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Energy of Bond Formation

Bond Energies. Energy of Bond Formation. Every reaction has an associated quantity of energy . Every reaction has an associated quantity of energy True for both chemical or physical changes. Every reaction has an associated quantity of energy True for both chemical or physical changes

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Energy of Bond Formation

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  1. Bond Energies Energy of Bond Formation

  2. Every reaction has an associated quantity of energy

  3. Every reaction has an associated quantity of energy • True for both chemical or physical changes

  4. Every reaction has an associated quantity of energy • True for both chemical or physical changes • But chemical bonds form for the purpose of lowering the potential energy associated with an atom

  5. For all elements except the noble gases…….

  6. For all elements except the noble gases……. • Isolated atoms are not stable

  7. For all elements except the noble gases……. • Isolated atoms are not stable • Attractive forces that occur when bonding to another atoms produces a more stable arrangement than single atoms

  8. Consider the H2 example

  9. Consider the H2 example • The diatomic molecule is most stable

  10. Consider the H2 example • The diatomic molecule is most stable • As the lone atoms approach, interaction starts e + + e

  11. Consider the H2 example • The protons are attracted to the electrons e + + e

  12. Consider the H2 example • The protons are attracted to the electrons • At some distance e-repel/ protons repel e + + e

  13. Consider the H2 example • The attractive and repulsion forces balance e + + e

  14. Consider the H2 example • The attractive and repulsion forces balance • This is when the 2 atoms are at a minimum potential energy e + + e

  15. Continuing with the H2 Example

  16. Continuing with the H2 Example • Bond energy is associated with bond length.

  17. Bond energy is associated with bond length. H-H

  18. Bond energy is associated with bond length. H-H 75 picometer

  19. Bond energy is associated with bond length. H-H 75 picometer 436 kj/mol

  20. Bond energy is associated with bond length. H-H 75 picometer 436 kj/mol • Recall the inverse relationship between bond length and bond energy

  21. Bond energy is associated with bond length. H-H 75 picometer 436 kj/mol • Recall the inverse relationship between bond length and bond energy • For H2 ….Fairly strong bond—energy to break is fairly high

  22. Consider other bond energies

  23. Consider other bond energies This is the energy released when the bond forms (-159 for F-F) ……..or The energy required to break the bond (+159 for F-F)

  24. Consider Ionic Compounds

  25. Consider Ionic Compounds • Not molecules

  26. Consider Ionic Compounds • Not molecules • Have an arrangement of several ions all interacting with each other.

  27. Consider Ionic Compounds • Not molecules • Have an arrangement of several ions all interacting with each other. • The solid is a regular arranged pattern of ions called a crystal lattice.

  28. LiF…….An ionic compound between lithium and fluorine

  29. LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas 1. Li (s)  Li (g) +161 kJ/mol

  30. LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+ (g)+e- +520kJ/mol

  31. LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) F molecules need to be broken into atoms 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+(g)+e- +520kJ/mol 3. 1/2F2 (g)  F (g) +77 kJ/mol

  32. LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) F molecules need to be broken into atoms Form F ions 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+ (g)+e- +520kJ/mol 3. 1/2F2 (g)  F (g) +77 kJ/mol 4. F (g) + e-  F- (g) -328 kJ/mol

  33. LiF…….An ionic compound between lithium and fluorine Li (s) + ½ F2 (g)  LiF (s) Li must be converted to a gas Li must be ionized (ionization energy) F molecules need to be broken into atoms Form F ions (electron affinity) The ions are highly attracted to each other…Lattice energy 1. Li (s)  Li (g) +161 kJ/mol 2. Li (g)  Li+ (g)+e- +520kJ/mol 3. 1/2F2 (g)  F (g) +77 kJ/mol 4. F (g) + e-  F- (g) -328 kJ/mol 5. Li+ + F-  LiF -1047kJ/mol

  34. An ionic compound forms between a metal and a nonmetal • Net change: kj/mol

  35. An ionic compound forms between a metal and a nonmetal • Net change: kj/mol • 1. 161 • 2. 520 • 3. 77 • 4. -328 • 5. -1047 - 617 kJ/mol of LiF formed

  36. An ionic compound forms between a metal and a nonmetal • The solid formed is a regular arranged pattern of ions called a crystal lattice • Net change: kj/mol • 1. 161 • 2. 520 • 3. 77 • 4. -328 • 5. -1047 - 617 kJ/mol of LiF formed

  37. An ionic compound forms between a metal and a nonmetal • The solid formed is a regular arranged pattern of ions called a crystal lattice • Lattice energy of LiF is -1047 kJ/mol • Net change: kj/mol • 1. 161 • 2. 520 • 3. 77 • 4. -328 • 5. -1047 - 617 kJ/mol of LiF formed

  38. As LiF (or another ionic compound dissolves in water………….

  39. As LiF (or another ionic compound dissolves in water…………. • Energy must be released to pull ions apart

  40. As LiF (or another ionic compound dissolves in water…………. • Energy must be released to pull ions apart • The quantity of energy released must be > or = to the lattice energy

  41. As LiF (or another ionic compound dissolves in water…………. • Energy must be released to pull ions apart • The quantity of energy released must be > or = to the lattice energy • Energy of hydration

  42. Lattice Energies of Alkali Metals Halides (kJ/mol) F-Cl-Br-I- • Li+1047 853 807 757Na+923 787 747 704 • K+821 715 682 649 Rb+785 689 660 630 Cs+740 659 631 604

  43. Lattice energy for LiF is -1047 kJ/mol….it dissolves in water • Lattice Energies of Alkali Metals Halides (kJ/mol) F-Cl-Br-I- • Li+1047 853 807 757Na+923 787 747 704 • K+821 715 682 649 Rb+785 689 660 630 Cs+740 659 631 604

  44. Lattice energy for LiF is -1047 kJ/mol….it dissolves in water • Lattice energy for MgO is -3916 kJ/mol… it does not dissolve in water • Lattice Energies of Alkali Metals Halides (kJ/mol) F-Cl-Br-I- • Li+1047 853 807 757Na+923 787 747 704 • K+821 715 682 649 Rb+785 689 660 630 Cs+740 659 631 604

  45. Lattice energy for LiF is -1047 kJ/mol….it dissolves in water • Lattice energy for MgO is -3916 kJ/mol… it does not dissolve in water • Lattice energy for NaF • -923kJ/mol • Lattice Energies of Alkali Metals Halides (kJ/mol) F-Cl-Br-I- • Li+1047 853 807 757Na+923 787 747 704 • K+821 715 682 649 Rb+785 689 660 630 Cs+740 659 631 604

  46. Hydration of ion..dissolving • Requires and interaction with the polar water molecule • General rule of solubility…”Like dissolves like” • Nonpolar molecules require nonpolar solvents

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