P

2.4.0 - Polarity

Introduction

  • ^^Polarity^^ - “The distribution of electrical charge over the atoms connected by the bond” (x)
  • The difference in electronegativity between elements in a molecule determines whether the overall molecule is polar or nonpolar.'
  • Difference in electronegativity causes partial positive (𝛿+) and negative charges (𝛿-).
  • A molecule with two of the same element will always result in a nonpolar bond (i.e, they are not polar opposites in terms of their ability to attract electrons)
  • Polarity of molecule affected by structure - existence of lone pairs will affect shape and polarity.

Shape & Polarity

  • Shape determines the distribution of the partial charges within the molecules.
  • ^^Dipole^^ - molecule where the ends have opposing charges.
  • Polar if:
    • Distinctive regions of charges
    • Non-symmetrical shapes (frequently)
  • Non-polar if:
    • No distinctive regions of charges
    • Symmetrical shapes (frequently)

Determining Polarity of a Molecule

  • Assign partial charges (electronegativity) to all atoms within the molecule, based on the “flow of electrons'“

    • e.g in barium fluoride (BF3), fluorine, the most electronegative element, will have a partial charge of (𝛿-) as the negatively charged electrons from barium will ‘drift’ towards it. Barium will have a partial charge of 𝛿+.
  • Determine whether each bond is polar or non polar. If the molecule has no polar bonds or it is symmetrical, it is nonpolar.

Electronegativity to determine Polarity

  • Electronegativity used to determine polarity of a molecule.
  • The greater the difference between electronegativity values, the more polar it is.
Approx. Electronegativity DifferenceType of BondExample
0.0 - 0.4Covalent (non polar)H-H
0.4 - 1.0Covalent (moderately polar)H-Cl
1.0 - 2.0Covalent (highly polar)H-F
>2.0ionic