The Properties and Importance of Water
Organisms are
Composed of
Elements... Usually
Combined into
Compounds
Slide 1
Trace Elements
are Common
Additives to
Food and Water
Slide 3
• Living organisms are composed of _______.
• Matter is composed of chemical elements.
– About 25 elements are essential for human life.
– Four elements make up about 96% of the weight of most
living organisms.
• Compound -
Some trace elements are required to prevent disease.
Fluoride Chemicals are added to food to
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Radioactive
Isotopes Can
Help or Harm Us
Slide 4
• Radioactive isotopes are useful as tracers for monitoring the
fate of atoms in living organisms.
Chemical Bonds:
The Distribution of
Electrons Determines
an Atom’s Chemical
Properties
Slide 5
• Electrons can be located in different electron shells, each with a
characteristic distance from the nucleus.
• Sophisticated imaging instruments can detect them.
• An atom whose outer electron shell is not full tends to interact
with other atoms and share, gain, or lose electrons, resulting in
attractions called chemical bonds.
•
1
Covalent Bonds Join
Atoms into Molecules
Through Electron
Sharing
Slide 6
• In a nonpolar covalent bond, electrons are shared equally.
• In polar covalent bonds, such as those found in water, electrons are
pulled closer to the more electronegative atom.
•
•
Ionic Bonds are
Attractions Between
Ions of Opposite
Charge
Slide 8
• An ion is an atom or molecule with an electrical charge resulting
from gain or loss of one or more electrons.
• Two ions with opposite charges attract each other.
– When the attraction holds the ions together, it is called an
ionic bond.
– Salt is a synonym for an ionic compound.
Hydrogen Bonds are
Weak Bonds Important
in the Chemistry of
Life
Slide 9
• One of the most important types of weak bonds is the hydrogen
bond.
• The hydrogen atoms of a water molecule are attached to oxygen
by polar covalent bonds.
• Because of these polar bonds and the wide V shape of the
molecule, water is a polar molecule.
Chemical Reactions
Make and Break
Chemical Bonds
Slide 10
Chemical Reaction -
2
Hydrogen Bonds
Make Liquid
Water Cohesive
Slide 13
Water’s
Hydrogen Bonds
Moderate
Temperature
Slide 14
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Cohesion -
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Adhesion -
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Surface Tension -
• Heat is absorbed when hydrogen bonds break and released when
hydrogen bonds form.
– This helps keep temperatures relatively steady.
– As the most energetic water molecules evaporate, the
surface of a substance cools.
Evaporative Cooling-
Ice Floats
Because it is
Less Dense than
Liquid Water
Slide 16
• Water exists as a ________, ________,or _________
• Water is less dense as a solid than a liquid because of hydrogen
bonding.
• When water freezes, each molecule forms a stable hydrogen bond
with its neighbors.
– As ice crystals form, the molecules are less densely packed
than in liquid water.
• Water floats because______________________________
•
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Water is the
Solvent of
Life
Slide 18
• Solution -
• Water’s versatility as a solvent results from the polarity of its
molecules.
• Polar or charged solutes dissolve when water molecules surround
them, forming aqueous solutions.
The Chemistry
of Life is
Sensitive to
Acidic and
Basic
Conditions
Slide 20
The Search for
Extraterrestrial
Life Centers on
the Search for
Water
Slide 23
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In liquid water, a small percentage of water molecules break apart
into ions.
We use the p H scale to describe how acidic or basic a solution is.
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Buffer -
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• The emergent properties of water support life on
Earth and may contribute to the potential for life
to have evolved on other planets.
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