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Atoms and Molecules
Macromolecule –a Protein
Caffeine molecule
The atom
• Neutral in charge.
• Composed of nucleus
with protons (+) and
neutrons (0).
• Electrons (-) found in
energy levels around
the nucleus.
• Atoms are most stable
when outer (valence)
energy level is full.
Lithium: Atomic # = 3, Atomic mass = 6
• Composed of atoms of
two or more elements.
• Held together by
chemical bonds.
• Chemical bonds require
energy to form.
• Chemical bonds result
from outer electrons
(valence electrons)
Methane gas molecule CH4
Remember: elements are specific types of atoms. The atomic # (# of
protons) determines the identify of an atom. i.e. Hydrogen has 1 proton.
Types of bonds
Water: two hydrogen atoms
plus an oxygen atom.
• Covalent bonds
– Two or more atoms share electrons.
– Example: water
• Ionic bonds
– Formed when electrons are
– Atoms become charged (ions)
– Opposite charged ions attract each
– Example: salt
Salt: one chlorine atom
plus one sodium atom.
Water: a special molecule
• Water is the most
common molecule on
Earth & in living
• Chemistry of living
organisms takes
place water.
Structure of The Water Molecule
• H20 is polar: it has
a negative end and
a positive end.
– Oxygen is negative
– Hydrogen is
– Polarity makes
water a good
Hydrogen Bonds
• Water molecules
are attracted to
each other.
• (-) oxygen is
attracted to (+)
• The attraction is
called a hydrogen
Hydrogen bonds are very weak
Cohesion & adhesion
• Cohesion: Molecules of
the same type are
attracted to each
– Surface tension is a
result of cohesion.
• Adhesion: Molecules of
different types are
attracted to each
– Plants move water up
stems in part due to
High heat capacity of water
• Heat capacity is the amount of
energy it take to raise the
temperature of a substance 1°C.
• Water must gain or lose a lot of
energy for its temperature to
• Results in stable aquatic
environment & the internal
environment of cells.
Note: aquatic means water, the ocean is an
aquatic environment.
• Ability to work or cause
• Energy is never lost, it
only changes form.
• Different forms of
– Chemical
– Thermal
– Mechanical
– electrical
Chemical Reactions
Reactions have:
• Reactants – starting
• Products – ending chemicals
2 H2O2 ---> 2 H2O + O2
Reduction-Oxidation Reactions
• Don’t Panic!
• This is a fancy way to talk about electron
transfers between products and reactants
• Oxidation: A substance gives up an electron and
becomes more positive
• Reduction: A substance gains an electron and
becomes more negative
To get a deeper understanding of this
concept view this series of videos on the
Khan Academy website:
Suggested Summary
When writing the summary for this lecture contrast the
following pairs:
Atom/ element
Molecule/ compound
Ionic/ covalent
Energy/ matter
Reactant/ product
Reduction/ oxidation