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Covalent Bonds Electronegativity differences and ionic/polar/nonpolar classification

Covalent Bonds Electronegativity differences and ionic/polar/nonpolar classification. The Ionic-Covalent Continuum. Cl. Cl. NaCl. This is the formation of an ionic bond . -. +. Na. Cl. electron transfer. and the formation of ions. Cl 2. This is the formation of a covalent bond .

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Covalent Bonds Electronegativity differences and ionic/polar/nonpolar classification

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  1. Covalent Bonds Electronegativitydifferences andionic/polar/nonpolarclassification The Ionic-Covalent Continuum

  2. Cl Cl NaCl This is the formation of an ionic bond. - + Na Cl electron transfer and the formation of ions Cl2 This is the formation of a covalent bond. sharing of a pair of electrons and the formation of molecules

  3. Comparison of Bonding Types ionic covalent ions molecules molten salts conductive non- conductive valence electrons transfer of electrons sharing of electrons high mp low mp DEN > 1.5 DEN < 1.5

  4. Electronegativity (EN) - A measure of the ability of an atom in a compound to attract electrons

  5. Electronegativity Difference: Ionic or Covalent The electronegativity difference: DEN = ENhigher – EN lower large difference small difference

  6. Using electronegativities to determine bond type DEN > 1.5 ionic bond - transfer DEN < 1.5 covalent bond - sharing So we have a range of electronegativity difference of 0 to 1.5 for sharing an electron pair.

  7. X Y DEN = 0 X Y DEN = 0.3 X Y DEN = 0.6 increasing polarity of bond X Y DEN = 0.9 polar bond 0.5 < EN< 1.5 X Y DEN = 1.2 Is the sharing of electrons in molecules always equal? non-polar bond Which element is more electronegative? ENY > ENX Direction of electron migration

  8. Space-filled BF3 – a planar molecule 4.0 F B 2.0 Ball & stick negative top side positive Electrostatic potential maps Spartan ‘02

  9. A B A+ B- A B Increasing DEN Increasing polarity 100% covalent 100% ionic Bonding spectrum Transfer

  10. Nonpolar Covalent, Polar Covalent, or Ionic Bond (Definitions) • A nonpolar covalent bond has a relatively even distribution of charge due to equal sharing of the bonding electrons. • A polar covalent bond has a relatively uneven distribution of charge due to unequal sharing of the bonding electrons. • An ionic bond results from the transfer of electrons from one bonding atom to another.

  11. Nonpolar Covalent, Polar Covalent, or Ionic Bond (Quantitatively) • A nonpolar covalent (NPC) bond has a ∆EN between 0.0 and 0.5. • A polar covalent (PC) bond has a ∆EN between 0.5 and 1.5. • An ionic bond has a ∆EN > 1.5. • The arrow of polarity points towards the element with the higher electronegativity value.

  12. not clearcut!!! • Like most things in chemistry, the distinctions between extremes are easy to recognize. There are, however, many compounds that fall in the gray area between ionic and covalent. Similarly, there are many compounds that fall in the gray zone between polar covalent and nonpolar covalent. • Another way to deal with those compounds in the middle is to say that a bond is 60% ionic and 40% covalent. • This level of analysis is beyond the scope of this course and we will use the sharp cutoffs of ∆EN > 0.5 and ∆EN > 1.5 with the recognition that such distinctions are somewhat arbitrary and do not account for all of the subtleties of bonding.

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