Distinguishing Among Atoms Mass Number

Chemistry 4.3

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4.3

Distinguishing Among Atoms

Connecting to Your World

Just as apples come in different varieties, a chemical element can come in different

“varieties” called isotopes.

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© Copyright Pearson Prentice Hall

4.3

Distinguishing Among Atoms > Atomic Number

Atomic Number

What makes one element different from another?

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4.3


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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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 > Mass Number

Mass Number

How do you find the number of neutrons in an atom?

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4.3

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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SAMPLE PROBLEM 4.1


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Practice Problems for Sample Problem 4.1


Solve

Problem 17 with the help of an interactive guided tutorial.


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4.3

Distinguishing Among Atoms > Isotopes

Isotopes

How do isotopes of an element differ?

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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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Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons.


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4.3

Distinguishing Among Atoms > Atomic Mass

Atomic Mass

How do you calculate the atomic mass of an element?

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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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4.3


Some Elements and Their Isotopes


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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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Weighted Average Mass of a Chlorine Atom


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Practice Problems for Conceptual Problem 4.3

for Conceptual Problem 4.3


Solve

Problem 21 with the help of an interactive guided tutorial .


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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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For example, carbon has two stable isotopes:

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Carbon-12, which has a natural abundance of

98.89%, and

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Carbon-13, which has a natural abundance of

1.11%.

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4.3

Distinguishing Among Atoms > The Periodic Table

—A Preview

The Periodic Table —A Preview

Why is a periodic table useful?

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—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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—A Preview

The Periodic Table


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—A Preview

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Each horizontal row of the periodic table is called a period .

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Within a given period, the properties of the elements vary as you move across it from element to element.

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—A Preview

A Period


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—A Preview

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Each vertical column of the periodic table is called a group , or family.

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Elements within a group have similar chemical and physical properties.

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—A Preview

A Group or Family


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Distinguishing Among Atoms > Concept Map


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End Show

Distinguishing Among Atoms Mass Number

Distinguishing Among Atoms

Atomic Number

Mass Number

Isotopes

Atomic Mass

The Periodic Table —A Preview

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Distinguishing Among Atoms Mass Number