Elements are different because they contain different numbers of protons

4.3 Distinguishing Among Atoms > Atomic Number Elements are different because they contain different numbers of protons. The atomic number of an e...
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Distinguishing Among Atoms

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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. Slide 6 of 52 © Copyright Pearson Prentice Hall

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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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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. Slide 13 of 52 © Copyright Pearson Prentice Hall

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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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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. Slide 19 of 52 © Copyright Pearson Prentice Hall

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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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Atomic Mass

It is useful to to compare the relative masses of atoms to a standard reference isotope. Carbon12 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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Atomic Mass

Some Elements and Their Isotopes

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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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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. Slide 28 of 52 © Copyright Pearson Prentice Hall

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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. Slide 35 of 52 © Copyright Pearson Prentice Hall

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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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The Periodic Table—A Preview

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

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

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The Periodic Table—A Preview

A Period

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The Periodic Table—A Preview

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

• Elements within a group have similar chemical and physical properties.

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The Periodic Table—A Preview

A Group or Family

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