Honors Biology (4B) Oct. 12, 2015
Objective: Students will model ionic and covalent bonds by drawing lewis dot
structures and showing electron transfer as well as electron sharing with
80% accuracy. 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):
a. Describe the arrangement of electrons in atoms.
 In your description include: orbital organization, a shell
model example, characteristics of reactivity, and ionization.
b. Describe the different types of chemical bonds.
 In your description include: examples, and characteristics
(i.e. electronegativity, electron activity, polarization, etc.).
Agenda:
Chemical Bonding Modeling (Guided Inquiry)
Homework (Independent Practice): Continue completing Ch. 2
Hydrogen Bonds
Hydrogen Bond: Attraction that forms between a
covalently bonded hydrogen atom and an
electronegative atom taking part in another covalent
bond.
Form between a hydrogen atom and an electronegative
atom
• Each with separate polar covalent bonds
Are not chemical bonds
• Do not make atoms into molecules
• Individually weak
• Collectively stabilize structures of large molecules
Hydrogen Bonds
Key Concepts:
ATOMS BOND
Key Concepts:
ATOMS BOND
Atoms of many elements interact by acquiring, sharing, and
giving up electrons.
A chemical bond may be ionic or covalent depending on the
atoms taking part in it.
An ionic bond is a strong mutual attraction between two ions
of opposite charge. Ionic bonds are very polar.
Atoms share a pair of electrons in a covalent bond. When the
atoms share electrons unequally, the bond is polar.
Ionic, covalent, and hydrogen bonds are the main interactions
between atoms in biological molecules
Water you talking about?
Discuss the following properties of water with your table
(group)
Think:
What is the importance of each property to life on
earth?
What would happen if water did not have its unusual
structure, and consequently did not exhibit this characteristic?
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
Closure
Chose one of the characteristics of water discussed
today.
a. Explain the importance of the property you selected to
life on earth.
b. Explain what would happen if water did not have its
unusual structure, and consequently did not exhibit this
characteristics.