Formal charge = Valence electrons - Non-bonding electrons - $\frac{1}{2}$(Bonding electrons)

Used to identify most stable resonance structures:

• Minimize formal charges
• Negative charge on more electronegative atom
• Like charges should not be on adjacent atoms

Dipole moment (mu = q x d):

• Vector quantity — direction matters for net molecular dipole
• Symmetrical molecules: Net dipole = 0 (CO2, BF3, CH4, CCl4)
• cis-isomers generally have higher dipole moments than trans-isomers
• 1,4-dichlorobenzene: mu = 0 (vectors cancel). 1,2-dichlorobenzene: highest mu among isomers.

JEE application: Dipole moment helps distinguish isomers — especially cis/trans and ortho/meta/para.