The Atom Atomic Number and Mass Number Isotopes

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2

16 31 65

O P Zn

8 15 30

8 p+ 15 p+ 30 p+

8 n 16 n 35 n

8 e- 15 e- 30 e-

Slide 14

Isotopes

Atoms with the same number of protons, but different numbers of neutrons.

Atoms of the same element (same atomic number) with different mass numbers

Isotopes of chlorine

35Cl 37Cl

17 17

chlorine - 35 chlorine - 37

Slide 15

Learning Check

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C

6 6 6

#p _ _ _

#n _ _ _

#e _ _ _

Slide 16

Solution

12C 13C 14C

6 6 6

#p 6 6 6

#n 6 7 8

#e 6 6 6

Slide 17

Learning Check

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30 2) 35 3) 65

B. Number of neutrons in the zinc atom

1) 30 2) 35 3) 65

C. What is the mass number of a zinc isotope

with 37 neutrons?

1) 37 2) 65 3) 67

Slide 18

Solution

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30

B. Number of neutrons in the zinc atom

2) 35

C. What is the mass number of a zinc isotope

with 37 neutrons?

3) 67

Slide 19

Learning Check

Write the atomic symbols for atoms with the following:

A. 8 p+, 8 n, 8 e- _

B. 17p+, 20n, 17e- _

C. 47p+, 60 n, 47 e- _

Slide 20

Solution

16O

A. 8 p+, 8 n, 8 e- 8

B. 17p+, 20n, 17e- 37Cl

17

C. 47p+, 60 n, 47 e- 107Ag

47

Slide 21

Atomic Mass on the Periodic Table

11

Na

22.99

Atomic Number

Symbol

Atomic Mass

Slide 22

Atomic Mass

Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.

Slide 23

Example of an Average Atomic Mass

Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine.

35 x 75.5 = 26.4

100

35.5

37 x 24.5 = 9.07

100