chemistry - bond polarity

non-polar

• in covalently bonded molecules where the atoms are the same (cl2,br2 ) the electrons are equally distributed between the 2 bonding atoms

• a bond is non-polar if the electrons lie equally between the 2 atoms

polar

• in covalent bonds between different atoms, one atom has a stronger attraction for the electrons than the other atom. The electrons lie to one end of the molecule

• a bond is polar if the electrons lie closer to one of the atoms than another. A permanent dipole is formed

• contains a permanent dipole which is a small charge difference across a bond resulting from a difference in the electronegativity of the bonding atoms

electronegativity

• electronegativity is the ability of an atom to attract a bonding pair of electrons in a covalent bond

• there are tables of electronegativity values that can be used to predict how polar a covalent bond is

• the greater the difference in electronegativity, the greater the permanent dipole and the more polar the covalent bond

non-polar molecules

• symmetrical molecules are non-polar even if they have polar bonds because the dipoles can cancel each other out

polar molecules

• unsymmetrical molecules which contain one or more polar covalent bonds are polar because the dipoles cannot cancel each other out