# 2.2.6 Molecular Polarity Recap: A dipole moment ( $$\mu$$) happens when a molecule is polar ( partial negative charge on one end and partial positive charge on the other ). * The value of the dipole moment is in the unit debye, D. * Polarity is an important trait in molecules as it gives rise to multiple characteristics: * Volatility * Solubility * Boiling point * **Molecular polarity** depends on both bond Polarity and molecular geometry.

* Molecules are polar when their bond dipoles do not cancel each other out. * May occur due to the geometry of molecule or the bonds have different magnitudes for the dipole moment. * AS seen from water and trichloromethane, the polar bonds do not cancel each other--> resulting in a net dipole charge. * Molecuels are not-polar when their bond dipoles cancel each other out * Boron triflouride * Carbon dioxide * Molcules are non-polr when all their bonds are non-polar * **Hydrocarbons ( hydrogen + carbons ),** like Ethane contain two types of bonds --> carbon-carbon bonds, and carbon-hydrogen bonds * Carbon-carbon cancels each other out, and carbon-hydrogen bonds are virtually non-polar because of the such small electronegativity difference. * The tetrahedral geometry around each carbon atom results iin a net dipole of zero, or very close to zero. * $$\therefore$$ Hydrocarbons are usually **non-polar** * Small Molecules were discussed so far--> What about long ones?

* Due to its length, they can have a region of polar and non-polar. * It leads to applications in emulsifiers, soaps, and detergents, as well as the phospholipid bilayer in cell membranes. **Teacher notes:** if seen lone pairs in central atom it is a polar compound since the lone pairs will bend the molecular geometry. OR \*\*If two different atoms bond to the central atom then its ....... **POLAR**