chem161sg_chapter9

chem161sg_chapter9 - Chapter 9 Chemical Bonds Chemical...

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Chapter 9 Chemical Bonds Chemical bonds are… strong attractive forces that exist between atoms in a molecule. Types of Chemical Bonds Metallic The valence electrons form a band of electronic cloud surrounding the nucleus. Na + Na + Na + Na + Na + Na + Ionic Results from the attraction between positive (cation) and negative (anion) ions. Ionic compounds like Na + Cl …are solids at normal temperatures and pressures. …formed between elements that vary greatly in electronegativities. Covalent Results from sharing an electron pair between two atoms. Covalent compounds are molecular solids, liquids, or gases… H 2 O (s), H 2 O (l), H 2 O (g) O 2 (g) …generally formed between elements of comparable electronegativities. Chemical bond-preview + E r 0 Potential Energy Diagram As the two hydrogen atoms come close to each other, the electron clouds overlap to give a bond , which is composed of two electrons shared between the two atoms. – 436 kJ/mol for H – H H H 1
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Theory for Chemical Bonding-An Overview 1. Valence electrons play a fundamental role in bonding. 2. Transfer of electron(s) from one atom to another generates a cation and an anion that attract each other, resulting in ionic bonding. 3. Sharing an electron pair between atoms result in covalent bonding. 4. In gaining ,losing or sharing electrons, atoms acquire noble gas configuration. Lewis Symbols These are e -dot symbols where the valence electrons are represented by dots . L i N a B e N F Lewis symbols do not specifically reflect electron pairing as is done above for Be. : : .. . . . . . . : Ionic Bonding …is a chemical bond formed by the electrostatic attraction between positive and negative ions. q 1 and q 2 are the magnitude of F α the charges attracting each other r: the distance between the two charges q 1 q 2 2 Ionic bonding results when there is a complete transfer of electron(s) from one atom to another atom. Na + Cl Na + + Cl : : 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 3p 5 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 6 : : . . 2
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Lewis formula for ionic compounds: Keep track of the electrons… Na + F Æ Na + F Ba + O Æ Ba 2+ O 2– Note: Na Æ Na + + e 2 s 2 2p 6 3s 1 2s 2 2p 6 } complete octet, like that of [Ne] e + F Æ F 2 s 2 2p 5 2s 2 2p 6 } complete octet, like that of [Ne] However: Li Æ Li + + e 1 s 2 2s 1 1s 2 } inert gas configuration like that of [He] "duet" H + e Æ [H ] 1 s 1 1s 2 Ga Æ Ga 3+ + 3 e [Ar] 3d 10 4s 2 4p 1 [Ar] 3d 10 Additional filled subshell, 3d 10 ; these electrons are tightly held and difficult to lose. Note: with metals, hydrogen accepts an electron and become H - , a hydride. : : .. : : : . . . : : : : . : : . : . . . : 3
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The Energetics of formation of NaCl (s) from its constituent elements: Na (g) + Cl (g) Æ NaCl (s) 1. Ionization Energy of Na (g) Na (g) + IE Æ Na + (g) + e 2. Electron Affinity of Cl (g) Cl (g) + e Æ Cl (g) + EA Reactions: Energy Change: Na (g) + IE Æ Na + (g) + e + 496 kJ/mol Cl (g) + e Æ Cl (g) + EA – 349 kJ/mol + 147 kJ/mol Na (g) + Cl (g) + 147 kJ Na + (g) + Cl (g) i.e. isolated formation of these ions is not favorable one needs 147 kJ/mol to do it.
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This note was uploaded on 09/30/2011 for the course CHEM 161 taught by Professor Vacillian during the Spring '08 term at Rutgers.

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chem161sg_chapter9 - Chapter 9 Chemical Bonds Chemical...

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