Transcript Symbols of Elements

General, Organic, and
Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 3
Atoms and Elements
3.3
The Atom
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Lectures
Dalton’s Atomic Theory
Dalton theorized that Atoms
 are tiny particles of matter
too small to see,
 are able to combine with
other atoms to make
compounds, and
 are similar to each other for
each element and different
from atoms of other
elements.
A chemical reaction is the
rearrangement of atoms.
© 2013 Pearson Education, Inc.
Images of nickel atoms
are produced when nickel is magnified
millions of times by a scanning
tunneling microscope (STM). This
instrument generates an image of
the atomic structure.
Chapter 3, Section 3
2
Subatomic Particles
Atoms contain subatomic
particles such as
 Protons, which have a
positive (+) charge;
 electrons, which have a
negative (–) charge; and
 neutrons, which have no
charge.
Experiments show that like
charges repel and unlike
charges attract.
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Chapter 3, Section 3
3
Rutherford’s Gold-Foil
Experiment
In Rutherford’s gold-foil experiment, positively
charged particles were aimed at atoms of gold and
 most went straight through the atoms, but
 some were deflected only occasionally.
Conclusion:
There must be a small, dense, positively charged
nucleus in the atom that deflects positive particles
that come close.
© 2013 Pearson Education, Inc.
Chapter 3, Section 3
4
Rutherford’s Gold-Foil
Experiment
(a) Positive particles are aimed at a piece of gold foil. (b) Particles that come
close to the atomic nuclei of gold are deflected from their straight path.
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Chapter 3, Section 3
5
Structure of the Atom
An atom consists of
 a nucleus that
contains protons
and neutrons, and
 electrons in a
large, empty space
around the
nucleus.
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Chapter 3, Section 3
6
Atomic Mass Scale
On the atomic mass scale for subatomic particles,
1 atomic mass unit (amu) is defined as 1/12 of the mass
of the carbon-12 atom. Therefore,
 a proton has a mass of about 1 (1.007) amu.
 a neutron has a mass of about 1 (1.008) amu.
 an electron has a very small mass, 0.00055 amu.
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Chapter 3, Section 3
7
Particles in the Atom
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Chapter 3, Section 3
8
Learning Check
Identify each statement as describing a(n) proton,
neutron, or electron.
1. _____________
Found outside the nucleus
2. _____________
Has a positive charge
3. _____________
Is neutral
4. _____________
Found in the nucleus
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Chapter 3, Section 3
9
Solution
Identify each statement as describing a(n) proton,
neutron, or electron.
1. electron
Found outside the nucleus
2. proton
Has a positive charge
3. neutron
Is neutral
4. protons, neutrons
Found in the nucleus
© 2013 Pearson Education, Inc.
Chapter 3, Section 3
10