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2Na(s) + Cl 2 (g)  2NaCl (s)

Synthesizing an Ionic Compound. 2Na(s) + Cl 2 (g)  2NaCl (s). Explaining Salt Formation using the Born-Haber Cycle. Explaining Salt Formation using the Born-Haber Cycle. Na(s) + Cl 2  NaCl H° f = -411 kJ/mol. Na(s)  Na(g) H° f = 108 kJ/mol.

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2Na(s) + Cl 2 (g)  2NaCl (s)

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  1. Synthesizing an Ionic Compound 2Na(s) + Cl2 (g)  2NaCl (s)

  2. Explaining Salt Formation using the Born-Haber Cycle

  3. Explaining Salt Formation using the Born-Haber Cycle Na(s) + Cl2 NaCl H°f = -411 kJ/mol Na(s)  Na(g) H°f = 108 kJ/mol Cl2 Cl(g) H°f = 122 kJ/mol Na(g)  Na+(g) + e- I1 = 496 kJ/mol Cl(g) + e-  Cl-(g) E = -349 kJ/mol H = [H°f (NaCl)] -[H°f (Na+) + H°f (Cl-) + I1 + E] H = -788 kJ/mol

  4. Describing Electrostatic Attraction and Repulsion Q1Q2 E = k d E > 0 if the charges Q1 and Q2 have the same sign • Potential energy increases because the particles are repelling E < 0 if the charges Q1 and Q2 have different signs • Potential energy decreases because the particles are attracting

  5. Q1Q2 E = k d The lattice energy of NaCl is the result of all the electrostatic repulsions and attractions. Because the attractions outweigh the repulsions, the lattice energy is positive and large

  6. size depends upon nuclear charge Sizes of Ions • size depends upon numbers of electrons • size depends upon orbitals in which the outer electrons reside

  7. Within an Isoelectric Series, the higher the atomic number the smaller the ion

  8. Covalent Bonds are formed by shared pairs of electrons   H + H H H H H Single Bonds +   Cl Cl Cl Cl Cl Cl Double Bonds + +  C O  O C O O O C O Triple Bonds  + N N N N

  9. Resonance Forms O O  O O O O

  10. Exceptions to the Octet Rules • Molecules with an odd number of electrons NO contains 5 + 6 = 11 electrons. No octet can be established • Molecules in which an atom has less than an octet Though rare, these are most often encountered in compounds of Born and Beryllium F B F F

  11. Exceptions to the Octet Rules Molecules in which an atom has more than an octet This is observed in compounds constructed from period 3 elements and beyond Cl Cl P Cl Cl Cl 3s 3p 3d

  12. Strengths of Covalent Bonds Bond dissociation Energy (Bond Energy): is the enthalpy change (H) required to break a particular bond in a mole of gaseous substance (g) (g)  Cl Cl 2 Cl H = 242 kJ Bond Energies and the Enthalpy of Reactions H = (bond energies of bonds broken) -  (bond energies of bonds formed)

  13. H = (bond energies of bonds broken) -  (bond energies of bonds formed) Cl2(g) + H-CH3 H-Cl(g) + CH3Cl H = [(Cl-Cl) + 4(H-C)] - [(Cl-Cl) + 3(H-C) + (Cl-C)] H = [242 kJ+4(413 kJ)]-[431 kJ + 4(413kJ) + (328)] = -104 kJ

  14. Bond Strength and Bond Length

  15. Electronegativity and Bond Polarity “the ability of an atom in a molecule to attract electrons to itself”

  16. Electronegativity and Bond Polarity H2 : Ediff = 2.1 -2.1 = 0 Cl2 : Ediff = 3.0 - 3.0 = 0 BH3 2.1-2.0 = .1 Cl H - + Cl H HCl: Ediff = 3.0 -2.1 = 0.9 note that LiF is ionic : Ediff = 4.0 - 1.0 = 3.0

  17. Ionic Character • The bigger the electronegativity difference the more ionic character. • 1.4 has more ionic character than 1.2

  18. noble gas configurations • Cl1- • Na1+ • Cu1+ • Sn2+

  19. Isoelectronic • O2-, Cl1-, Ne, Na1+, Mg2+ • size trend

  20. energy diagram page 366

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