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Electronegativity and Polarity

Electronegativity and Polarity. Section 9-5. Electron affinity. Tendency of atom to accept electron Usually increases as atomic numbers increase within period Usually decreases as atomic number increases within a group. Linus Pauling. Developed scale of electronegativity

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Electronegativity and Polarity

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  1. Electronegativity and Polarity Section 9-5

  2. Electron affinity • Tendency of atom to accept electron • Usually increases as atomic numbers increase within period • Usually decreases as atomic number increases within a group

  3. Linus Pauling • Developed scale of electronegativity • Figure 9-15, pg 263 • Fluorine has the highest: 3.98 • Francium has the lowest: 0.7 • Noble gases are not given (0)

  4. Electron Affinity tells us… • Character and type of bond • Never completely ionic or covalent • Sharing is not always completely equal

  5. Ionic Bond • Large differences in electronegativity indicate that electrons are transferred

  6. Nonpolar covalent bonds • Difference in electron affinity of atoms involved is very small • Electrons shared fairly equally

  7. Identical Atoms • Difference in electronegativity is 0 • Electrons are shared equally.

  8. Polar Covalent Bonds • Unequal sharing • Electron tug-of-war • Stronger affinity = greater strength

  9. Differences • Less than 0.4 = nonpolar covalent bond • 0.4 – 1.7 = polar covalent bond • Greater than 1.7 = ionic bond

  10. Examples: • H and Br 2.20 and 2.96 = 0.76 polar covalent • C and O 2.55 and 3.44 = 0.89 polar covalent • Li and F 0.98 and 3.98 = 3.00 ionic bond

  11. Solubility of Polar Molecules • Like dissolves like • Polar (and ionic) compounds are soluble in polar substances • Nonpolar only soluble in non-polar substances

  12. Properties of Covalent Compounds • Van der Waals forces: weak forces of attraction between individual molecules

  13. Types of Intermolecular Forces • Nonpolar • Weak attraction • Dispersion or induced dipole • Polar • Stronger attraction • Dipole-dipole force • Hydrogen bond • Very strong • Between H and another dipole

  14. Physical properties • Melting/boiling points lower than ionic • Many are gases at room temp • Non-conductors of heat or electricity • Extremely hard *Due to the intermolecular forces!!

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