
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Chapter8_2 - 10/30/2011 1 1 CHEMISTRY 1307 CHEMISTRY 1307...

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