BLB8S - Chapter 7 1 Chemistry 101 Chemistry 101 Prof. Jerry...

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Unformatted text preview: Chapter 7 1 Chemistry 101 Chemistry 101 Prof. Jerry Keister Chapter 7 2 Basic Concepts of Basic Concepts of Chemical Bonding Chemical Bonding Chapter 8 Chapter 8 Chapter 7 3 Atoms are attached to one another to form polyatomic compounds by three kinds of chemical bonds: Covalent bonds involve sharing of electron pairs between atoms. Ionic bonds are electrostatic interactions between oppositely charges entities (ions) which can be thought to arise by electron transfer from one atom to another. Metallic bonds are delocalized sharing of electrons by many metal atoms. Chemical Compounds Chemical Compounds Chapter 7 4 Ionic Bonds and Ionic Solids Ionic Bonds and Ionic Solids 01 01 Ionic bonds form when an element that easily gives up an electron ( small E i values ) comes in contact with an element that accepts an electron ( negative E ea values) . 1 s 2 2 s 2 2 p 6 3 s 1 1 s 2 2 s 2 2 p 6 3 s 2 3 p 5 1 s 2 2 s 2 2 p 6 1 s 2 2 s 2 2 p 6 3 s 2 3 p 6 Na + Cl Na + Cl Chapter 7 5 Ionic Bonding Ionic Bonding Energetics of Ionic Bond Formation Energetics of Ionic Bond Formation The formation of Na + ( g ) and Cl- ( g ) from Na( g ) and Cl( g ) is endothermic. Why is the formation of NaCl( s ) exothermic? The reaction NaCl( s ) Na + ( g ) + Cl- ( g ) is endothermic ( H = + 788 kJ/mol). Chapter 7 6 Ionic Bonding Ionic Bonding NaCl forms a very regular structure in which each Na + ion is surrounded by 6 Cl- ions. Similarly, each Cl- ion is surrounded by six Na + ions. There is a regular arrangement of Na + and Cl- in 3D. Note that the ions are packed as closely as possible. Note that it is not easy to find a molecular formula to describe the ionic lattice. Chapter 7 7 Ionic Bonding Ionic Bonding Chapter 7 8 Ionic Bonding Ionic Bonding Energetics of Ionic Bond Formation Energetics of Ionic Bond Formation The energy required to separate one mole of ions in an ionic lattice into gaseous ions is called the lattice energy , U or H lattice . Lattice energy depends on the charge on the ions, and the size of the ions. The specific relationship is given by Coulombs equation: as Z 1 and Z 2 increase, U increases; as d increases, U decreases. d Z Z k U 2 1 =- Chapter 7 9 Ionic Bonding Ionic Bonding Born-Haber Cycle Born-Haber Cycle This is a thermodynamic cycle that analyzes lattice energy precisely. The Born-Haber cycle looks at the formation of NaCl( s ) from Na( s ) and Cl 2 ( g ). The direct route is H f : Na( s ) and Cl 2 ( g ) NaCl( s ), H = -410.9 kJ Alternatively, we can form sodium gas ( endothermic ), then chlorine atoms ( endothermic ), then sodium ions (ionization energy for Na, endothermic ), then chloride ions (electron affinity for Cl, exothermic ), then form the ionic lattice ( exothermic ). Chapter 7 10 Ionic Bonding Ionic Bonding Born-Haber Cycle Born-Haber Cycle The sum of the energies is -410.9 kJ. Chapter 7 11 Ionic Bonding Ionic Bonding Energetics of Ionic Bond Formation Energetics of Ionic Bond Formation Chapter 7...
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BLB8S - Chapter 7 1 Chemistry 101 Chemistry 101 Prof. Jerry...

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