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3 Types of Bonds Ionic Covalent Metallic
Which atoms/ions make these bonds? How do bonds form (share or electrostatics)?
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Ionic Properties? States of matter?
Ease of formation depends on ? and ? Draw Lewis dot structures to represent formation of ionic bonds (electrostatic attraction) Do NaCl Try CaCl2
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Electrostatics → Lattice Structure
Coulomb Forces very important To make lattice, try to maximize ________________ and minimize ________________
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Lattice Energy Energy to ??? Endo or exo?
What would influence lattice energy? Think Coulomb Arrange NaF, CsI, and CaO in order of increasing lattice energy. Explain your order.
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Compound Lattice Energy (kJ/mol) LiF 1030 MgCl2 2326 LiCl 834 SrCl2 2127 LiI 730 NaF 910 MgO 3795 NaCl 788 CaO 3414 NaBr 732 SrO 3217 NaI 682 KF 808 ScN 7547 KCl 701 KBr 671 CsCl 657 CsI 600
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Covalent Bonding How are these bonds made?
Properties? States of Matter? Structure-Do you expect lattice structures?
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Structure is Molecular or Network
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Lewis Dot Diagrams For each of the following, a. Draw the Lewis structure b. Does it obey octet rule? Does it have to? c. Name it CH4, H2O, N with F, BH3, PCl5, CO2, N2, CO Why can B have CN=3? Why can P expand? Why can N2 make triple? Bond length of CO vs CO2?
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Do we always have equal sharing?
Review Polarity ( charge), Dipole moment ()
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0-0.4: nonpolar covalent : slightly polar : polar > 2: ionic Which bond is more polar and draw the dipole moment? S-Cl, S-Br, Se-Cl, or Se-Br B-Cl or C-Cl
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Cl-F = 0.88 D Bond length = 1.63 Å Does the small value make sense? Which atom is expected to be -? Which +? Draw
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= Qr Q = electron charge r = bond length
Make sense? Cmpd r (Å) Pauling (D) HF 0.92 1.9 1.82 HCl 1.27 0.9 1.08 HBr 1.41 0.7 0.82 HI 1.61 0.4 0.44
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Summary Ionic M with NM High mp Brittle Lattice structure
Electroneg diff > 2.0 Ionic Solids = non-conductive Covalent NM’s only Low mp Molecular (few network solids) Polarity ( ) Some trans M salts can be covalent (next slide)
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Trans M Salts: Ionic or Cov? Depends on oxid state of Metal
MnO Mn2O7 green solid green liq mp = 1842oC fp 5.9oC What is oxid state of Mn in each cmpd? Name each cmpd. Based on Pauling scale, what is expected? Mn = 1.5; O = 3.5 Look at props, what do you think? Trend? (side note: cut off is usually +4)
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Try This Cmpd A is a yellow solid whose mp = 41oC
Cmpd B is a green solid whose mp = 2320oC Match them to Cr2O3 and OsO4
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Lewis Structures ctd. Use valence e-
Central atom: least amt or least electroneg Octet Rule (C, N, O, F) Must also consider Resonance (Draw ClO2- ) (Name of this ion?) Formal Charge least amt FC or negative FC on most electroneg atom Which resonance form is energetically most favorable?
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Try SCN- There are three resonance forms
Draw them and pick the best one Try Ozone, O3 2 or 3 resonance forms? Would you expect two different bond lengths? In reality, only get one (in between single and double). Why? Discuss resonance and partial double bond character
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Common Examples Polyatomics with O show resonance and partial bond character Examples? Benzene, C6H6 =
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Bond Enthalpy, H Bond enthalpy is the energy needed to break covalent bonds (lattice E = E to break lattice) For ex, Cl2 → 2 Cl H = 242 kJ/mol Does + value make sense? What does this # mean? Translate/sentence C-H has H = 413 kJ What is the overall energy to break up methane? CH4 → C + 4H
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Draw Lewis for O2 and H2O2 Compare the O to O bond strength in each compound. One has H=495 kJ; the other has H=146 kJ. Which is which? Which would be more reactive?
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Use Bond Enthalpies to find Hrxn
Hrxn = H bonds broken - H bonds made Ex. 2 C2H6 + 7 O2 → 4 CO2 + 6 H2O ANS: kJ Does negative make sense? Explain the # in words. Name of C2H6?
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