925 - The Covalent Bond (Figure 5.1) atoms approach + + + +...

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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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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 As   bond length,   bond energy,   energy of the system (it takes energy to keep two nuclei close together) Smaller atoms can get closer together!
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Section 5.2 Bond Polarity Remember electronegativity- 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. H Cl e e Polar covalent bond ∆ χ    0 δ δ + Partial negative  charge “dipole”
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Section 5.2 Bond Polarity As  ∆χ  increases, the bond polarity increases . NaCl     vs    NaBr χ Na  = 1.0 χ Cl  =  3.0 χ Br  =  2.8 Therefore, the NaCl bond is more polar than the NaBr bond!  Na and Br are farther apart on the periodic table so more polar!
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Section 5.2 Bond Polarity If  ∆χ  is large enough, the bond is considered  ionic , not covalent. One atom has pulled the electrons away from the other. Use   as a  guideline  but there is no distinct line  between ionic and covalent. Formerly Table 5.1:  = 0  purely covalent, no ionic character 0 <   < 0.5 mostly covalent, less than 5% ionic 0.5 <   < 1.8 polar covalent, 4 - 50% ionic  > 1.8 ionic, more than 50% ionic
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Section 5.2 Bond Polarity- Generalities If the two elements are  close  together on the periodic  table, they will form a  covalent  bond.
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925 - The Covalent Bond (Figure 5.1) atoms approach + + + +...

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