2. Aim: What are polar bonds and polar molecules?

3. Polar and Nonpolar Bonds There are two types of covalent bonds Nonpolar Covalent Bonds (equal share of electrons) Polar Covalent Bonds (unequal share of electrons)

4. Polar Covalent Bond A Polar Covalent Bond is unequal sharing of electrons between two atoms (H-Cl) In a polar covalent bond, one atom typically has a negative charge, and the other atom has a positive charge

5. Nonpolar Covalent Bond A Nonpolar Covalent Bond is an equal sharing of electrons between two atoms (Cl-Cl, N-N, O-O)

7. Classification of Bonds You can determine the type of bond between two atoms by calculating the difference in electronegativity values between the elements The bigger the electronegativity difference the more polar the bond. Type of BondElectronegativity Difference Nonpolar Covalent 0  0.4 Polar Covalent 0.5  1.9 Ionic 2.0  4.0

8. Practice What type of bond is HCl? (H = 2.1, Cl = 3.1) Your Turn To Practice N(3.0) and H(2.1) N(3.0) and H(2.1) H(2.1) and H(2.1) H(2.1) and H(2.1) Ca(1.0) and Cl(3.0) Ca(1.0) and Cl(3.0) Al(1.5) and Cl(3.0) Al(1.5) and Cl(3.0) Mg(1.2) and O(3.5) Mg(1.2) and O(3.5) H(2.1) and F(4.0) H(2.1) and F(4.0) Difference = 3.1 – 2.1 = 1.0 Therefore it is polar covalent bond.

9. How to show a bond is polar Isn’t a whole charge just a partial charge  means a partially positive (less electronegative)  means a partially negative (more electronegative) The Cl pulls harder on the electrons The electrons spend more time near the Cl H Cl  

10. Polar Molecules Molecules with a positive and a negative end Requires two things to be true ¬ The molecule must contain polar bonds This can be determined from differences in electronegativity. ­ Asymmetric molecule.

12. Symmetrical Molecules Because of symmetry, molecules that have polar bonds are overall a nonpolar molecules (+ and – charges cancel out or balance out) Examples: CO 2 BF 3 CCl 4

13. Asymmetrical Molecules If a molecule has polar bonds (and there is no symmetry to cancel out + and – charges), the molecule is polar. Examples: H 2 O HCl NH 3

14. Dipole When there is unequal sharing of electrons a dipole exists Dipole is a molecule that has two poles or regions with opposite charges Dipole is a molecule that has two poles or regions with opposite charges A dipole is represented by a dipole arrow pointing towards the more negative end A dipole is represented by a dipole arrow pointing towards the more negative end

17. Practice Drawing Dipoles P- Br P = 2.1 Br = 2.8 P –Br  +  - Practice H(2.1) – S(2.5) F(4.0) - C(2.5) C(2.5) - Si(1.8) N(3.0) – O(3.5)

18. Is it Polar? HF H 2 O NH 3 CF 4 CO 2

19. Summary In a polar bond, one atom is more electronegative than the other. In a polar bond, one atom is more electronegative than the other. In a nonpolar bond, both atoms have similar electronegativities. In a nonpolar bond, both atoms have similar electronegativities. An asymmetric molecule with polar bonds is a polar molecule. An asymmetric molecule with polar bonds is a polar molecule. An asymmetric molecule with nonpolar bonds is a nonpolar molecule. An asymmetric molecule with nonpolar bonds is a nonpolar molecule. A symmetric molecule, regardless of the polarity of the bonds, is always a nonpolar molecule. A symmetric molecule, regardless of the polarity of the bonds, is always a nonpolar molecule.