1. Hydrogen Bonding SWBAT: Draw hydrogen bonds between two molecules

2. Definition Hydrogen Bond • A hydrogen bond is an electromagnetic attraction - not a true bond! • Hydogen must be directly bonded to a small atom with high EN (N, O, F) • Can form with another molecule (intermolecular) or another part of the same molecule (intramolecular). • The hydrogen has a partial δ+ charge and the oxygen has a partial δ- charge from being covalently bonded to an electronegative atom

3. Symbol • Covalent bond: solid line • H-bond: dotted line

4. Intermolecular H Bonding • Hydrogen bonding between two molecules – from the attraction of the dipoles

5. Intramolecular H-bonding DNA • Hydrogen bonding within its own molecule – from the attraction of the dipoles

6. Intra…..3D- Structure of Proteins

7. Intra…..3D- Structure of Proteins Hydrogen Bonding

8. Important • H-bonds do not have to involve water molecules! • All it needs is a δ+ H which can come from any molecule: • SH2, C-OH, COOH, DNA, proteins…. • And a δ- element as a neighbor (usually its O, S, N, P or the Halogen group)

9. Beryllium Chloride (tri-hydride) • BeCl2 •3H2O

10. Organic molecules and H-bonds • Draw dipole and partial charges of the following functional groups: don’t forget the unpaired Valence e- of Oxygen • COH Alcohol • CHO Aldehyde • CO Ketone • COOH Acid

11. H-Bond Drawing guide • Oppose each δ+ and δ- with one H2O • Show the δ+ and δ- and net dipole of each water molecule • Draw H-bonds as dotted lines Practice: • CH3COH •3H2O • CH3CH2 COOH •4H2O • CH2O •2H2O