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Published byAmy York Modified over 9 years ago
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What is polarity? Focus on covalent bonds Contributes to the properties of chemical compounds Based on electronegativity difference between atoms within chemical bonds
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Chose your polarity 1) Nonpolar Covalent small to same electronegativity difference Occurs among same or similar atoms bonded together EQUAL sharing of electrons, equal distribution of electron density 2) Polar Covalent difference in electronegativity Most electronegative atom pulls electrons towards it UNEQUAL sharing of electrons, electron density displaced toward electronegative atom
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Polar Covalent Bonds
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Example 1: Arrange the following bonds in order of DECREASING polarity. Br—ClH--Cl Cl—ClI--Cl Cl--F
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Partial Charges Exist in polar covalent molecules Demonstrates tendency of one end to be “slightly” negative or positive NO charge on the whole molecule
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Example 1: H 2 O
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Example 2: HCl
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Example 3: PH 3
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Formal Charges Difference between # of valence electrons present in an atom NOT in chemical bond and # of valence electrons present in an atom WITH a chemical bond Not actual charges in covalent molecule Neutral molecules = 0 formal charge Polyatomic/charged molecule = net charge Valence Electrons in atom involved in chemical bond Lone-pair electrons around atom ½ electrons in a chemical bond
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Formal Charges (cont.) Formal Charge = #valence electrons in free atom - #lone pair electrons around bound atom – ½ (# of electrons present in bond with atom)
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Example 1: Which Lewis structure is more likely???
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Resonance Some molecules or ions have more than one possible Lewis Structure Structures ONLY vary in electron distribution Resonance hybrid A mix/hybrid of all possible Lewis structures True molecule/ion structure ** Draw all resonance structures and connect with double arrow— resonance hybrid is a blend **
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Resonance (cont.) Delocalized Electrons Electrons are not restricted to where they can “hang out” Electrons distribute among several atoms Seen with resonance as electron distribution varies Localized Electrons Electron distribution does NOT vary Electrons stay in a specific region between atoms No resonance
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Example 1: Draw 3 Lewis structures for SO 3 and describe how the resonance hybrid relates to all 3.
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Example 2: Draw 3 Lewis structures for NO 3 - and describe how the resonance hybrid relates to all 3.
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Homework Read pp. 351-353, 357-360 Problems pp. 381-382, #41, 42, 45, 46, 47, 49, and 51
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