Isotopes Rev. 022609 Pisgah High School M. Jones.

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Isotopes Rev. 022609 Pisgah High School M. Jones

Isotopes … …have the same number of protons and electrons but different numbers of neutrons. Therefore, isotopes of the same element have different masses.

Isotopes … Atomic number - the number of protons in the nucleus of an atom Mass number - the number of protons added to the number of neutrons …have different mass numbers but the same atomic number.

Symbols for Isotopes E A Z Symbol of Element Mass number Atomic number A is the symbol for mass number Z is the symbol for atomic number

Symbols for Isotopes U 235 92 Symbol of Element Mass number Atomic number

Symbols for Isotopes U 235 92 Mass number Symbol of Element Atomic number

Symbols for Isotopes U -235 Symbol of Element Mass number How do you know the atomic number? Find U in the periodic table. Z = 92

Determining the Atomic Number and Mass Number The atomic number is the number of protons. The atomic number is the number of protons. The mass number is the sum of the protons + neutrons. The mass number is the sum of the protons + neutrons. Consider an atom of aluminum with 13 protons and 15 neutrons. What is Z and A?

Determining the Atomic Number and Mass Number A = #p + + #n 0 13 + 15 = 28 Answer: Atomic number: Z = 13 Mass number: A = 28

Finding the number of Protons, Neutrons, and Electrons The atomic number is the number of protons in the nucleus. The number of electrons in a neutral atom equals the number of protons.

Finding the number of Protons, Neutrons, and Electrons # of neutrons = A - Z The number of neutrons is the difference between the mass number and the atomic number.

Finding the number of Protons, Neutrons, and Electrons Look at the Periodic Table and find the element by using the symbol U-235 A = 235 protons + neutrons = 235 Z = 92 protons = 92 electrons = 92

Finding the number of Protons, Neutrons, and Electrons U-235 Z = 92 protons = 92 electrons = 92 A = 235 protons + neutrons = 235 235 prot.& neut. - 92 protons 143 neutrons

Finding the number of Protons, Neutrons, and Electrons Q. Find the number of neutrons in the Ba-137 isotope. A. In the Ba-137 isotope … … Z = 56 and A = 137 137 – 56 = 81 neutrons

Finding the number of Protons, Neutrons, and Electrons Fill in the following table.

Finding the number of Protons, Neutrons, and Electrons ElementSymbolZA#p#n#e Zinc66 In68 8538 82210 Rn136 3547

ElementSymbolZA#p#n#e ZincZn3066303630 In68 8538 82210 Rn136 3547

ElementSymbolZA#p#n#e ZincZn3066303630 IndiumIn49117496849 8538 82210 Rn136 3547

ElementSymbolZA#p#n#e ZincZn3066303630 IndiumIn49117496849 StrontiumSr3885384738 82210 Rn136 3547

ElementSymbolZA#p#n#e ZincZn3066303630 IndiumIn49117496849 StrontiumSr3885384738 LeadPb822108212882 Rn136 3547

How are isotopes of the same element alike and different? Alike: 1. Number of protons and electrons 2. Atomic number 3. Chemical properties Different: 1. Number of neutrons 2. Mass Number 3. Atomic weight of the isotopes

Which of the following is the same for the three isotopes of magnesium? 1.The atomic number of 12 2.The number of protons and electrons 3.The number of neutrons 4.The atomic weight of 24.986 AMU 5.The reaction with hydrochloric acid 6.The speed of gaseous Mg atoms

Which of the following is the same for the three isotopes of magnesium? 1.The atomic number of 12 All three isotopes of magnesium have the same atomic number. Same

Which of the following is the same for the three isotopes of magnesium? 2. The number of protons and electrons All isotopes of the same element have the same number of protons in the nucleus, and electrons outside the nucleus. Same

Which of the following is the same for the three isotopes of magnesium? 3. The number of neutrons The number of neutrons varies with the isotope. Different isotopes have different numbers of neutrons. Not the same

Which of the following is the same for the three isotopes of magnesium? 4. Atomic weight of 24.986 AMU Mg-24  23.985 AMU Mg-25  24.986 AMU Mg-26  25.983 AMU Not the same

Which of the following is the same for the three isotopes of magnesium? 5. The reaction with HCl All isotopes of the same element react the same chemically. Same The number and arrangement of electrons is the same for each isotope.

Which of the following is the same for the three isotopes of magnesium? 6. The speed of gaseous Mg atoms The speeds of atoms depend on mass. Heavier atoms move more slowly, and lighter atoms move faster. Not the same

How did knowing that the speeds of gaseous isotopes are different, allow the United States to win World War II?

