The Atomic Number and Mass Number Isotopes R
The Atomic Number and Mass Number Isotopes R. Krum GHS 1
Atomic Theory l Atoms are building blocks of elements l Similar atoms in each element l Different from atoms of other elements l Two or more different atoms bond in simple ratios to form compounds 2
Subatomic Particles Particle Symbol Charge Relative Mass 0 Electron e- 1 - Proton p+ + 1 Neutron n 0 1 3
Location of Subatomic Particles 10 -13 cm electrons protons nucleus neutrons 10 -8 cm 4
Atomic Number Counts the number of protons in an atom 5
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 6
Periodic Table 1 2 3 4 5 6 7 8 11 Na 7
Atomic Number on the Periodic Table Atomic Number Symbol 11 Na 8
All atoms of an element have the same number of protons 11 protons Sodium 11 Na 9
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 3) 6 protons C. Barium 1) 137 protons 2) 81 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 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 12
Mass Number Counts the number of protons and neutrons in an atom 13
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 14
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- 30 Zn 15
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 chlorine - 37 16
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 6 13 C 6 14 C 6 #P _______ #N _______ #E _______ 17
Solution AT 2 12 C 6 13 C 14 C 6 6 #P __6___ ___6___ #N __6___ _ _7___ ___8___ #E __6___ ___6___ 18
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 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 20
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- ___________ 21
Solution AT 4 16 O 8 A. 8 p+, 8 n, 8 e- 37 Cl B. 17 p+, 20 n, 17 e- 17 C. 47 p+, 60 n, 47 e- 107 Ag 47 22
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 C. The element is 1) Si 2) Ca 3) 34 3) Se D. Another isotope of this element is 1) 34 X 16 14 2) 34 X 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) 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
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 abundance % l Atomic mass is not a whole number 26
Learning Check AT 6 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 _____ 27
Solution 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_ D. barium _137. 3 amu_ E. iron _55. 8 amu__ 28
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 29
Atomic Mass of Magnesium Isotopes 24 Mg = Mass of Isotope Abundance 24. 0 amu 78. 70% 25 Mg = 25. 0 amu 10. 13% = 26. 0 amu 11. 17% 26 Mg Atomic mass (average mass) Mg = 24. 3 amu Mg 24. 3 30
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? 31
Solution AT 7 Ga-69 68. 9 amu x 60. 2 = 41. 5 amu for 69 Ga 100 Ga-71 (%/100) 70. 9 amu x 39. 8 100 = 28. 2 amu for Atomic mass Ga = 69. 7 amu 71 Ga 32
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 % abundance of each boron isotope? 33
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) = 10. 8 100 Multiply through by 100 10. 0 X + 1100 - 11. 0 X = 1080 34
Collect X terms 10. 0 X - 11. 0 X = 1080 - 1100 - 1. 0 X = -20 - 1. 0 = 20 % 10 B Y = 100 - X % 11 B = 100 - 20% = 80% 11 B 35
Learning Check AT 8 Copper has two isotopes 63 Cu (62. 9 amu) and 65 Cu (64. 9 amu). What is the % abundance of each isotope? (Hint: Check periodic table for atomic mass) 1) 30% 2) 70% 3) 100% 36
Solution AT 8 2) 70% Solution 62. 9 X + 6490 = 64. 9 X = 6350 -2. 0 X = -140 X = 70% 37
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