4_ChemicalBonding(S)

4_ChemicalBonding(S) - Chemical Bonding Petrucci, Herring...

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CHEM 1000 3.0 Chemical Bonding 1 Chemical Bonding • Petrucci, Herring Madura and Bissonnette : Chapters 10 and 11 •A i m s : – To look at bonding and possible shapes of molecules • We will mainly do this through Lewis structures – To look at ionic and covalent bonds – Use valence shell electronic structure to predict shapes of molecules
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CHEM 1000 3.0 Chemical Bonding 2 Problem set Chapter 10 questions 3, 4, 11, 17, 18, 21, 22b), 59, 62, 141 Chapter 11 questions 7, 13, 17
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CHEM 1000 3.0 Chemical Bonding 3 Chemical Bonding • Lewis Theory: – Electrons, particularly valence electrons play a fundamental role in chemical bonding. – When elements combine to produce compounds they are attempting to achieve a full valence shell (usually 8 electrons)
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CHEM 1000 3.0 Chemical Bonding 4 Chemical Bonding • Lewis Theory: – Electrons can be transferred from one atom to another to make ions. The atoms are then held together by coulombic forces in an ionic bond – More often the only way an atom can gain electrons is by sharing . This sharing produces a covalent bond
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CHEM 1000 3.0 Chemical Bonding 5 Lewis Symbols • This is a way of representing the valence electrons in an element – It does not include the inner shell electrons – It does not include the spin of an electron – e.g. Si ([Ne]3s 2 3p 2 ) – N ([He]2s 2 2p 3 ) Si N
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CHEM 1000 3.0 Chemical Bonding 6 Lewis Structures • These are the combination of Lewis symbols that represents the sharing or transfer of electrons in a molecule – Ionic bonding examples ( electron transfer) Na + Cl [Na] + [ Cl ] - x x Mg + 2 Cl [Mg] 2+ 2 [ Cl ] - x x x
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CHEM 1000 3.0 Chemical Bonding 7 Ionic Compounds • We don’t usually see isolated ionic compounds – Normally they are in crystals where one anion (negative) is attached to several cations (positive) and vice versa. Electrical neutrality means the total number of each ion is the same.
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CHEM 1000 3.0 Chemical Bonding 8 Ionic Compounds
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CHEM 1000 3.0 Chemical Bonding 9 Lewis Structures • These are the combination of Lewis symbols that represents the sharing or transfer of electrons in a molecule – Covalent bonding example (sharing) H + Cl H Cl x x
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CHEM 1000 3.0 Chemical Bonding 10 Covalent Compounds • Here electrons are shared between two atoms. – Why? Because the energy cost of making the ions is too high – Could be more than just a couple of shared electrons – The electrons are associated with each atom in the covalent bond – The overall effect is that each atom has “more” (usually a full shell of) valence electrons.
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CHEM 1000 3.0 Chemical Bonding 11 Covalent Compounds •E x a m p l e s – Single covalent bond HCl Note that there are 6 electrons around the Cl that are not involved in bonding. It is normal to talk about these as lone pairs , in contrast to bond pairs Lone pairs Bond pair H Cl H Cl
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CHEM 1000 3.0 Chemical Bonding 12 Coordinate Covalent Bonds Bonds do not have to come from equal sharing of electrons In NH 4 + there are 8 electrons around the N, but it has 5 to start with. Hence the hydrogens only contribute 3 of the 8 bonding electrons.
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CHEM 1000 3.0 Chemical Bonding 13
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This note was uploaded on 12/09/2010 for the course CHEM CHEM 1000 taught by Professor Marzad during the Fall '09 term at York University.

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4_ChemicalBonding(S) - Chemical Bonding Petrucci, Herring...

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