Distinguishing Among Atoms CN#2 Just as apples come in different varieties, a chemical element can come in different “varieties” called isotopes.

Atomic Number What makes one element different from another? 4.3

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 an atom. It is also the number of electrons.

Atomic Number

for Conceptual Problem 4.1 Problem Solving 4.15 Solve Problem 15 with the help of an interactive guided tutorial.

Mass Number How do you find the mass number of an atom? 4.3

Mass number = protons + neutrons 4.3 Mass Number The mass number is the total number of protons and neutrons in an atom. Mass number = protons + neutrons Neutrons = mass number - protons

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4.3 Atomic Number

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for Sample Problem 4.1 Problem Solving 4.17 Solve Problem 17 with the help of an interactive guided tutorial.

4.3 Isotopes Isotopes How do isotopes of an element differ?

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.

4.3 Isotopes Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons. Neon-20, neon-21, and neon-22 are three isotopes of neon, a gaseous element used in lighted signs. Comparing and Contrasting How are these isotopes different? How are they similar?

for Conceptual Problem 4.2 Problem Solving 4.20 Solve Problem 20 with the help of an interactive guided tutorial.

The Periodic Table—A Preview 4.3 The Periodic Table—A Preview The Periodic Table—A Preview Why is a periodic table useful?

The Periodic Table—A Preview 4.3 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).

The Periodic Table—A Preview 4.3 The Periodic Table—A Preview The Periodic Table Elements are arranged in the modern periodic table in order of atomic number. Interpreting Diagrams How many elements are in Period 2? In Group 2A?

The Periodic Table—A Preview 4.3 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.

The Periodic Table—A Preview 4.3 The Periodic Table—A Preview A Period

The Periodic Table—A Preview 4.3 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.

The Periodic Table—A Preview 4.3 The Periodic Table—A Preview A Group or Family

H B Si Ge As Sb Te Po At

4.3 Section Quiz 4.3.

1. Isotopes of an element have the same mass number. 4.3 Section Quiz 1. Isotopes of an element have the same mass number. different atomic numbers. the same number of protons but different numbers of neutrons. the same number of protons but different numbers of electrons. ANS: C PTS: 1 REF: p. 112 OBJ: 4.3.1

2. How many neutrons are in sulfur-33? 16 neutrons 33 neutrons 4.3 Section Quiz 2. How many neutrons are in sulfur-33? 16 neutrons 33 neutrons 17 neutrons 32.06 neutrons ANS: C PTS: 1 REF: p. 111 OBJ: 4.3.2

4.3 Section Quiz 3. If sulfur contained 90.0% sulfur-32 and 10.0% sulfur-34, its atomic mass would be 32.2 amu. 32.4 amu. 33.0 amu. 35.4 amu. ANS: A PTS: 1 REF: p. 116 OBJ: 4.3.3

Concept Map

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