Lecture-13 - Chem111 Fall, 2005 51 Enough of atoms! Let's...

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Unformatted text preview: Chem111 Fall, 2005 51 Enough of atoms! Let's see how they form molecules Consider the molecules CO 2 and H 2 O O C O O H H linear bent non-polar quite polar gas at room temp. liquid at RT two double bonds two single bonds We could use the Schrdinger equation , approximations, lots of complicated mathematics, and a computer program and solve for the structures of our molecules. too expensive (both $$ and time) / we will come up with "rough" methods, based upon concepts Organization of this part of the course What are bonds? (Ionic bonds, covalent bonds, in-between) Brief review of Lewis dot structures electron bookkeeping How can we predict (accurately) the shapes of molecules? (VESPR) What does quantum mechanics tell us about bonding? (Molecular Orbitals) Lecture 13: Bonding and Molecules Ionic and Covalent bonds Electronegativity Lewis Dot Structures VESPRR (I) Chem111 Fall, 2005 52 Bonds What IS a bond? when atoms interact with one another, they can "stick" together to form a bond there are several kinds of bonds (we focus on ionic and covalent) the bonds give molecules and materials their unique properties Ionic Bond involves a transfer of an electron from one atom to another for example NaCl Na + Cl- Ionic materials usually have high melting (& boiling) points (NaCl MP = 801 o C) conduct electricity when molten or in solution are brittle solids Covalent Bond involves a sharing of electron(s) between atoms in the bond for example CO 2 O C O Covalent materials usually have lower melting (& boiling) points (CO 2 MP = -40 o C) do not conduct electricity in any form can be gas, liquid or solid at room temperature transfers an electron from sodium to chlorine Coulomb interaction between two ions 4 electrons shared in each double bond Chem111 Fall, 2005 53 Actually, these are two ends of a continuum 0% covalent 100% covalent 100% ionic 0% ionic (electron (part e- transfer (e- shared transfer) part e- sharing) equally) We will focus on diatomic molecules for a bit Ionic Bonds : occur for atoms that have different ionization energies and electron affinities one atom has a large IE and the other has a large EA Electronegativity...
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This note was uploaded on 02/08/2010 for the course CHEM 111 taught by Professor Kenney during the Spring '08 term at Case Western.

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Lecture-13 - Chem111 Fall, 2005 51 Enough of atoms! Let's...

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