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Polarity

Polarity. Electron Affinity. A measure of the tendency of an atom to accept an electron Increases with increasing atomic number within a period Decreases with increasing atomic number within a group. Electronegativity.

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Polarity

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  1. Polarity

  2. Electron Affinity • A measure of the tendency of an atom to accept an electron • Increases with increasing atomic number within a period • Decreases with increasing atomic number within a group

  3. Electronegativity • Electronegativity – the relative ability of an atom to attract electrons in a chemical bond • Allows us to evaluate the electron affinity of specific atoms in a compound

  4. Bond Character • A chemical bond between atoms of different elements is never completely ionic or covalent • Bond character depends on how strongly each of the bonded atoms attracts electrons

  5. Polar Covalent Bonds • Results from unequal sharing of electrons in the bond • In a covalent bond, electrons spend more time near the nucleus of the atom with the higher electronegativity

  6. Polarity • The atom that attracts electrons most strongly (has the highest electronegativity) has a slight negative charge • δ+ means partially positive • δ- means partially negative

  7. Bond Character

  8. Determining bond character • Look at HF • Electronegativity of F = 3.98 • Electronegativity of H = 2.20 • Difference: 3.98 - 2.20 = 1.78 • Electrons move towards the fluorine atom

  9. Polarity • Polarity of molecules depends on • The presence of polar bonds • The position(s) of polar bonds in the molecule (polarity is a vector quantity) • Look at H2O and BeH2

  10. Practice • Determine if the following molecules are polar • CH4 • CH2Cl2 • CHCl3 • CCl4 • CH3Cl

  11. Nonpolar Polar Polar Nonpolar Polar

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