CHEM 108 The Nucleus Isotopes / Atomic Mass and The Periodic Table __________ Isotopes / Atomic Mass and The Periodic Table

Nuclear Decay / Radioactivity http://chemconnections.org/general/movies/Radioactivity.MOV Unstable nuclei are radioactive. They “decay”, i.e. they emit particles, which lead to different elements and isotopes that can be detected and accurately measured. 10 Decay Modes: Gamma emission, electron conversion β- decay β+ decay Electron Capture (EC) β-delayed particle emission Double β decay Proton decay Alpha decay Cluster decay Spontaneous Fission (SF)

http://chemconnections. org/general/movies/radioactivityofeverydayob http://chemconnections.org/general/movies/radioactivityofeverydayob.mov http://www.pbs.org/video/2209769748/

Radioactive Decay Uranium alpha () decay Radium Thorium Fiesta Plate Radium alpha () decay Watch Face Lantern mantle-Thorium Fiesta Plate-Uranium Polonium- Cobalt Lead Shield Thorium alpha () decay Lantern Mantle

Nuclear Particles emitted from unstable nucleii Emitted Nuclear Particles: Mass Charge Symbol alpha particle 4 amu +2 beta particle very small -1 gamma very very small 0 10 Decay Modes: Gamma emission, electron conversion β- decay β+ decay Electron Capture (EC) β-delayed particle emission Double β decay Proton decay Alpha decay Cluster decay Spontaneous Fission (SF) positron very small +1

Nuclides http://www.nndc.bnl.gov/chart/ 10 Decay Modes: Gamma emission, electron conversion β- decay β+ decay Electron Capture (EC) β-delayed particle emission Double β decay Proton decay Alpha decay Cluster decay Spontaneous Fission (SF)

Number of Stable Isotopes (Nuclides) Elements 48 through 54 Atomic Number of Element Number (Z) Stable Nuclides Cd 48 8 In 49 2 Sn 50 10 Sb 51 2 Te 52 8 I 53 1 (37) Xe 54 9 have a higher average binding energy per nucleon than one would expect based upon predictions such as the semi-empirical mass formula and are hence more stable against nuclear decay Magic numbers are 2, 8, 20, 28, 50, or 82 protons or neutrons. Even numbers of protons and neutrons are more stable than odd.

Distribution of Stable Nuclides Protons Neutrons Stable Nuclides % Even Even 157 58.8 Even Odd 53 19.9 Odd Even 50 18.7 Odd Odd 7 2.6 Total = 267 100.0%

QUESTION alpha particle +2 amu beta particle -1 amu Mass emitted In alpha decay, the nucleus looses the equivalent of 2 protons and the element’s atomic number (a.n.) is decreased by 2, producing another element whose (a.n.) is 2 less. What is the change in atomic number of a nucleus that results from beta decay? +1 +2 –1 –2 Emitted Particles: Mass emitted alpha particle +2 amu beta particle -1 amu Answer: A

Nuclear Penetrating Power alpha particle: low beta particle: moderate gamma: high X-rays: high Water

Nuclear Penetrating Power Human Absorbtion Radiation effects are cumulative (Madame Curie: 1867-1934) rad = radiation absorbed dose ( 0.01 J/kg) rem= radiation equivalent for man (1 rem = 1 rad x Q; Q=1 for β, γ, X-rays; Q= 3-10 for neutrons; Q=10 for p+; Q= 20 for -particles) Background radiation = 0.13 rem Annual exposure limit is set at 0.17 rem above background Dosimeters measure radiation absorbed aplastic anemia ""Nothing in life is to be feared; it is only to be understood." and X-rays Marie Skłodowska Curie (1867-1934: aplastic anemia), was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. 1903 Nobel Prize in Physics with her husband Pierre Curie and with physicist Henri Becquerel-radioactivity for isolating radium, the 1911 Nobel Prize in Chemistry- Polonium First woman professor University of Paris 1906 1911 Nobel Prize in Chemistry for discovery of the elements radium and polonium, by the isolation of radium and the study of the nature and compounds of this remarkable element. During World War I, she developed mobile radiography units to provide X-ray services to field hospitals treating more than 1 million wounded.

