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.