Electronegativity and polarity

• Electronegativity: The attraction of a bonded atom for the pair of electrons in a covalent bond
• Electronegativity increases across the periodic table as nuclear charge increases and atomic radius decreases, so along periods and up the groups.
• Electronnegativity is measured using the Pauling scale, which is used to compare the electronegativity of the atoms of different elements. A large Pauling value indicates that the atoms of that element are very electronegative.

  Nitrogen, oxygen, fluorine, chlorine and the non-metals are the most electronegative. The group 1 metals are the least electronegative.
• Electronegativity values can be used to estimate the type of bonding. If the electronegativity difference is large, one bonded atom has a much greater attraction for the shared pair than the other bonded atom. The more electronegative atom will have gained control of the electrons and the bond will now be ionic rather than covalent.
• A non-polar bond is when the bonded electron pair is shared equally between the bonded atoms. This bond happens when:

  • The bonded atoms are the same
  • The bonded atoms have the same or similar electronegativity

  In molecules of elements like hydrogen, oxygen, and chlorine, the electron pair is shared equally as they are the same element this makes the bond a pure covalent bond.
• In a polar bond, the bonded electron pair is shared unequally between the bonded atoms. This happens when the bonded atoms are different and have different electronegativity values. This results in a polar covalent bond.
• Polar covalent bond

  A bond with permanent dipoles, having slightly positive and slightly

  negative partial charges on the bonded atoms.
• Dipole

  A separation in electrical charge so that one atom of a polar covalent bond, or one end of a polar molecule, has a slightly positive and the other has a slightly negative charge.
• A dipole in a polar covalent bond does not change and is called a permanent dipole
• Depending on the shape of the molecule, the dipoles may reinforce one another to produce a larger dipole over the whole molecule or cancel out if the dipoles act in opposite directions like in carbon dioxide.
• A molecule can non-polar but contain polar bonds when the molecule is symmetrical which cancel put the partial charges.