chap08and05_07bch1049_MCWC1a

chap08and05_07bch1049_MCWC1a - Concepts of Chemical Bonding...

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1 Chemical Bonding Concepts of Chemical Bonding (Chapter 8) What’s Ahead: 1. 1. Types of Chemical Bonds and Lewis Symbols Types of Chemical Bonds and Lewis Symbols 2. 2. Ionic Bonding and Lattice Energy Ionic Bonding and Lattice Energy 3. Covalent Bonding, Bond Polarity and Electronegativity Covalent Bonding, Bond Polarity and Electronegativity 4. 4. Chapter 5 Chapter 5 5. 5. Bond Enthalpies: Strengths of Covalent Bonds Bond Enthalpies: Strengths of Covalent Bonds Chemical Bonding Chemical Bonds • Three basic types of bonds: ¾ Ionic • Electrostatic attraction between ions ¾ Covalent • Sharing of electrons ¾ Metallic • Metal atoms bonded to several other atoms
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2 Chemical Bonding The valence electrons are shown. Each dot represents one valence electron. Octet Rule: Atoms tend to gain, lose or share electrons until they have a fully occupied outer shell (like noble gas). Chemical Bonding
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3 Chemical Bonding Energetics of Ionic Bonding We get 349 kJ/mol back by giving electrons to chlorine (electron affinity). 496 349 = 147 kJ/mol So why is the reaction exothermic? As we saw previously, it takes 495 kJ/mol to remove electrons from sodium (ionization energy). Chemical Bonding Ionic Bonding • Electrostatic attraction between the newly formed sodium cation and chloride anion, resulting in… lattice energy.
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4 Chemical Bonding • Lattice energy (measure of the amount of stabilization): The energy required to completely separate a mole of a solid ionic compound into its gaseous ions. The reverse process is therefore highly exothermic. • Energy of interacting particles is governed by Coulomb’s law ( Q 1 and Q 2 charges of particles, d distance, κ constant): E el = Q 1 Q 2 d Energetics of Ionic Bonding NaCl(s) ⎯⎯→ Na + (g) + Cl ( g ) Δ H lattice = +788 kJ/mol Chemical Bonding Lattice Energy • Hence, lattice energy increases with the charge on the ions. • It also increases with decreasing size of ions. E el = Q 1 Q 2 d
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5 Chemical Bonding Covalent Bonding Electrons are shared between atoms. Covalent bond in H 2 contain several electrostatic interactions: ¾ Attractions between electrons and nuclei ¾ Repulsions between electrons ¾ Repulsions between nuclei • Electron distribution shown for H 2 . Attraction results in concentration of electron density between nuclei: ¾ Overall interaction is attractive . ¾ 2 nuclei attracted to –ve charge in between. ¾ Shared electron pair acts as ‘glue’ to bind atoms together . H Cl δ+ δ Cl 2 HCl Polar Covalent Bonds • Although atoms form compounds by sharing electrons, the electrons are not often shared equally. • Cl tends to attract electrons, or pulls harder on the shared electrons than H, to give a polar bond . • Therefore, the Cl end of the molecule has more electron density (partial –ve charge, in red) than the H end (partial +ve charge, in blue).
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6 Electronegativity Chemical Bonding Electronegativity (EN): • The ability of atoms in a molecule to attract electrons to itself.
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chap08and05_07bch1049_MCWC1a - Concepts of Chemical Bonding...

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