Download Chapter 4 Atoms and Elements

Chapter 4 Atoms and
Elements
1
Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Atoms: The Building Blocks
of Matter
A brick is the smallest
unit that has the
characteristics of a
brick wall.
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An atom is the smallest particle
that has the characteristics and
properties of an element. If you
split the atom, you no longer
have aluminum.
Structure
Atoms contain sub-atomic particles:
•  protons
•  electrons
•  neutrons
Atoms have two regions:
•  the nucleus is the small, dense
center that contains protons
and neutrons
•  the electron cloud is the large, less-dense outer region
that contains electrons and mostly empty space
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Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Identity
The number of protons in an atom determines its identity.
A beryllium atom has
4 protons.
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If a 5th proton is added the
atom has a new identity boron.
Atomic Charges
• 
• 
• 
• 
protons have a positive (+) charge
electrons have a negative (-) charge
neutrons are neutral and have no charge
neutral atoms have an equal number of protons
and electrons
•  ions are atoms that have an unequal number of
protons and electrons
•  an atom’s net charge = # of protons - # electrons
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Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Forces Acting in Atoms
Electrostatic Forces
•  like charges repel
and unlike charges
attract
•  exerts force in both
the nucleus and
electron cloud
•  neutrons are not
affected by these
forces because
they are neutral
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Basic Chemistry
Nuclear Forces
•  all the protons and
neutrons in the
nucleus are attracted
to each other
•  only exerts force in
the nucleus
Copyright © 2011 Pearson Education, Inc.
Stability
•  protons increase the
attractive nuclear force,
but they also increase
electrostatic repulsive force
•  neutrons increase the
attractive nuclear force
without increasing the
repulsive electrostatic force
•  neutrons increase the stability of the nucleus and the atom
as long as there are only a few more neutrons than protons
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Stability (cont’d)
•  the electron cloud has a
negative charge because it
only has electrons
•  the nucleus has a positive
charge because it only has
protons and neutrons
•  electrostatic forces keep the
negatively charged electrons
moving around the positively
charged nucleus
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Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Atomic Mass & Mass Number
Atomic mass and mass number are not the same.
Atomic mass is the atom’s actual mass
•  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
Mass number is the atom’s approximate mass
•  protons and neutrons have a mass number of 1
•  electrons have a mass number of 0
•  mass number = # of protons + # of neutrons
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Basic Chemistry
Copyright © 2011 Pearson Education, Inc.
Particles in the Atom
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Basic Chemistry
Copyright © 2011 Pearson Education, Inc.