# Lecture 13 - Topics for the day Administrative stuff...

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Topics for the day Administrative stuff Lattice energy Dipole moments for polyatomic molecules Localized electron bonding model Lewis dot structures Administrative stuff My ofFce hours today (Wednesday 3:30 - 4:30 pm) will be covered by Susan in my ofFce (WEL 3.153) if you speciFcally wanted to meet me, email me to set up an alternative meeting time. ALEKS obsession with Math and Measurement (Units)? fundamental skills you need to do the harder questions once you have them, it won’t ask anymore Error Correction Cations are larger than their parents, and Anions are smaller than their parents. Last time I said this: Error correction I corrected myself in class, but forgot to correct the online lecture notes. Sorry. Cations are SMALLER than their parents Mg Mg + r = 1.60 r = 0.65 Cl Cl r = 1.81 r = 0.99 and Anions are LARGER than their parents. 1 2 3

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Where were we? Attraction between two oppositely charged particles, such as those connected by an ionic bond can be understood using Coulomb’s Law . F q 1 q 2 r The charge on common ions can be predicted from their electron conFguration – stable ions have Flled valence shells. A stable molecule forms with a distance between the atoms (bond length) that gives the lowest possible energy, balancing the negative attraction and positive repulsion that the atoms feel. Molecules can be ionic ( Δ EN > ~1.3), nonpolar covalent ( Δ EN = 0), or polar covalent ( Δ EN < ~1.3). If there is a difference in charge between two ends of a bond, that bond is polar and it has a dipole moment , μ . Lattice Energy We know we can use Coulomb’s law to calculate the energy of interaction of two isolated charged atoms forming an ionic bond. The observed binding energy in an ionic solid is even higher. In the solid phase, the ions are bound even more strongly due to multi-ion interactions, which increase ionic character. Look more closely at this plot of % ionic character. This plot is for gas phase molecules. There are no 100% ionic character molecules in the gas phase. Extra stability is gained by surrounding each ion with many others of the opposite charge. The majority of ionic compounds formed by an alkali metal and a
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Lecture 13 - Topics for the day Administrative stuff...

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