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Atoms and Elements

Isotopes and Atomic Mass

24Mg 25Mg 26Mg 12 12 12

GLTSBM

A Presentation byDEEPIKA

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Isotopes Are atoms of the same element that have different

mass numbers. Have the same number of protons, but different

numbers of neutrons.

Isotopes

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A nuclear symbol Represents a particular atom of an element. Gives the mass number in the upper left corner and

the atomic number in the lower left corner. Example: An atom of sodium with atomic number

11 and a mass number 23 has the following atomic symbol:

mass number 23 Na atomic number 11

Nuclear Symbol

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For an atom, the nuclear symbol gives the number of Protons (p+) Neutrons (n) Electrons (e-)

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-

Nuclear Symbols

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

12C 13C 14C 6 6 6

protons ______ ______ ______ neutrons ______ ______ ______ electrons ______ ______ ______

Learning Check

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12C 13C 14C 6 6 6

protons 6 p+ 6 p+ 6 p+

neutrons 6 n 7 n 8 nelectrons 6 e- 6 e- 6 e-

Solution

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Write the nuclear symbols for atoms with the following subatomic particles:A. 8 p+, 8n, 8e- ___________

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

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

Learning Check

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16OA. 8p+, 8n, 8e- 8

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

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

Solution

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Learning Check

1. Which of the following pairs are isotopes of the same element?

2. In which of the following pairs do both atoms have 8 neutrons? A. 15X 15X 8 7

B. 12X 14X 6 6

C. 15X 16X 7 8

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Solution

B. 12X 14X 6 6

Both nuclear symbols represent isotopes of carbon with six protons each, but one has 6 neutrons and the other has 8.

C. 15X 16X 7 8

An atom of nitrogen (7) and an atom of oxygen (8) each have 8 neutrons.

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Isotopes of Magnesium

In naturally occurring magnesium, there are three isotopes.

24Mg 25Mg 26Mg 12 12 12

Isotopes of Mg

Atomic Mass 23.99 24.98 25.98

% abundance 78.70 10.13 11.17

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Isotopes of Sulfur

A sample of naturallyoccurring sulfur containsseveral isotopes with thefollowing abundancesIsotope % abundance32S 95.02 33S 0.7534S 4.2136S 0.02

32S, 33S, 34S, 36S16 16 16 16

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Atomic Mass

The atomic mass of an element Is listed below the symbol of each

element on the periodic table. Gives the mass of an “average” atom of

each element compared to 12C. Is not the same as the mass number.

Na22.99

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Some Elements and Their Atomic Mass Most elements have two or more isotopes that contribute to the atomic mass of that element.

TABLE 2.9

32.07 amu

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Atomic Mass for Cl

The atomic mass of chlorine is Based on all naturally

occurring Cl isotopes. Not a whole number. The weighted average

of 35Cl and 37Cl.

Copyright © 2007 by Pearson Education, Inc.Publishing as Benjamin Cummings

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Using the periodic table, give the atomic mass ofeach element:

A. calcium __________

B. aluminum __________

C. lead __________

D. barium __________

E. iron __________

Learning Check

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Using the periodic table, give the atomic mass ofeach element:

A. calcium 40.08 amu

B. aluminum 26.98 amu

C. lead 207.2 amu

D. barium 137.3 amu

E. iron 55.85 amu

Solution

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The End

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