The Atomic Number and Mass Number Isotopes Take

The Atomic Number and Mass Number Isotopes (Take out your Periodic Tables) Lecture. PLUS Timberlake 1

EQ’s 1. What is the Atomic Theory? 2. What is an atom and how are its components arranged? 3. What is an isotope and how are neutrons related to isotopes? 4. How are isotopes and an element’s average atomic mass related? Lecture. PLUS Timberlake 2

Atomic Theory l Atoms are building blocks of elements l Each element has similar atoms l Different from atoms of other elements l Two or more different atoms bond in simple ratios to form compounds Lecture. PLUS Timberlake 3

Subatomic Particles Particle Symbol Charge Relative Mass Electron e- 1 - 0 Proton p+ 1+ 1 Neutron n 0 1 Lecture. PLUS Timberlake 4

Location of Subatomic Particles 10 -13 cm electrons protons nucleus 10 -8 cm Lecture. PLUS Timberlake neutrons 5

Atomic Number Represents the number of protons in an atom Lecture. PLUS Timberlake 6

Periodic Table l Represents physical and chemical behavior of elements l Arranges elements by increasing atomic number l Repeats similar properties in columns known as chemical families or groups Lecture. PLUS Timberlake 7

Periodic Table 1 2 3 4 5 6 7 8 11 Na Lecture. PLUS Timberlake 8

Atomic Number on the Periodic Table Atomic Number Symbol 11 Na Lecture. PLUS Timberlake 9

All atoms of an element have the same number of protons 11 protons Sodium 11 Na Lecture. PLUS Timberlake 10

Learning Check AT 1 State the number of protons for atoms of each of the following: A. Nitrogen (N) 1) 5 protons 2) 7 protons 3) 14 protons B. Sulfur (S) 1) 32 protons 2) 16 protons 3) 6 protons C. Barium (Ba) 1) 137 protons 2) 81 protons Lecture. PLUS Timberlake 3) 56 protons 11

Number of Electrons l An atom is neutral l The net charge is zero l Number of protons = Number of electrons l Atomic number = Number of electrons Lecture. PLUS Timberlake 12

Mass Number Represents the number of protons and neutrons in an atom Lecture. PLUS Timberlake 13

Isotopes l Atoms with the same number of protons, but different numbers of neutrons. l Atoms of the same element (same atomic number) with different mass numbers Isotopes of chlorine 35 Cl 37 Cl 17 17 chlorine - 35 Lecture. PLUS chlorine - 37 Timberlake 14

ISOTOPIC NOTATION A Z X A = mass number (the total number of protons + neutrons) Z = atomic number (the total number of protons) X = element symbol

Atomic Symbols l Show the mass number and atomic number l Give the symbol of the element mass number 23 Na atomic number sodium-23 11 Lecture. PLUS Timberlake 16

READING ISOTOPIC NOTATION 46 21 Sc 46 = mass number (the total number of protons (21) 21 + neutrons (25)) 25 21 = atomic number (the total number of protons (21)) 21 Sc = element symbol In a neutral atom, the number of electrons (21) is equal to the number of protons.

More Atomic Symbols 16 O 8 31 P 15 65 8 p+ 8 n 8 e- 15 p+ 16 n 15 e- 30 p+ 35 n 30 e- Lecture. PLUS Timberlake 30 Zn 19

Learning Check AT 2 Naturally occurring carbon consists of three isotopes, 12 C, 13 C, and 14 C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12 C 13 C 14 C 6 6 #P _______ #N _______ _______ #E _______ Lecture. PLUS Timberlake 6 20

Solution AT 2 12 C 6 13 C 6 14 C 6 #P __6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ ___6___ Lecture. PLUS Timberlake 21

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 Lecture. PLUS Timberlake 22

Learning Check AT 4 Write the atomic symbols for atoms with the following: A. 8 p+, 8 n, 8 e. B. 17 p+, 20 n, 17 e. C. 47 p+, 60 n, 47 e- 16 O 8 ______ 37 Cl 17 ______ 107 Ag 47 ______ Lecture. PLUS Timberlake 23

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 2) 34 X 14 Lecture. PLUS Timberlake 3) 36 X 14 24

Masses of Atoms l A scale designed for atoms gives their small atomic masses in atomic mass units (amu) l An atom of 12 C was assigned an exact mass of 12. 00 amu l Relative masses of all other atoms was determined by comparing each to the mass of 12 C l An atom twice as heavy has a mass of 24. 00 amu. An atom half as heavy is 6. 00 amu. 25 Lecture. PLUS Timberlake

Atomic Mass Na 22. 99 l Listed on the periodic table l Gives the mass of “average” atom of each element compared to 12 C l Average atom based on all the isotopes and their percent abundance (% abundance) l Atomic mass is not a whole number Lecture. PLUS Timberlake 26

Learning Check AT 6 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 _____ 137. 3 amu _____ 55. 8 amu _____ D. barium E. iron Lecture. PLUS Timberlake 27

Calculating Atomic Mass l Percent abundance of isotopes l Mass of each isotope of that element l Weighted average = mass isotope 1(%) + mass isotope 2(%) + … 100 Lecture. PLUS Timberlake 28

Atomic Mass of Magnesium Isotopes 24 Mg = Mass of Isotope 24. 0 amu Abundance 78. 70% 25 Mg = 25. 0 amu 10. 13% 26 Mg = 26. 0 amu 11. 17% Atomic mass (average mass) Mg = 24. 3 amu Mg 24. 3 Lecture. PLUS Timberlake 29

Learning Check AT 7 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? Lecture. PLUS Timberlake 30

Solution AT 7 Ga-69 (%/100) 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 Lecture. PLUS Timberlake 31

Finding An Isotopic Mass A sample of boron consists of 10 B (mass 10. 0 amu) and 11 B (mass 11. 0 amu). If the average atomic mass of B is 10. 8 amu, what is the percent abundance of each boron isotope? Lecture. PLUS Timberlake 32

Assign X and Y values: X = % 10 B Y = % 11 B Determine Y in terms of X X + Y = 100 - X Solve for X: X (10. 0) + (100 - X )(11. 0) 100 = 10. 8 Multiply through by 100 10. 0 X + 1100 - 11. 0 X = 1080 Lecture. PLUS Timberlake 33

Collect X terms 10. 0 X - 11. 0 X = 1080 - 1100 - 1. 0 X = -20 - 1. 0 = Y = 100 - X % 11 B = 100 - 20% = 20 % 10 B 80% 11 B Lecture. PLUS Timberlake 34

Learning Check AT 8 Copper has two isotopes 63 Cu (62. 9 amu) and 65 Cu (64. 9 amu). What is the percent abundance of each isotope? (Hint: Check periodic table for atomic mass) Lecture. PLUS Timberlake 35

Solution AT 8 2) 70% Solution 62. 9 X + 6490 = 64. 9 X = 6350 -2. 0 X = -140 X = 70% Lecture. PLUS Timberlake 36