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Polarity

15 Sept 20242 min read

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  • Electronegativity is the ability of an atom in gaseous phase to attract electrons to itself

Bond Polarity

  • The property of shared pairs of electrons being closer to one atom than the other in a covalent bond results in an uneven distribution of electrical charge along the bond. This uneven distribution of charge is called bond polarity

Polar Covalent Bonds

  • Occur when 2 atoms of different EN share electrons
  • The difference in EN leads to an uneven sharing of electrons, thus an uneven distribution of charge, as the electrons spend more time towards the highly EN atom and so the more EN atom becomes partially negative and the less EN atom becomes partially positive
  • The uneven distribution of charge caused by the difference in EN of the atoms involved in the covalent bond is known as a bond dipole as one side of the bond is partially positive, and the other side is partially negative

Pure Covalent Bonds

  • Pure covalent bonds form when atoms of equal EN form covalent bonds leading to an equal sharing of electrons and an even distribution of charge between the 2 atoms; leading to no net dipole

Ionic Bonding

  • Ionic bonding occurs when atoms of vastly different EN form covalent bonds leading to a complete transfer of electrons from a lower En atom (usually metal atom) to the highly EN atoms (non metal) resulting in the formation of ions that form ionic bonds due to electrostatic attraction between them

Net Dipole/Molecular Polarity

  • A net dipole is the vector sum of all the bond dipoles occurring within a molecule (greater than 0), due to the molecule being unsymmetrical and there being a net uneven distribution of charge in the molecule
  • This means that one pole/side of the molecule will have a partially positive charge while the other will have a partially negative charge. When there is a net uneven distribution of charge within a molecule and the 2 opposites’ sides’ “poles” have differing charges; a net dipole exists and the molecule is said to be polar

How to Determine Polarity

  1. Draw an electron dot (Lewis) diagram and figure out the shape
  2. Draw individual bond polarities and figure out the vector sum
  3. If the molecule is asymmetrical, then the vector sum should point in a net direction; that molecule is then polar

Charge does not mean it is polar, polar does not mean it is charged

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