Bonding - Ionic and Covalent Bonding Chapter 9 Contents...

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Ionic and Covalent Bonding Chapter 9
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11/01/11 18:05 Dr. A. Gökmen, METU 2 Contents Ionic Bonds Structure of ionic compounds, energy of ionic bonds, Lattice energy Electron configurations of ions, ions of main group elements, polyatomic ions, transition metal ions Covalent Bonds Polar covalent bonds; electronegativity Lewis electron-dot formulas Delecolized bonding; resonans Formal charge and Lewis formulas Bond length and bond order Bond energy
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11/01/11 18:05 Dr. A. Gökmen, METU 3 Ionic Bonds An ionic bond is a chemical bond formed by the electrostatic attraction between positive and negative ions. An atom that loses an electron becomes a positive ion, cation, and the atom that gains electrons becomes an anion, negative ion. Oppositely charged ions attract each other and gather together to form ionic solid.
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11/01/11 18:05 Dr. A. Gökmen, METU 4 Formation of ionic bonds Transfering an electron from valence shell of Na atom to the valence shell of Cl atom: Na([Ne]3s 1 ) + Cl([Ne]3s 2 3p 5 Na + ([Ne] + Cl - [Ar] The ions formed after electron transfer from Na to Cl are extra stable due to noble gas structure. In NaCl crystal each ion attracts six oppositely charged ion. Na + ion is surrouded by six Cl - ions and vice versa.
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11/01/11 18:05 Dr. A. Gökmen, METU 5 Energy Involved in Ionic Bonding A(s) + B(s) AB(s) Substances atomizes, A(s) A(g), B(s) B(g), H>0 Electron transfer from one atom to other; formation of oppositely charged ions, A A + + e - ionization energy H>0 B + e - B - electron affinity H<0 Formation of ionic bond between ions; A + + B - AB(s) lattice energy H<0
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11/01/11 18:05 Dr. A. Gökmen, METU 6 Electrostatic Bonding and Coulomb Energy Energy of attraction between oppositely charged ions can be estimated from Coulomb law; + - r Q kQ E 2 1 = k=8.99x10 9 J.m/C 2 (C is coulomb) Q 1 , Q 2 are charges on ions R is the distance between ions. r E 1/r
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11/01/11 18:05 Dr. A. Gökmen, METU 7 Coulomb Energy between Na + and Cl - What is the electrostatic bonding energy between Na + and Cl - in NaCl crystal? Distance between Na + and Cl - is 282 pm. Solution J 10 x 18 . 8 m 10 x 82 . 2 ) C 10 x 6 . 1 ( x ) C / m . J (8.99x10 - E 19 10 2 19 2 9 - - - - = = To express this energy for one mole of ions; mol / kJ 493 ) 10 x 02 . 6 ( x ) 10 x 18 . 8 ( E 23 19 - = - = -
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11/01/11 18:05 Dr. A. Gökmen, METU 8 Bonding in a Crystal Bonding in an ion pair extends in three dimension to form a crystal Oppositely charged ions attract, but the same charged ions repel each other. In a crystal ions are arranged to give net attraction. Lattice energy is the energy required to seperate the ions from a crystal.
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11/01/11 18:05 Dr. A. Gökmen, METU 9 Energetics of Ionic Bonding 1 mol Na + 1 mol Cl 1 mol Na + + 1 mol Cl - 1 mol NaCl(s) 1 mol Na + Cl - ion pair -493 kJ -293 kJ -786 kJ negative of lattice energy -639 kJ (net energy released) 147 kJ
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11/01/11 18:05 Dr. A. Gökmen, METU 10 Lattice Energy from Born-Haber Cycle Determination of lattice energy of NaCl is difficult. It can be calculated from a thermochemic al cycle, Born- Haber cycle Na(g) Na + (g) Cl(g) Cl - (g) + Na(s)
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