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The Structure of an Atom
A key discovery leading to the current model of the atom was that
atoms contain particles that have electric charges. A particle’s charge
can be either positive or negative. Particles with the same charge repel
each other—they are pushed apart. Particles with different charges
attract each other—they are drawn toward each other.
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Learn more about
the atom.
Atoms are composed of three types of particles—protons, neutrons,
and electrons. A proton is a positively charged particle. A neutron is
an uncharged particle. The neutron has approximately the same mass
as a proton. Protons and neutrons are grouped together in the atom’s
center. This combination of protons and neutrons is called the nucleus
of the atom. Because protons are the only particles in the nucleus that
have an electric charge, the nucleus is positively charged. Electrons are
negatively charged particles that move around outside the nucleus.
VOCABULARY
Remember to make a
frame for neutron, proton, and electron and for
other vocabulary terms.
We can only guess where electrons are at any time. Because we can’t
locate any one electron with certainty, we say that electrons move about
in an electron cloud. We do know that each electron in the electron
cloud has a certain amount of energy. This energy keeps it moving
about the nucleus. The energy keeps the negative electron from falling
into the positive nucleus. We also know that electrons with similar
amounts of energy are grouped together in shells. Each shell can hold
only a certain number of electrons that have about the same energy.
An electron may jump from one shell to the next if enough energy is
added to it.
The Atomic Model
Atoms are made of protons, neutrons, and electrons.
proton
+
+
+
+
+
+
+
Particle Charges and Mass
+ +
+
neutron
FPO
Particle
Relative Relative
Mass
Charge
nucleus
Electron
1
–1
The nucleus has an
overall positive charge.
Proton
2000
+1
Neutron
2000
0
electron cloud
The electron cloud has
a negative charge.
Which part of the atom has a negative charge?
Chapter 7: Atomic Structure and the Periodic Table 201
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