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