Review, Hydrogen Bonding and Water AP Biology. Biology, Sixth Edition Chapter 2, Atoms and Molecules...
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Transcript of Review, Hydrogen Bonding and Water AP Biology. Biology, Sixth Edition Chapter 2, Atoms and Molecules...
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 BondsThe 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 equally2. 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