6.2 Electronegativity and polarity

• A covalent bond is the electrostatic attraction between a shared pair of electrons and the nuclei of the two bonded atoms
• When the bonded atoms are the same, the pair of electrons in the covalent bond is equally shared
• When the bonded atoms are different, the sharing of electrons may be unequal
• Electronegativity is the ability of an atom to attract the bonding electrons in a covalent bond
• Pauling electronegativity values are used to compare the electronegativity of atoms of different elements
• The greater the number, the greater the electronegativity
• Fluorine is the most electronegative element
• The closer an element is to fluorine, the more electronegative it is
• In a polar bond, the shared pair of electrons is shared unequally between the bonding atoms
• The atom of the more electronegative element has a partial negative charge
• The atom of the less electronegative element has a partial positive charge
• Polar bond = covalent bond between atoms with different electronegativities with positive and negative partial charges on the bonded atoms
• A dipole is the separation of partial charges in a molecule
• A permanent dipole is the separation of partial charges across a polar bond arising from different electronegativities
• For molecules with more than one polar bond, the dipoles in the polar bonds may cancel out due to their position
• If the molecule is symmetrical, the dipoles in the polar bonds cancel each other out and the molecule is non-polar
• If the molecule is not symmetrical, the dipoles in the polar bonds don't cancel out and the molecule is polar