Lec11-12 Chemical Bonding - CHEMICAL BONDING 1 Concepts in...

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LMALaput Chemistry 16 Lecture 11- 12 CHEMICAL BONDING 1. Concepts in Chemical Bonding 2. Lewis dot formulas of atoms 3. Formation of ionic compounds 4. Formation of covalent bonds 5. Bond order of covalent bonds 6. Bond lengths and bond strength 7. Writing Lewis Formulas: The Octet Rule 8. Lewis Formulas for molecules and polyatomic ions 9. Resonance 10. Formal Charges •Attractive forces that hold atoms together in compounds are called chemical bonds. •The electrons involved in bonding are usually those in the outermost shell - valence electrons . •Chemical bonding arises from the need of atoms to become stable by achieving a noble gas configuration: A fully filled orbital makes an atom stable . THE NEED FOR STABILITY 1 ST energy level needs 2 electrons 2 ND and above energy levels needs 8 electrons •Chemical bonds are classified into: - Ionic bonding results from electrostatic attractions among ions, which are formed by the transfer of one or more electrons from one atom to another. - Covalent bonding results from sharing one or more electron pairs between two atoms. - Metallic bonding results from electron pooling Types of Chemical Bonding 1. Metal with nonmetal: electron transfer and ionic bonding 2. Nonmetal with nonmetal: e lectron sharing and covalent bonding 3. Metal with metal: electron pooling and metallic bonding LEWIS DOT FORMULAS OF ATOMS •Lewis dot formulas or Lewis dot representations are a convenient bookkeeping method for tracking valence electrons . –Valence electrons are those electrons that are transferred or involved in chemical bonding. •They are chemically important. •Elements that are in the same periodic group have the same Lewis dot structures . Lewis Electron-Dot Symbols For main group elements - The A group number gives the number of valence electrons. Place one dot per valence electron on each of the four sides of the element symbol. Pair the dots (electrons) until all of the valence electrons are used. FORMATION OF IONIC COMPOUNDS •An ion is an atom or a group of atoms possessing a net electrical charge. •Ions come in two basic types: 1. positive (+) ions or cations •These atoms have lost 1 or more electrons. 2. negative (-) ions or anions •These atoms have gained 1 or more electrons. Monatomic ions consist of one atom. •Examples: –Na + , Ca2 + , Al 3+ -cations –Cl - , O 2- , N 3- -anions Polyatomic ions contain more than one atom.
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This note was uploaded on 07/09/2011 for the course SCIENCE 16 taught by Professor Uperg during the Spring '11 term at University of the Philippines Diliman.

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Lec11-12 Chemical Bonding - CHEMICAL BONDING 1 Concepts in...

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