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MODULE 3
STUDY GUIDE
Lesson 1
EARLY IDEAS ABOUT MATTER
• Dalton’s atomic theory
• Democritus was the first person to propose the existence of atoms.
• According to Democritus, atoms are solid, homogeneous, and
indivisible.
• Aristotle did not believe in the existence of atoms.
• Dalton revised the ideas of Democritus based on the results of
scientific research.
Lesson 2
DEFINING THE ATOM
• atom
• cathode ray
• electron
• nucleus
• proton
• neutron
• An atom is the smallest particle of an element that maintains the
properties of that element.
• Electrons have a 1
-
charge, protons have a 1
+
charge, and
neutrons have no charge.
• An atom consists mostly of empty space surrounding the nucleus.
Lesson 3
HOW ATOMS DIFFER
• atomic number
• isotope
• mass number
• atomic mass unit (amu)
• atomic mass
• The atomic number of an atom is given by its number of protons.
The mass number of an atom is the sum of its neutrons and
protons.
• Atoms of the same element with different numbers of neutrons
are called isotopes.
• The atomic mass of an element is a weighted average of the
masses of all of its naturally occurring isotopes.
Lesson 4
UNSTABLE NUCLEI AND RADIOACTIVE DECAY
• radioactivity
• radiation
• nuclear reaction
• radioactive decay
• alpha radiation
• alpha particle
• nuclear equation
• beta radiation
• beta particle
• gamma ray
• The radioactive decay of unstable nuclei involves the release of
energy.
• There are three types of radiation: alpha (charge of 2
+
), beta
(charge of 1
-
) and gamma (no charge).
• The neutron-to-proton ratio of an atom’s nucleus determines its
stability.
atomic number
=
number of protons
=
number of electrons
mass number
=
atomic number
+
number of neutrons
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Module 3 • Study Guide