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Unformatted text preview: CHEM 1101: CHEMISTRY (EEE/COE) LECTURE 5 INTRODUCTION TO CHEMICAL BONDS CHEMICAL BOND Definition : A chemical bond is defined as a force that acts between two or more atoms to hold them together as a stable molecule. Main types of bond : 1. Ionic or electrovalent bond, 2. Covalent bond, 3. Coordinate covalent bond Forth type of bond : Metallic bond: The type of bonding which holds the atoms together in metal crystal. Valence electron : The electrons in the outer most energy level in an atom that takes part in chemical bonding are called valence electrons. Bonding electrons : The valence electrons actually involved in bond formation are called bonding electrons. Octet rule : In chemical bond formation, atoms interact- (i) by losing, (ii) by gaining or (iii) by sharing electrons to acquire a stable noble gas configuration. He (2) 2 Ne (10) 2, 8 Ar (18) 2, 8, 8 Kr (36) 2, 8, 18, 8 Xe (54) 2, 8, 18, 18, 8 Rn (86) 2, 8, 18, 32, 18, 8 The tendency for atoms to have eight electrons in the outer shell is known as Octet rule. IONIC BOND Definition : The electrostatic attraction between the cation (+ve ions) and anions (-ve ions) produced by electron transfer constitutes an ionic or electrovalent bond. Conditions for formation of ionic bond : (1) Bond formations occur between the metal and nonmetal. Metal is donor and nonmetal is acceptor. (2) Net lowering of energy: AIUB Updated:25/09/2010 Course-Teacher: Shahrina Alam 1 A B : .. . . . B _ A + 1 valence electron 7 electron valence (cation) (anion) A + B _ A + B _ A B or A + B _ ( ) ionic bond CHEM 1101: CHEMISTRY (EEE/COE) LECTURE 5 To form a stable ionic compound, there must be a net lowering of the energy. For example- formation of NaCl molecule (a) Na e Na + 119 kcal (b) Cl + e Cl +85 kcal (c) Na + + Cl Na + Cl +187 kcal Net energy released, 187 + 85 119 = 153 kcal...
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This note was uploaded on 04/16/2011 for the course EEE 30 taught by Professor Dr.sohrabuddin during the Spring '11 term at American Intl. University.
- Spring '11