Chapter 4 Notes
Key Concepts:
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How did Democritus describe atoms?
Democritus believed that atoms were indivisible and indestructible.
How did John Dalton further Democritus’s ideas on atoms?
By using experimental methods, Dalton transformed Democritus’s ideas on atoms into a
scientific theory.
What instruments are used to observe individual atoms?
Despite their small size, individual atoms are observable with instruments such as scanning
tunneling microscopes.
Vocabulary
1. Atom- is the smallest particle of an element that retains its identity in a chemical reaction.
2. Dalton’s Atomic Theory- the first theory to relate chemical changes to events at the atomic
level.
I.
Defining the Atom
A. Early Models of the Atom
o Summary
1. Democritus’s Atomic Philosophy
1. Summary
2. Dalton’s Atomic Theory
2. Summary
B. Sizing Up the Atom
o Summary
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Key Concepts:
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What are three kinds of subatomic particles?
Three kinds of subatomic particles are electrons, protons, and neutrons.
How can you describe the structure of the atom?
In the nuclear atom, the protons and neutrons are located in the nucleus. The electrons are
distributed around the nucleus and occupy almost all the volume of the atom.
Vocabulary
1. Electrons- are negatively charged subatomic particles.
2. Cathode Ray- a stream of electrons produced at the negative electrode (cathode) of a tube
containing a gas at low pressure.
3. Protons- a positively charged subatomic particle found in the nucleus of an atom.
4. Neutrons- are subatomic particles with no charge but with a mass nearly equal to that of a
proton.
5. Nucleus- the tiny central core of an atom and is composed of protons and neutrons.
II.
Structure of the Nuclear Atom
A. Subatomic Particles
o Summary
o Electrons
 Summary
2. Protons and Neutrons
 Summary
B. The Atomic Nucleus
o Summary
1. Rutherford’s Gold-Foil Experiment
 Summary
2. The Rutherford Atomic Model
 Summary
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Key Concepts:
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What makes one element different from another?
Elements are different because they contain different numbers of protons.
How do you find the number of neutrons in an atom?
The number of neutrons in an atom is the difference between the mass number and atomic
number.
How do isotopes of an element differ?
Because isotopes of an element have different numbers of neutrons, they also have different
mass numbers.
How do you calculate the atomic mass of an element?
To calculate the atomic mass of an element, multiply the mass of each isotope by its natural
abundance, expressed as a decimal, and then add the products.
Why is a periodic table useful?
To calculate the atomic mass of an element, multiply the mass of each isotope by its natural
abundance, expressed as a decimal, and then add the products.
Vocabulary:
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6.
Atomic Number- the number of protons in the nucleus of an atom of that element.
Mass Number- the total number of protons and neutrons in an atom
Isotopes- atoms that have the same number of protons but different numbers of neutrons
Atomic Mass Unit (amu)- one twelfth of the mass of a carbon-12 atom
Atomic Mass- the weighted average of the masses of the isotopes of an element
Periodic Table- an arrangement of elements in which the elements are separated into groups
based on a set of repeating properties.
7. Period- each horizontal row of the periodic table
8. Group- each vertical column of the periodic table
III.
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E.
Distinguishing Among Atoms
Atomic Number
o Summary
Mass Number
o Summary
Isotopes
o Summary
Atomic Mass
o Summary
The Periodic Table-A Preview
o Summary
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