4.1
Defining the Atom
> Early Models of the Atom
Early Models of the Atom
• An atom is the smallest particle of an element
that retains its identity in a chemical reaction.
• Philosophers and scientists have proposed
many ideas on the structure of atoms.
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4.1
Defining the Atom
> Early Models of the Atom
Democritus believed that atoms were
indivisible and indestructible.
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4.1
Defining the Atom
> Early Models of the Atom
By using experimental methods, Dalton
changed Democritus’s ideas on atoms
into a scientific theory.
The result was Dalton’s atomic theory
which has four main points.
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4.1
Defining the Atom
> Early Models of the Atom
1. All elements are composed of tiny indivisible
particles called atoms.
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4.1
Defining the Atom
> Early Models of the Atom
2. Atoms of the same element are identical.
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4.1
Defining the Atom
> Early Models of the Atom
3. Atoms of different elements can physically mix
together or can chemically combine in simple
whole-number ratios to form compounds.
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4.1
Defining the Atom
> Early Models of the Atom
4. Chemical reactions occur when atoms are
separated, joined, or rearranged. Atoms of one
element are never changed into atoms of
another element in a chemical reaction.
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Section 4.2
The Structure of the Nuclear Atom
Subatomic Particles
1.
Electrons are negatively charged subatomic particles
that surround the nucleus of the atom.
2.
Protons are positively charged subatomic particles and
are found within the nucleus of an atom.
3.
Neutrons are subatomic particles with no charge
(neutral). They are found within the nucleus of an
atoms.
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Section 4.2
Page 106:
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Section 4.3
Distinguishing Among Atoms
Atomic Number
Each element in the periodic table has a unique atomic
number.
The atomic number corresponds to the number of
protons in the nucleus.
For an element, the number of electrons will equal the
number of protons.
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Section 4.3
Mass Number
The mass number is the total number of protons
and neutrons in the nucleus.
Mass Number = protons + neutrons
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Sections 4.3
Isotopes
Isotopes are atoms that have the same number of
protons, but different numbers of neutrons.
Therefore, isotopes of the same element will have
different mass numbers.
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Section 4.3
Special notation is used to distinguish between
different isotopes:
12
6C
Carbon-12
13
6C
Carbon-13
Mass Number
Mass Number
Practice Questions: Page 112 # 17, 18.
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Section 4.3
Atomic Mass
•
The actual mass of an atom is measured in atomic
mass units (amu).
•
The atomic mass is found in the element’s square of
the periodic table.
•
The atomic mass is the weighted average mass of
the atom’s naturally occurring isotopes.
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Section 4.3
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Practice Questions:
Fill in the following table:
Element
Name
Mass
Number
Number e-
Number of p+
Number of n0
25
25
36
37
Shorthand
Carbon-12
Chlorine-35
Page 113 # 19, 20
Page 122 # 48, 49, 50
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