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CHEMISTRY
Basic Concepts
Types of Reactions
A world of atoms
2,400 years ago, Democritus proposed
That the world is made of
atoms. The word atom is
Greek for “not breakable.”
(learn more)
In the early 1800’s John Dalton
revived atomic theory. He argued
that chemical reactions were the
rearrangement of atoms.
Democritus
from Essays on
Physiognomy.
By John Caspar
Lavater, trans. Henry
Hunter,
London, 1789 [vol I]
book containing 4
engraved illustrations by
Blake
Acquired at unknown
date
National Gallery of
Victoria
Modern Atoms
Today, we believe
atoms consist of a
small, massive,
positively charged
nucleus orbited by
light, negatively
charged electrons.
The negative electrons are attracted to the positive
nucleus and orbit around it. It is surprising that the part of
the atom that accounts for all its mass (the nucleus)
accounts for almost none of its volume.
The Nucleus
The nucleus (plural nuclei) is made of two different
particles: the positively charged proton and the
neutral neutron.
Positively charged protons repel one another. A
new force (the strong force) is needed to hold them
and the neutrons together in the nucleus (learn
more).
Electron Energy Levels
The electrons orbiting
around the nucleus
do so in discrete
orbits. Each orbit has
a specific energy
level. The farther out
the orbit, the higher
its energy.
Ions
• Atoms are neutral: they have an equal number of positive
protons and negative electrons.
• Atoms can become charged either by gaining or losing an
electron.
• Ions are indicated with a (+) or (-) sign
The Periodic Table
All known elements are listed in the Periodic Table. Each
element in a column on the periodic table has a similar
arrangement of outer electrons. This means they take
part in similar chemical reactions. online periodic table
Isotopes
The periodic table on the previous slide lists the atomic
number and atomic mass of each element.
Atomic Number = number of protons
Atomic Mass = # of protons + # of neutrons
• Notice that the atomic mass is not always a whole
number. It’s a weighted average.
• Some atoms of an element have different numbers of
neutrons.
• These atoms have different atomic masses and are
called isotopes.
Molecules
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H + H  H2
Sometimes when atoms bump into one
another, their outer electrons interact –
hooking the atoms together and forming a
molecule. (learn more)
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O + H + H  H2O
Types of Chemical Reactions
(all of these happen in space!!)
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Combination
Decomposition
Ionization
Radiative Recombination
Single Replacement
Negative Ion Reaction
Charge Transfer
Double Replacement
Combination
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C + O  CO
Decomposition
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SiO  Si + O
Ionization
(+)
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Na  Na+ + e-
Radiative Recombination
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H+ + e-  H
Single Replacement
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HCl + Na  NaCl + H
Negative Ion Reaction
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Cl- + Cl  Cl2
+
e-
Note: Cl2 has not been detected in space
Charge Transfer
(+)
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SO + H+  SO+ + H
Double Replacement
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CH + NO  CO + NH