Honors Biology (4B) Oct. 14, 2015
Objective: After direct instruction and project oriented guided inquiry packet
students will describe the arrangement of charges across a water molecule
and explain the role hydrogen bonding plays in the interactions between
water molecules with 75% accuracy.
Standards: 5.1.12.D.1, 5.1.12.D.2, 5.1.12.D.3, 5.2.12.B.1, 5.2.12.B.2
Do Now (Independent Practice): Read the following article.
Identify two properties of water and explain their importance to
living organisms.
Agenda:
Notes (Direct Instruction)
Why does ice float in water? (Video Inquiry/Discussion)
Properties of Water POGIL (Guided Inquiry)
Homework (Independent Practice): Continue completing Ch. 2
Packet. In addition, complete Properties of Water POGIL if not
completed in class.
2.5 Water Molecules
Water molecules are polar
• Form hydrogen bonds with other polar molecules
• Hydrophilic substances (water-loving)
• Dissolves easily in water (w/ other polar
molecules - ex. sugar)
2.5 Water Molecules
Water molecules are polar
• Form hydrogen bonds with other polar molecules
• Hydrophobic substances (water-dreading)
• Resists dissolving in water (w/ non polar
molecules - ex. oil)
Water’s Life-Giving Properties
Polarity gives liquid water unique properties that
make life possible:
• Resistance to temperature (measure of molecular
motion) changes
• Internal cohesion
• Dissolves polar and ionic substances
• Functions as a heat reservoir
Cohesion: tendency of molecules to stick
together when a substance is under tension; a
property of liquid water
Water’s Life-Giving Properties
Water’s Cohesion
Water’s Life-Giving Properties
When the temperature of water is below its boiling
point, hydrogen bonds form as fast as they break
• Molecular motion can keep bonds from forming
• Individual molecules at the water’s surface escape
into the air
Evaporation: transition of a liquid into a gas;
requires energy input
Why does ice float in water?
http://ed.ted.com/lessons/why-does-ice-float-inwater-george-zaidan-and-charles-morton
Liquid Water: Hydrogen Bonds
Hydrogen bonding pattern among water molecules
in liquid water. Dashed lines signify hydrogen
bonds, which break and re-form rapidly.
Water Temperature:
From Ice to Evaporation
 Hydrogen bonding in ice. Below 0oC, every water molecule hydrogen-bonds
with four others, in a rigid three-dimensional lattice. The molecules are
farther apart, or less densely packed, than they are in liquid water. As a
result, ice floats.
Water’s Solvent Properties
Solvents dissolve solutes (spheres of hydration)
Solvent: substance, typically a liquid, that
dissolves other substances; e.g., water
Solute: a dissolved substance
Water’s Solvent Properties
Solvents dissolve solutes (spheres of hydration)
Sphere of hydration: a clustering of water
molecules around a solute.
Key Concepts:
NO WATER, NO LIFE
Life originated in water and is adapted to its
properties
Water has temperature-stabilizing effects, cohesion,
and a capacity to act as a solvent for many other
substances
These properties make life possible on Earth
Crash Course Water (Liquid Awesome)
https://www.youtube.com/watch?v=HVT3Y3_gHGg
Closure
a. Describe the arrangement of charges across a water
molecule.
b. What role does hydrogen bonding play in the
interactions between water molecules? Include a sketch.