Atoms And Isotopes (68)

The Atom Atomic Number and Mass Number Isotopes LecturePLUS Timberlake

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Atomic Theory

Atoms are building blocks of elements Similar atoms in each element Different from atoms of other elements Two or more different atoms bond in simple ratios to form compounds LecturePLUS Timberlake

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Subatomic Particles Particle

Symbol

Charge

Relative Mass

Electron

e-

1-

0

Proton

p+

+

1

Neutron

n

0

1

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Location of Subatomic Particles 10-13 cm electrons protons nucleus

10-8 cm

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neutrons

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Atomic Number Counts the number of protons in an atom

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Periodic Table Represents physical and chemical behavior of elements Arranges elements by increasing atomic number Repeats similar properties in columns known as chemical families or groups

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Periodic Table 1

2

3

4

5

6

7

8

11 Na

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Atomic Number on the Periodic Table Atomic Number

Symbol

11

Na LecturePLUS Timberlake

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All atoms of an element have the same number of protons 11 protons

Sodium

11

Na LecturePLUS Timberlake

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Learning Check AT 1 State the number of protons for atoms of each of the following: A. Nitrogen 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur 1) 32 protons

2) 16 protons

C. Barium 1) 137 protons 2) 81 protons LecturePLUS Timberlake

3) 6 protons 3) 56 protons 10

Solution AT 1 State the number of protons for atoms of each of the following: A. Nitrogen 2) 7 protons B. Sulfur 2) 16 protons C. Barium 3) 56 protons LecturePLUS Timberlake

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Number of Electrons

An atom is neutral The net charge is zero Number of protons = Number of electrons Atomic number = Number of electrons

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Mass Number

Counts the number of protons and neutrons in an atom

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Atomic Symbols Show the mass number and atomic number Give the symbol of the element mass number 23

atomic number

Na

sodium-23

11

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More Atomic Symbols

16

31

O 8

8 p+ 8n 8 e-

65

P

Zn

15

30

15 p+ 16 n LecturePLUS 15 e- Timberlake

30 p+ 35 n 30 e-

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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 35 17

Cl

chlorine - 35

37 17

Cl

chlorine - 37

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Learning Check AT 2 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.

C

C

C

12

13

14

6

6

6

#P _______

_______

_______

#N _______

_______

_______

_______

_______

#E _______

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Solution AT 2 C

C

C

12

13

14

6

6

6

#P __6___

_ 6___

___6___

#N __6___

_ _7___

___8___

#E __6___

_ 6___

___6___

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Learning Check AT 3 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 LecturePLUS Timberlake 19

Solution AT 3 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 LecturePLUS Timberlake

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Learning Check AT 4 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-

___________

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Solution AT 4 O

16

A. 8 p+, 8 n, 8 eB. 17p+, 20n, 17e-

8

17

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

Cl

37

107

Ag

47 LecturePLUS Timberlake

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Learning Check AT 5 An atom has 14 protons and 20 neutrons. A. Its atomic number is 1) 14 2) 16 3) 34 B. Its mass number is 1) 14 2) 16

3) 34

C. The element is 1) Si 2) Ca

3) Se

D. Another isotope of this element is 1)

34

X

16

14

2)

34

X

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14

3)

36

X 23

Solution AT 5 An atom has 14 protons and 20 neutrons. A. It has atomic number 1) 14 B. It has a mass number of 3) 34 C. The element is 1) Si D. Another isotope of this element would be

3) 36X 14

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Masses of Atoms A scale designed for atoms gives their small atomic masses in atomic mass units (amu) An atom of 12C was assigned an exact mass of 12.00 amu Relative masses of all other atoms was determined by comparing each to the mass of 12 C An atom twice as heavy has a mass of 24.00 amu. An atom half as heavy is 6.00 amu. 25 LecturePLUS Timberlake

Atomic Mass

Na 22.99

Listed on the periodic table Gives the mass of “average” atom of each element compared to 12C Average atom based on all the isotopes and their abundance % Atomic mass is not a whole number LecturePLUS Timberlake

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Learning Check AT6 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A. calcium

__________

B. aluminum

__________

C. lead

__________

D. barium

__________

E. iron

__________

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Solution AT6 Using the periodic table, specify the atomic mass of each element (round to the tenths place): A. calcium

_40.1 amu _

B. aluminum

_27.0 amu _

C. lead

_207.2 amu_

D. barium

_137.3 amu_

E. iron

_55.8 amu__

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Calculating Atomic Mass Percent(%) abundance of isotopes Mass of each isotope of that element Weighted average = mass isotope1(%) + mass isotope2(%) + … 100

100

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Atomic Mass of Magnesium Isotopes 24 Mg =

Abundance 78.70%

Mg

=

25.0 amu

10.13%

Mg

=

26.0 amu

11.17%

25 26

Mass of Isotope 24.0 amu

Atomic mass (average mass) Mg = 24.3 amu

Mg 24.3

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Learning Check AT7 Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the atomic mass of gallium? LecturePLUS Timberlake

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Solution AT7 Ga-69

68.9 amu x

60.2

=

41.5 amu for

69

Ga

28.2 amu for

71

Ga

100 Ga-71 (%/100)

70.9 amu x 39.8 100

=

Atomic mass Ga =

69.7 amu

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Finding An Isotopic Mass A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

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Assign X and Y values: X = % 10B Y = % 11B Determine Y in terms of X X + Y = 100 Y = 100 - X Solve for X: X (10.0) + (100 - X )(11.0) 100 100

= 10.8

Multiply through by 100 10.0 X + 1100 - 11.0X = 1080 LecturePLUS Timberlake

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Collect X terms 10.0 X - 11.0 X

=

1080 - 1100

- 1.0 X = -20 X

=

-20 - 1.0

=

Y = 100 - X % 11B = 100 - 20% =

20 %

10

B

80% 11B

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Learning Check AT8 Copper has two isotopes 63Cu (62.9 amu) and 65Cu (64.9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass) 1) 30%

2) 70%

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3) 100%

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Solution AT8 2) 70% Solution 62.9X + 6490 = 64.9X = 6350 -2.0 X = -140 X = 70% LecturePLUS Timberlake

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