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Chapter 2
• All living beings are organized. The smallest
part of a living organism is the atom. Atoms are
the smallest part of an element. An element is
a pure substance.
• There are 25 different elements necessary to
life can be classiffied into: SPONCH (98%)
and Trace elements (elements that the body
needs in small amounts).
• The smallest particle of an element is an atom.
Different elements have different types of
atoms.
• Atoms of each element are distinguished by
a specific number of protons or Atomic
number.
• The sum of protons and neutrons produce
the Atomic mass (weight) of the element.
• Atoms of the same element with different
number of neutrons are called isotopes and
some isotopes are radioactive.
Electron arrangement determines the
chemical properties of an atom
• Electrons are arranged in shells.
• The outermost shell determines the chemical
properties of an atom.
• These shells are called “energy shells”.
4e2e-
6p+
6n
Carbon (C)
6e2e-
8p+
8n
Oxygen (O)
5e8e2e-
15p+
16n
Phosphorus (P)
2e8e8e2e-
20p+
20n
Calcium (Ca)
• Atoms whose shells are not full tend to
interact with other atoms and gain, lose, or
share electrons
Outermost electron shell (can hold 8 electrons)
Electron
HYDROGEN (H)
Atomic number = 1
First electron shell (can hold 2 electrons)
CARBON (C)
Atomic number = 6
NITROGEN (N)
Atomic number = 7
OXYGEN (O)
Atomic number = 8
Ionic bonds are attractions between ions
of opposite charge
• When atoms gain or lose electrons, charged
atoms called ions are created
• An electrical attraction between ions with
opposite charges results in an ionic bond
+
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
Na
Na+
Sodium ion
–
Cl
Cl–
Chloride ion
Sodium chloride (NaCl)
Sodium atom (neutral)
Chlorine atom (neutral)
Sodium ion (+)
Chloride ion (-)
Covalent bonds, the sharing of electrons,
join atoms into molecules
• Some atoms share outer shell electrons
with other atoms, forming covalent bonds
– Atoms joined together by covalent bonds form
molecules
• Molecules can
be represented
in many ways
The Molecule of Water
Like no other common substance, water
exists in nature in all three physical states:
– as a solid
– as a liquid
– as a gas
Why Is Water So Important to Life?
• 1. Water Molecules Tend to Stick
together. Figure 2.7 Cohesion among
water molecules (p. 23).
• Due to hydrogen
bonding, water
molecules can
move from a plant’s
roots to its leaves
2. Water’s hydrogen bonds moderate
temperature
Water is able to absorb a great deal of heat energy
without a large increase in temperature and as it
cools, a slight drop in temperature releases a large
amount of heat
3. Evaporative cooling.
A water molecule takes a large
amount of energy with it when
it evaporates This leads to
evaporative cooling
4. Water is a versatile solvent
• Solutes whose charges or polarity allow
them to stick to water molecules dissolve in
water
– They form
aqueous
solutions
Na+
–
Na+
–
+
Cl–
+
+
–
Cl–
–
+
Ions in
solution
–
Salt
crystal
INTRODUCTION TO ORGANIC
COMPOUNDS AND THEIR POLYMERS
• Life’s structural and functional diversity results
from a great variety of molecules.
• In addition to water, all other biological molecules
are organic or carbon based molecules.
• A carbon atom forms four covalent bonds and it
can join with other carbon atoms to make chains
or rings
Structural Ball-and-stick Space-filling
formula
model
model
Methane
The 4 single bonds of carbon point to the corners of a tetrahedron.
Life’s molecular diversity is based on the
properties of carbon
• A carbon atom forms four covalent bonds and it can
join with other carbon atoms to make chains or rings.
Carbon skeletons vary in many ways .
¾Organic molecules are
characterized by having a
central “backbone” made of
atoms of carbon linked to
each other like a “chain” of
carbon atoms. In addition,
other atoms can link to the
carbon backbone
• Carbon skeletons vary in many ways
Ethane
Propane
Carbon skeletons vary in length.
Butane
Isobutane
Skeletons may be unbranched or branched.
1-Butene
2-Butene
Skeletons may have double bonds, which can vary in location.
Cyclohexane
Benzene
Skeletons may be arranged in rings.
Figure 3.1, bottom part
• Organic molecules are characterized by having
a central “backbone” made of atoms of carbon
linked to each other like a “chain” of carbon
atoms. Other atoms can link to the carbon
backbone
• There are 4 main types of biomolecules:
Carbohydrates
Lipids
Proteins
Nucleic Acids.
Chemical reactions rearrange
matter
• In a chemical reaction:
– reactants interact
– atoms rearrange
– products result
2 H2
+
O2
→
2 H2O
– Living cells carry out thousands of chemical
reactions that rearrange matter in significant
ways
Beta-carotene
Figure 2.17B
Vitamin A
(2 molecules)