Chapter 9 chem lecture

Chapter 9 chem lecture - Chapter 9 Chemical Bonding I Basic...

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Chapter 9: Chemical Bonding I: Basic Concepts Lewis Structures (electron dot structures) are a pictorial method for representing the sharing of electrons in molecules. Electron dots represent only the valance electrons, that is those involved in bonding Rule 1: n=1 can only have 2 valence electrons N=2 can only have 8 electrons N≥3 can only have 8 valence electrons BUT!! -- have nd orbitals, octet can be expanded if necessary. Na [Ne] 3s1 has 1 electron Si [Ne] 3s23p2 has 4 electrons As [Ar] 4s23d104p3 has 5 electrons Bond- forces that hold groups of atoms together and makes them function as a unit 3 general types of bonds: 1. ionic bonds 2. covalent bonds 3. metallic bonds Valence electrons participate in chemical bonding Ionic bonds: electrostatic forces that exist between ions of opposite charge. Occurs when one or more electrons from one atom are transferred to another atom Oxidation: loss of electrons Reduction: gain of electros Ionic solids: crystalline substances that results from formation of ionic bonds Often occurs between atoms with small ionization energy and atoms with large negative electron affinity
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Lattice energy (E): the energy required to completely separate one mole of a solid ionic compound into gaseous ions Sum of electrostatic interactions in a crystal-gives a measure of ionic bonds within the crystals NaCl (s) Na + (g) + Cl - (g) E=+787kj/mol Na+ (g) + Cl- (g) NaCl (s) -E= -787 kj/mol Coulomb’s Law: describes the force (F) between electrically charged particles F= K (Q1Q2) divided by r 2 K= constant Q1 and Q2= charges on the ions R= distance between the centers for the ions Lattice energy increases as Q increases and/or as r decreases Recap Group 1a elements lose ns1 valence electrons [noble gas] from previous row Group 2a elements lose ns2 valence electrons [noble gas] Group 3a elements lose ns2np1 valence electrons [noble gas] Group 7a elements gain one valence electron change from ns2np5 to ns2np6 [noble gas] within same row Group 8a elements are nearly unreactive Octet rule: main-group elements tend to undergo reactions that leave then with eight valence-shell (outer-shell) electrons
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Chapter 9 chem lecture - Chapter 9 Chemical Bonding I Basic...

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