Section 21.1 - CPO Science
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Transcript Section 21.1 - CPO Science
UNIT SEVEN: Earth’s Water
Chapter 21 Water and Solutions
Chapter 22 Water Systems
Chapter 23 How Water Shapes the
Land
Chapter Twenty-One: Water and
Solutions
21.1 Water
21.2 Solutions
21.3 Acids, Bases, and pH
Chapter 21.1 Learning Goals
Describe water in terms of its polarity.
Discuss properties of water related to
hydrogen bonding.
Explain why water is a good solvent.
Investigation 21A
Solubility
Key Question:
What does it mean to dissolve?
21.1 Water
We live on a watery planet.
All life on Earth depends on this
combination of hydrogen and
oxygen atoms.
What are the properties of water
that make it so valuable?
21.1 The shape of a water molecule
When two hydrogen
atoms each share one
electron with an
oxygen atom, a
neutral molecule is
formed.
21.1 The shape of a water molecule
Because negative
charges repel, the
electrons pairs around
the oxygen atom are
located where they are
the farthest apart.
This results in a
geometric shape called a
tetrahedron.
21.1 Water is a polar molecule
A water molecule has
a negative end (pole)
and a positive end.
A molecule (like water)
with a charge
separation is called a
polar molecule.
21.1 Another polar molecule
Ammonia, NH3, is
another polar molecule.
With one lone pair and
three bonding pairs of
electrons.
This gives the ammonia
molecule a pyramid
shape.
21.1 Methane is nonpolar
Methane, CH4, is a
nonpolar molecule.
Since there are no
lone pairs of
electrons, the
electrons are shared
equally between
atoms.
21.1 Hydrogen bonds
A hydrogen bond is a bond between the
hydrogen on one molecule to another
atom on another molecule.
Hydrogen bonds are relatively weak so
they constantly break and re-form.
21.1 Ice and hydrogen bonds
Frozen water (or ice)
has an organized
structure that
resembles a
honeycomb because
each water molecule
can form hydrogen
bonds with four other
water molecules.
21.1 Properties of water
Water has a high
specific heat value
because of hydrogen
bonds.
In order for water to
boil, enough energy
must be added to
separate the hydrogen
bonds.
21.1 Plants and hydrogen bonds
The attraction
between water
molecules helps
water travel from
roots to stems and
leaves.
21.1 Water is a universal solvent
Water dissolves
sodium chloride
(salt) to form a
solution of sodium
(+) and chlorine (-)
ions.
21.1 Water is a universal solvent
In general, like
dissolves like:
water dissolves
polar substances
non-polar solvents
dissolve non-polar
substances