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Chemistry 4.3
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Distinguishing Among Atoms
Just as apples come in different varieties, a chemical element can come in different “varieties” called isotopes.
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Distinguishing Among Atoms >
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4.3 Atomic Number
Atomic Number
What makes one element different from another?
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Distinguishing Among Atoms >
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4.3 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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>Distinguishing Among Atoms Atomic Number 4.3
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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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Mass Number
Mass Number
How do you find the number of neutrons in an atom?
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>Distinguishing Among Atoms 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 Mass Number
Au is the chemical symbol for gold.
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SAMPLE PROBLEM
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4.1
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SAMPLE PROBLEM
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4.1
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SAMPLE PROBLEM
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4.1
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SAMPLE PROBLEM
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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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Isotopes
Isotopes
How do isotopes of an element differ?
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>Distinguishing Among Atoms 4.3 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 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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Atomic Mass
Atomic Mass
How do you calculate the atomic mass of an element?
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>Distinguishing Among Atoms 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 Atomic Mass
Some Elements and Their Isotopes
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>Distinguishing Among Atoms 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 Atomic Mass
Weighted Average Mass of a Chlorine Atom
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Practice Problems
for Conceptual Problem 4.3
Problem Solving 4.21 Solve Problem 21 with the help of an interactive guided tutorial.
for Conceptual Problem 4.3
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Distinguishing Among Atoms >
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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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>Distinguishing Among Atoms 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%.
4.3
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SAMPLE PROBLEM
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SAMPLE PROBLEM
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4.2
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SAMPLE PROBLEM
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SAMPLE PROBLEM
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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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The Periodic Table—A Preview
The Periodic Table—A Preview
Why is a periodic table useful?
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>Distinguishing Among Atoms 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 The Periodic Table—A Preview
The Periodic Table
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