Chapter 2
Atoms, Molecules,
and Ions
Atomic Theory of Matter
The theory that atoms
are the fundamental
building blocks of
matter reemerged in the
early nineteenth
century, championed by
John Dalton.
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Dalton's Postulates
Each element is
composed of
___________________
___________________
___________________
Dalton's Postulates
All atoms of a given
element are _________
___________________
in mass and other
properties, but the
atoms of one element
___________________
___________________
___________________
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Dalton's Postulates
Atoms of an element
are ________________
___________________
__________________
by chemical reactions;
atoms are neither
____________nor
____________in
chemical reactions.
Dalton's Postulates
Compounds are
formed when ________
___________________
____________; a given
compound always has
the same ___________
___________________
___________________
The total mass of substances present at the
end of a chemical process is _____________
____________________________________
____________________________________
Law of Conservation of Mass
The Electron
•Streams of negatively charged particles were found to
emanate from cathode tubes, causing fluorescence.
•J. J. Thomson is credited with their discovery (1897).
The Electron
Thomson measured the charge/mass ratio of
the electron to be 1.76 108 coulombs/gram
(C/g).
Millikan Oil-Drop Experiment
Once the charge/mass
ratio of the electron
was known,
determination of either
the charge or the mass
of an electron would
yield the other.
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Millikan Oil-Drop Experiment
Robert Millikan
(University of Chicago)
determined the charge
on the electron in
1909.
•Radioactivity is the ______________________
______________________________________
•It was first observed by Henri Becquerel.
•Marie and Pierre Curie also studied it.
Radioactivity
Radioactivity
•Three types of radiation were discovered by
Ernest Rutherford:
◦
_______________________
◦
_______________________
◦
_______________________
The Atom, circa 1900
•The prevailing theory
was that of the “plum
pudding” model, put
forward by Thomson.
•It featured ___________
____________________
____________________
____________________
________________
Discovery of the Nucleus
Ernest
Rutherford shot
particles at a
thin sheet of
gold foil and
observed the
pattern of
scatter of the
particles.
The Nuclear Atom
Since some particles
were deflected at
large angles,
_________________
_________________
________________.
The Nuclear Atom
•Rutherford
postulated _______
________________
________________
________________
________________
________________
•Most of the volume
of the atom is _____
________________
•Protons were discovered by Rutherford in
1919.
•Neutrons were discovered by James
Chadwick in 1932.
Other Subatomic Particles
Subatomic Particles
•Protons and electrons are the only particles that
have a __________.
•Protons and neutrons have essentially the same
___________.
•The mass of an electron is so small _________
____________________.
Symbols of Elements
Elements are symbolized by one or two
letters.
Symbols of Elements
All atoms of the same element have the
____________________________, which is
called the ___________________________.
Symbols of Elements
The _____________________of an atom in
atomic mass units (amu) is the ___________
____________________________________
Isotopes
•Isotopes are __________________________
_____________________________________
•Isotopes have different numbers of ________.
Atomic Mass
Atomic and
molecular masses
can be measured
with great accuracy
using a mass
spectrometer.
•Because in the real world we use large amounts
of atoms and molecules, we use average
masses in calculations.
•Average mass is calculated from ___________
______________________________________
______________________________________
______________________________________
Average Mass
Periodic Table
•The periodic
table is a
systematic catalog
of the elements.
•Elements are
arranged _______
_______________
_____________
Periodic Table
•The rows on the
periodic chart are
_____________.
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Extremely small
particles called atoms
