1. Bond and Molecular Polarity Courtesy of Mr. Christopherson

2. Polar Bonds l When the atoms in a bond are the same, the electrons are shared equally. l This is a nonpolar covalent bond. l When two different atoms are connected, the atoms may not be shared equally. l This is a polar covalent bond. l How do we measure how strong the atoms pull on electrons?

3. Electronegativity l A measure of how strongly the atoms attract electrons in a bond. l The bigger the electronegativity difference the more polar the bond. 0.0 - 0.5 Covalent nonpolar 0.5 - 1.0 Covalent moderately polar 1.0 -1.7 Covalent polar >1.7 Ionic

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

5. Polar Molecules Molecules with ‘ends’

6. Polar Molecules l Molecules with a positive and a negative end l Requires two things to be true ¬ The molecule must contain polar bonds This can be determined from differences in electronegativity. ­ Symmetry can not cancel out the effects of the polar bonds. Must determine geometry first.

7. Is it polar?.. H Cl Polar HH O FF B F Nonpolar H H H N Polar Nonpolar FF Cl F F F Xe FF NonpolarPolar Cl C H C H H XeF 4 CCl 4 CH 3 Cl HClH2OH2O BF 3 NH 3

8. Intermolecular Forces What holds molecules to each other?

9. Intermolecular Forces l They are what make solid and liquid molecular compounds possible. l The weakest are called van derWaal’s forces - there are two kinds l Dispersion forces l Dipole Interactions –depend on the number of electrons –more electrons stronger forces –bigger molecules

10. l Depend on the number of electrons l More electrons stronger forces l Bigger molecules more electrons fluorine (F 2 ) is a gas bromine (Br 2 ) is a liquid iodine (I 2 ) is a solid Dipole interactions

11. l Occur when polar molecules are attracted to each other. l Slightly stronger than dispersion forces. l Opposites attract but not completely hooked like in ionic solids.

12. Dipole interactions l Occur when polar molecules are attracted to each other. l Slightly stronger than dispersion forces. l Opposites attract but not completely hooked like in ionic solids. HFHF  HFHF 

13. Dipole Interactions    

14. Hydrogen bonding l Are the attractive force caused by hydrogen bonded to F, O, or N. l F, O, and N are very electronegative so it is a very strong dipole. l The hydrogen partially share with the lone pair in the molecule next to it. l The strongest of the intermolecular forces.

15. Hydrogen Bonding H H O ++ -- ++ H H O ++ -- ++

16. Hydrogen bonding H H O H H O H H O H H O H H O H H O H H O