Chapter8 - 1 TYPES OF CHEMICAL BONDING Ionic Bonding - two...

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1 TYPES OF CHEMICAL BONDING Ionic Bonding - two atoms of opposite charge electrically attracted to one another Covalent Bonding - two atoms each sharing electrons within a molecular orbital Metallic Bonding - positive metal ions held together in a lattice with a “sea of electrons” An actual chemical bond is a blend of all three types of bonding. Most often, one type is dominant over others. We will concentrate on ionic and covalent bonding. LEWIS STRUCTURES Only valence electrons are important in bonding. Lewis dot structures show valence electrons surrounding atom. We visualize the four valence orbitals of an atom as the sides of a box. Electrons are put into orbitals according to Hund’s rule. Examples Be has 2 valence electrons. Therefore Lewis structure is N has 5 valence electrons. Br has 7 valence electrons. C has 4 valence electrons. OCTET RULE – Generally atoms prefer electron configurations with 8 valence electrons. Atoms bond with each other so that every atom has 8 electrons in its outer shell. - Atoms may take electrons from each other or they may share electrons. Octet rule is able to explain a lot of chemistry. I. e., it is able to explain why certain elements combine together in specific proportions. Exceptions to the octet rule are plentiful. We will consider these later. Be N Br C
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2 IONIC BONDING - Oppositely charged ions attract each other. - Metal atoms lose e - and nonmetal atoms gain e - . - Ions attract each other to form ionic lattice. Lewis structures can be used to illustrate ionic bonding. Consider Potassium and Bromine Consider Calcium and Fluorine Lewis structures will be much more illuminating when we consider the sharing of electrons (covalent bonding). LATTICE ENERGY Lattice Energy – energy of released when positive and negative ions form crystal lattice due to their attraction for each other. Creation of ionic compound can be decomposed into many small steps. I. e., lattice energy can be decomposed into many smaller energy steps. These steps are virtual steps. We don’t do them one by one in the lab. But overall, when an ionic compound is formed, these steps must have happened somehow. A. Creation of gaseous metal ions from solid metal . 1. Heat metal to melting point. 2. Melt metal. 3. Heat molten metal to boiling point. 4. Boil metal to form metal gas atoms. 5. Ionize metal gas atoms to form metal gas ions. Br K + K + - Ca + F F F F Ca 2+
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3 B. Creation of gaseous nonmetal ions from nonmetal . 1. If solid, heat solid to melting point. 2. Melt solid. 3. If liquid, heat liquid to boiling point. 4. Boil liquid. 5. If molecular element, diassociate molecules into atoms. I 2 (g) 2 I(g) P 4 4 P(g) 6. Allow nonmetal atoms capture electrons to become nonmetal anions. C. Gaseous metal cations and gaseous nonmetal anions are attracted to each other to form solid lattice .
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This note was uploaded on 09/27/2010 for the course CHEM 220 taught by Professor Bates during the Spring '10 term at Skyline College.

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Chapter8 - 1 TYPES OF CHEMICAL BONDING Ionic Bonding - two...

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