1. © Copyright Pearson Prentice Hall Connecting to Your World Slide 1 of 52 Distinguishing Among Atoms Just as apples come in different varieties, a chemical element can come in different “varieties” called isotopes. 4.3

2. © Copyright Pearson Prentice Hall Distinguishing Among Atoms > Slide 2 of 52 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.

3. Slide 3 of 52 © Copyright Pearson Prentice Hall > 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. 4.3

4. Slide 4 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms Mass Number Au is the chemical symbol for gold. 4.3

5. © Copyright Pearson Prentice Hall Distinguishing Among Atoms > Slide 5 of 52 Isotopes How do isotopes of an element differ? 4.3

6. Slide 6 of 52 © Copyright Pearson Prentice Hall > 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.

7. Slide 7 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms Isotopes Despite these differences, isotopes are chemically alike because they have identical numbers of protons and electrons. 4.3

8. Slide 8 of 52 © Copyright Pearson Prentice Hall > 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. 4.3

9. Slide 9 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms Atomic Mass Some Elements and Their Isotopes 4.3

10. Slide 10 of 52 © Copyright Pearson Prentice Hall > 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. 4.3

11. Slide 11 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms Atomic Mass Weighted Average Mass of a Chlorine Atom 4.3

12. © Copyright Pearson Prentice Hall Distinguishing Among Atoms > Slide 12 of 52 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. 4.3

13. Slide 13 of 52 © Copyright Pearson Prentice Hall > 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

14. Slide 14 of 52 © Copyright Pearson Prentice Hall > 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). 4.3

15. Slide 15 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms The Periodic Table—A Preview The Periodic Table 4.3

16. Slide 16 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms 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. 4.3

17. Slide 17 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms The Periodic Table—A Preview A Period 4.3

18. Slide 18 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms 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. 4.3

19. Slide 19 of 52 © Copyright Pearson Prentice Hall > Distinguishing Among Atoms The Periodic Table—A Preview A Group or Family 4.3

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