Transcript Symbols of Elements

Chapter 4 Atoms and
Elements
4.3
The Atom
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Dalton’s Atomic Theory
Atoms
• are tiny particles of matter
• of each element are
similar and different from
atoms of other elements
• of two or more different
elements combine to form
compounds
• are not created or
destroyed in a reaction
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Subatomic Particles
Atoms contains subatomic particles:
• protons have a positive (+)
charge
• electrons have a negative (-)
charge
• like charges repel and unlike
charges attract
• neutrons are neutral
Like charges repel, and unlike
charges attract.
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Basic Chemistry
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Thomsen’s “Plum Pudding”
Model of the Atom
J.J.Thomsen
• discovered that cathode rays
were streams of small
negatively charged particles
called electrons
• proposed the “plum pudding”
model of an atom in which
protons and electrons were
distributed throughout the
atom
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Basic Chemistry
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Rutherford’s Gold-Foil
Experiment
In Rutherford’s gold-foil experiment,
• positively charged particles were aimed at
atoms of gold
• most went straight through the foil
• only a few were deflected
• conclusion: There must be a small, dense,
positively charged nucleus in the atom that
deflects positive particles that come close
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Basic Chemistry
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Rutherford’s Gold-Foil
Experiment
Positive particles moving toward atoms of gold are deflected from their path
by the positive charges of the gold atoms.
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Basic Chemistry
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Structure of the Atom
An atom consists
• of a nucleus that contains protons and neutrons
• of electrons in the large empty space around the
nucleus
In an atom, the protons and
neutrons are in the nucleus,
whereas the electrons are
contained in the large space
outside the nucleus.
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Atomic Mass Scale
On the atomic mass scale for subatomic
particles,
1 atomic mass unit (amu) is equal to 1/12 of
the mass of the carbon-12 atom
a proton has a mass of 1.007 amu
a neutron has a mass of about 1.008 amu
an electron has a very small mass of
0.00055 amu
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Basic Chemistry
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Particles in the Atom
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Basic Chemistry
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