Review, Hydrogen Bonding and Water AP Biology

Biology, Sixth Edition Chapter 2, Atoms and Molecules Ionic Bonds electrons are donated by one atom to another An electronegative atom steals an electron from another atom to fill its valence shell

Biology, Sixth Edition Chapter 2, Atoms and Molecules Ionic Bonds in Salt

Biology, Sixth Edition Chapter 2, Atoms and Molecules Covalent Bonds two electrons are shared per bond The outer shells of both atoms become filled More than one bond can occur between two atoms

Biology, Sixth Edition Chapter 2, Atoms and Molecules Thinking About Covalent Bonds The Lewis structure uses dots to indicate the number of electrons in the valence shells of atoms: In contrast, a structural model uses a line to represent the shared pair of electrons: methane

2 types of covalent bonds 1.Nonpolar – share electrons equally 2.Polar – share electrons unequally

Biology, Sixth Edition Chapter 2, Atoms and Molecules Electronegative O pulls e- from H This causes a partial (+) charge on the H, and a partial (-) charge on the O Partial charges are indicated by lower case deltas (  ) The bonds between O and H are polar covalent bonds   Polar Covalent Bonds

Biology, Sixth Edition Chapter 2, Atoms and Molecules Partial charges interact Hs attracted to Os Causes water to self-associate Water Forms Hydrogen Bonds

Biology, Sixth Edition Chapter 2, Atoms and Molecules Hydrogen Bonding Gaseous water molecules interact very little Liquid water molecules are hydrogen bonded, but can slip past each other As water freezes, it forms a crystalline lattice because H bonding lasts longer

Biology, Sixth Edition Chapter 2, Atoms and Molecules Water is “Sticky” Water is sticky because of H bonding Cohesive – sticks to itself Adhesive – sticks to other things – Meniscus

Biology, Sixth Edition Chapter 2, Atoms and Molecules Water has High Surface Tension Water sticks to itself strongly and so has high surface tension – Forms meniscus – Forms droplets – Small animals can ‘skate’ on surface

Other water properties High specific heat High heat of vaporization Great solvent