Chemistry 4.3
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4.3
Distinguishing Among Atoms
Just as apples come in
different varieties, a
chemical element can
come in different
“varieties” called isotopes.
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Atomic Number
Atomic Number
What makes one element different from
another?
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Atomic Number
Elements are different because they
contain different numbers of protons.
The atomic number of an element is the
number of protons in the nucleus of an atom
of that element.
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Atomic Number
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Atomic Number
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Practice Problems for Conceptual Problem 4.1
Problem Solving 4.15 Solve
Problem 15 with the help of an
interactive guided tutorial.
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4.3
Distinguishing Among Atoms
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Mass Number
Mass Number
How do you find the number of neutrons
in an atom?
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Mass Number
The total number of protons and neutrons in an
atom is called the mass number.
The number of neutrons in an atom is
the difference between the mass
number and atomic number.
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Distinguishing Among Atoms
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Mass Number
Au is the chemical symbol for gold.
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SAMPLE PROBLEM 4.1
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SAMPLE PROBLEM 4.1
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SAMPLE PROBLEM 4.1
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SAMPLE PROBLEM 4.1
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Practice Problems for Sample Problem 4.1
Problem Solving 4.17 Solve
Problem 17 with the help of an
interactive guided tutorial.
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4.3
Distinguishing Among Atoms
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Isotopes
Isotopes
How do isotopes of an element differ?
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Distinguishing Among Atoms
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Isotopes
Isotopes are atoms that have the same number
of protons but different numbers of neutrons.
Because isotopes of an element have
different numbers of neutrons, they
also have different mass numbers.
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Distinguishing Among Atoms
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Isotopes
Despite these differences, isotopes are
chemically alike because they have identical
numbers of protons and electrons.
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Practice Problems for Conceptual Problem 4.2
Problem Solving 4.20
Solve Problem 20 with the help
of an interactive guided tutorial.
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4.3
Distinguishing Among Atoms
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Atomic Mass
Atomic Mass
How do you calculate the atomic mass
of an element?
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Distinguishing Among Atoms
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Atomic Mass
It is useful to to compare the relative masses of
atoms to a standard reference isotope.
Carbon-12 is the standard reference isotope.
Cabon-12 has a mass of exactly 12 atomic mass
units.
An atomic mass unit (amu) is defined as one
twelfth of the mass of a carbon-12 atom.
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Distinguishing Among Atoms
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Atomic Mass
Some Elements and Their Isotopes
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Distinguishing Among Atoms
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Atomic Mass
The atomic mass of an element is a weighted
average mass of the atoms in a naturally
occurring sample of the element.
A weighted average mass reflects both the mass
and the relative abundance of the isotopes as
they occur in nature.
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Distinguishing Among Atoms
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Atomic Mass
Weighted Average Mass of a Chlorine Atom
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Practice Problems for Conceptual Problem 4.3
for Conceptual Problem 4.3
Problem Solving 4.21 Solve
Problem 21 with the help of
an interactive guided tutorial.
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Atomic Mass
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.
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Atomic Mass
For example, carbon has two stable isotopes:
• Carbon-12, which has a natural abundance of
98.89%, and
• Carbon-13, which has a natural abundance of
1.11%.
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SAMPLE PROBLEM 4.2
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SAMPLE PROBLEM 4.2
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SAMPLE PROBLEM 4.2
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SAMPLE PROBLEM 4.2
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Practice Problems for Sample Problem 4.2
Problem Solving 4.24 Solve
Problem 24 with the help of an
interactive guided tutorial.
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Distinguishing Among Atoms
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The Periodic Table—A Preview
The Periodic Table—A Preview
Why is a periodic table useful?
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The Periodic Table—A Preview
A periodic table is an arrangement of elements
in which the elements are separated into groups
based on a set of repeating properties.
A periodic table allows you to easily
compare the properties of one element
(or a group of elements) to another
element (or group of elements).
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Distinguishing Among Atoms
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The Periodic Table—A Preview
The Periodic Table
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