Pre-Assessment
• Balance the following equation:
H2 + O2  H2O
• Sketch a molecule of water. Show the
covalent bonding that exists in the
molecule.
• Why is the existence of water important in
the search for extraterrestrial life?
Enduring Understanding:
Water’s polarity and hydrogen
bonds give it unique, life
supporting properties
Section 4.4
I. Unequal electron (e-) sharing
creates polar molecules
• An atom’s attraction for
shared electrons is called its
_electronegativity_____
• _oxygen_____ is highly
electronegative
• Oxygen in water “tugs” on
shared e- more strongly than
hydrogen, therefore e- spend
more time near oxygen atom
• Unequal sharing produces
polar covalent bond
• A polar molecule is one that
has an unequal distribution of
charge
II. Hydrogen bonds are weak bonds
between an electronegative atom
and a hydrogen atom with a positive
region.
• Each water molecule
can hydrogen bond to
as many as _4__
partners.
• During which phase
of water (solid, liquid,
gas) do the most H
bonds exist? _solid_
The least? _gas__
III. Hydrogen bonds account for
water’s cohesive property
• Cohesion is the tendency for _molecules of
the same kind to stick to each other_____
• Adhesion is the tendency for _unlike
molecules to attract__________
• In what ways does this property of water
support life?
IV. Hydrogen bonds give water an
unusually high surface tension
• Surface tension- a
measure of how
difficult it is to stretch
or break the surface
of a liquid
What effect does soap have on
surface tension?
_________________________
Soap has a water
loving end and a
water hating end.
When it is added to
water, it separates the
water molecules and
reduces surface
tension.
V. Due to hydrogen bonding water has a
better ability to resist temperature
change than most other substances.
• Temperature measures the intensity of heat-the
average speed of molecules.
• When two substances differ in temperature, thermal
energy in the form of _heat___ will transfer from _the
warmer substance to the cooler one______.
• Heat must be _absorbed_ to break H bonds. Thus
water requires lg amount of heat to warm up few
degrees
• When water is cooled, more H bonds form, releasing
_heat___ and slowing the cooling process.
• How does this unique property support life?
VI. Ice is less dense than liquid
water due to hydrogen bonding.
How does this unique
property of water support
life?
______________________
VII. Water’s versatility as a solvent
results from the polarity of its
molecules.
•
•
•
•
•
•
Solvent- __________________________
Solute- ___________________________
Aqueous solution- __________________
Dissolving capability due to ___________
Dissolves _____ and ______ compounds
What role does this unique property have
in supporting life? ___________________
__________________________________
Why does salt dissolve in
water?
The negative
ends of water
surround the
positive sodium
ions.
The positive ends
of the water
molecule surround
the negative
chlorine atoms.
Why doesn’t oil dissolve in water?
Oil is non polar, so does not interact with water. It
forms a single layer above it, sticking its water fearing
ends out.