CH101 Lec5

CH101 Lec5 - CHAPTER 5: The Covalent Bond When nonmetals...

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Section 5.1 CHAPTER 5: The Covalent Bond When  nonmetals  bond to each other, a covalent  bond is formed.  The difference in electronegativity is small and the  electrons are  shared , not  transferred . Unlike ionic bonds, covalent bonds are directional  because the electrons are shared between two atoms.
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Bonding Shades of Gray Complete Sharing Elements with identical EA H—H Cl—Cl Diamond Complete transfer Na+ Cl- Alkali/Halogen Elements with very different EA Partial transfer Elements with similar EA AgCl SiO 2 CdS
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Bonds Comparison of Ionic vs Covalent  Ionic nonmetals w/ metals 2200    electronegativity electrons are transferred bonds are not directional “molecular” substances are  not formed each ion surrounded by  other ions in “extended  network”  Covalent nonmetals w/ nonmetals 2200    electronegativity electrons are shared bonds are directional “molecular” substances  formed each atom bound to  specific atoms
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Section 5.1 The Covalent Bond As two atoms approach each other, consider two  competing effects: Nuclear repulsion Electron-nuclear attraction + +  energy, nuclei repulse  each other + e + e electrons are attracted  to the other nucleus
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+ + Atoms are too far apart No interaction + + Nuclei repulse Electrons are attracted to nuclei + + Weakly bound + + Minimum Energy e /nucl vs. nucl/nucl balanced covalent bond! Section 5.1 The Covalent Bond
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+ + + + + + + + Section 5.1 The Covalent Bond (Figure 5.1) Energy Internuclear distance (distance between nuclei) atoms approach min E bond length E = Bond Energy
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+ + Spherical molecular σ bond 2 electrons are allowed It is now as if each proton gets to have 2 electrons nearby. There are 2 electrons of opposite spin in the new MO.
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Section 5.1 The Covalent Bond Bond length or bond distance (r) typically 1.0 - 2.7 Å Å = angstrom = 10  meters Bond energy typically 100 - 1000 kJ/mol Shorter bonds are stronger, have larger bond energy (potential  energy) A strong bond decreases energy of the system. Smaller atoms can get closer together!
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Section 5.2 Bond Polarity Remember electronegativity ( χ ) - the ability of an  atom to attract electrons. In H 2 , each H has the same electronegativity (“pull”) so  the electrons are located half-way between the nuclei. H H e e Nonpolar or purely covalent bond ∆ χ  = 0
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Section 5.2 Bond Polarity In HCl, Cl has a higher electronegativity (“pull”) so  the electrons are located closer to the Cl nucleus.
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CH101 Lec5 - CHAPTER 5: The Covalent Bond When nonmetals...

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