CHEMICAL BONDING - Chemical Bonding Petrucci, Harwood and...

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•1 CHEM 1000 3.0 Chemical Bonding I 1 Chemical Bonding • Petrucci, Harwood and Herring: Chapters 10 and 11 • Aims: – 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 CHEM 1000 3.0 Chemical Bonding I 2 Chemical Bonding • The most important concepts here are: – Electrons, particularly valence electrons play a fundamental role in chemical bonding. – When elements combine to produce compounds they are attempting to achieve a valence shell like a noble gas CHEM 1000 3.0 Chemical Bonding I 3 Chemical Bonding • The driving force for the production of chemical bonds is the need for an atom to complete a valence shell (usually 8 electrons) – Often 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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•2 CHEM 1000 3.0 Chemical Bonding I 4 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 CHEM 1000 3.0 Chemical Bonding I 5 Lewis Structures • These are the combination of Lewis symbols that represents the sharing or transfer of electrons in a molecule – Examples – Ionic bond – Covalent bond Na + Cl [Na] + [ Cl ] - x x H + Cl H Cl x x CHEM 1000 3.0 Chemical Bonding I 6 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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•3 CHEM 1000 3.0 Chemical Bonding I 7 Ionic Compounds CHEM 1000 3.0 Chemical Bonding I 8 Covalent Compounds • Here electrons are shared between two atoms. – (May actually be more than just a couple of shared electrons) – The electrons spend “time” around each atom in the covalent bond – The overall effect is that each atom has “more” (usually a full shell of) valence electrons. CHEM 1000 3.0 Chemical Bonding I 9 Covalent Compounds • Examples – 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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CHEMICAL BONDING - Chemical Bonding Petrucci, Harwood and...

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