Who were the two guys responsible for winning World War II? Fat Man, and … Little Boy Atomic bombs dropped on Hiroshima and Nagasaki

Manhattan Project Oak Ridge, TN Gaseous Diffusion To sustain a nuclear chain reaction, uranium must be at least 4% U-235. Most naturally occurring uranium is U-238 Less than 1% of naturally occurring uranium is U-235

To make either bomb-grade uranium, or fuel for a nuclear reactor you need enriched uranium. Enriched uranium has a higher percentage of U-235. 12% for a reactor, 90% for a bomb.

The gaseous diffusion plant at Oak Ridge was used to make enriched uranium. The uranium oxide is reacted with fluorine to make UF 6 which is a gas. The UF 6 is introduced into a container with a porous barrier.

The molecules of UF 6 containing U- 235 diffuse through the porous barrier slightly faster. Produces a slightly higher percentage of U-235 in the UF 6. Produces a slightly higher percentage of U-235 in the UF 6. Then the process is repeated many times.

The K-25 building at Oak Ridge

Atomic Weights

Calculating Average Atomic Weight Atomic mass (atomic weight) is the weighted average of the masses of all the isotopes of the element.

Calculating Average Atomic Weight A weighted average puts more weight or importance on one value that another. Example: Compute the average age of everyone in this room.

Calculating Average Atomic Weight Suppose there were two isotopes of the element Q. Q-30 95% Q-32 5% Determine the average atomic mass.

Calculating Average Atomic Weight Is the average atomic weight 31? ( 30 + 32 ) / 2 = 31 Assume 100 atoms of Q: 95 x 30 amu = 2850 5 x 32 amu = 160 5 x 32 amu = 160 / 100 = 30.1 amu 3010 Much closer to 30

Calculating Average Atomic Weight of each naturally occurring isotope. of each naturally occurring isotope. You can compute the atomic weight by knowing … … the mass (M) and … the relative abundance (RA)

Calculating Average Atomic Weight The mass is the actual mass of the isotope in amu. The relative abundance is the percentage of that isotope divided by 100.

Calculating Average Atomic Weight Example: Suppose that 48.6% of the atoms of zinc in the world were Zn-64. Then the relative abundance of zinc-64 would be 0.486.

Calculating Average Atomic Weight (M 3 * RA 3 ) … (M 2 * RA 2 ) + (M 1 * RA 1 ) + Average atomic weight = Mass of each isotope times its relative abundance

Calculating Average Atomic Weight Calculate the average atomic weight for Cu-63 and Cu-65. Actual mass of isotope in AMU Percent abundance Cu-6362.929869.09% Cu-6564.927830.91%

Calculating Average Atomic Weight AW = 63.55 AMU AW = (62.9298 *.6909) + AW = (M 1 * RA 1 ) + (M 2 *RA 2 ) Calculate the average atomic weight for Cu-63 and Cu-65. (64.9278 *.3091)

Calculate the Average Atomic Weight of Chlorine Actual mass of isotope in AMU Percent abundance Cl-3534.96975.77% Cl-3736.96624.23% Stop Do the calculations, then continue.

Calculate the Average Atomic Weight of Chlorine Actual mass of isotope in AMU Percent abundance Cl-3534.96975.77% Cl-3736.96624.23% AW = (34.969 * 0.7577) + (36.966 * 0.2423) AW = 35.45 AMU

Which isotope of Boron is more abundant? B-10 ??? % 10.01 amu B-11 ??? % 11.01 amu Give a qualitative answer. A qualitative answer does not require calculations, just thought.

Which isotope of Boron is more abundant? B-10 ??? % 10.01 amu B-11 ??? % 11.01 amu B-11 is more abundant because 11.01 is closer to 10.81, the actual average mass of Boron.

Which isotope of Boron is more abundant? B-10 ??? % 10.01 amu B-11 ??? % 11.01 amu Now stop and compute the actual percentages.

Which isotope of Boron is more abundant? B-10 ??? % 10.01 amu B-11 ??? % 11.01 amu Did you get 20.00% B-10 and 80.00% B-11?

Some isotope trivia…

Only one element has unique names for its isotopes … Deuterium and tritium are used in nuclear reactors and fusion research.

Man-made Isotopes Man made isotopes are made by bombarding atoms with streams of protons or neutrons. Man made isotopes are made by bombarding atoms with streams of protons or neutrons. Cobalt-59 occurs naturally. Cobalt-60 occurs in reactors after neutron exposure. Cobalt-59 occurs naturally. Cobalt-60 occurs in reactors after neutron exposure.

Uses for Isotopes Various radioisotopes are used to kill cancer cells. (Co-60, Bi-212) Various radioisotopes are used to kill cancer cells. (Co-60, Bi-212) Radioisotopes are used in imaging living and nonliving systems. Tc-99 Radioisotopes are used in imaging living and nonliving systems. Tc-99 Radioisotopes are used as tracers in chemical reactions. Radioisotopes are used as tracers in chemical reactions.

Isotopes