Which type of radioactive emission is the most penetrating? QUESTION Which type of radioactive emission is the most penetrating? Emitted Particles: Mass Charge alpha particle 4 amu +2 beta particle very small -1 gamma very very small 0 Alpha Beta Gamma Delta Zeta Answer: C

Mrs. Element #111’s hand and ring (What’s her name?) Medical X-Rays Hand mit Ringen (Hand with Rings): print of Wilhelm Röntgen's first "medical" X-ray, of his wife's hand, taken on 22 December 1895 and presented to Ludwig Zehnder of the Physik Institut, University of Freiburg, on 1 January 1896 Marie Skłodowska Curie (/ˈkjʊri, kjʊˈriː/;[2] French: [kyʁi]; Polish: [kʲiˈri]; 7 November 1867 – 4 July 1934), born Maria Salomea Skłodowska [ˈmarja salɔˈmɛa skwɔˈdɔfska], was a Polish and naturalized-French physicist and chemist who conducted pioneering research on radioactivity. She was the first woman to win a Nobel Prize, the first person and only woman to win twice, the only person to win twice in multiple sciences, and was part of the Curie family legacy of five Nobel Prizes. She was also the first woman to become a professor at the University of Paris, and in 1995 became the first woman to be entombed on her own merits in the Panthéon in Paris. She was born in Warsaw, in what was then the Kingdom of Poland, part of the Russian Empire. She studied at Warsaw's clandestine Floating University and began her practical scientific training in Warsaw. In 1891, aged 24, she followed her older sister Bronisława to study in Paris, where she earned her higher degrees and conducted her subsequent scientific work. She shared the 1903 Nobel Prize in Physics with her husband Pierre Curie and with physicist Henri Becquerel. She won the 1911 Nobel Prize in Chemistry. Her achievements included the development of the theory of radioactivity (a term that she coined[3][4][5]), techniques for isolating radioactive isotopes, and the discovery of two elements, polonium and radium. Under her direction, the world's first studies were conducted into the treatment of neoplasms, using radioactive isotopes. She founded the Curie Institutes in Paris and in Warsaw, which remain major centres of medical research today. During World War I, she established the first military field radiological centres. First Medical X-Ray (1895) Mrs. Element #111’s hand and ring (What’s her name?) Mrs. Wilhelm Röntgen

Where does most of our yearly exposure to radiation come from? QUESTION Where does most of our yearly exposure to radiation come from? Nuclear power plants Smoke detectors Medical X-rays Naturally occurring sources Human-made sources

CHEMISTRY of the Atom Isotopes vary in their relative natural abundance. Periodic Table’s atomic mass is a weighted average of all isotopic masses The mass of sodium, Na, element #11 is listed as 22.99 amu. Which isotope is naturally present in the larger amount: the isotope with 12 neutrons or with 13 neutrons? (There is a small percentage of the isotope with 11 neutrons.)

QUESTION Two stable isotopes of an element have isotopic masses of 10.0129 amu and 11.0093 amu. The atomic mass is 10.81. Which isotope is more abundant? A) There is insufficient information to answer the question. B) There are equal amounts of each isotope. C) The isotope with a mass of 10.0129 amu is more abundant. D) The isotope with a mass of 11.0093 amu is more abundant. Correct Answer: D Question Number: 10

CHEMISTRY of Atoms Unstable Isotopes and Time Carbon’s three Nuclides: Stable Unstable

CHEMISTRY of Atoms Unstable Isotopes and Time https://en.wikipedia.org/wiki/Radiocarbon_dating Atomic Number = 6 (atom’s identity) Carbon-14 Atomic Mass = 14 (isotope 14) 6 protons; 8 neutrons = 14 – 6 14C : Unstable, beta decay Half life = 5,730±40 years Accelerator mass spectrometer at Lawrence Livermore National Laboratory "The 1 MV accelerator mass spectrometer was (see photo) developed partially under the Resource funding. 14C and tritium analyses of biomedical samples submitted by Resource users are conducted using this 1 MV system. The AMS spectrometer consists of a cesium sputter source, low-energy injection beam line, the high voltage collision cell (accelerator), a high-energy mass spectrometer and a particle detector for energy measurements (proceeding clockwise from lower left in the photograph)." Accelerator Mass Spectrometer Lawrence Livermore National Laboratory

Radioactive Decay of 14C Over Time https://www.nobelprize.org/nobel_prizes/chemistry/laureates/1960/ The Nobel Prize in Chemistry 1960 was awarded to Willard F. Libby "for his method to use carbon-14 for age determination in archaeology, geology, geophysics, and other branches of science".

QUESTION Which of the following is the best definition of the half-life of a radioactive isotope? The time it takes for 50% of the parent nuclide atoms to decay to the daughter nuclide atoms The time it takes for a 50% reduction in radioactivity The lifetime of a radioactive sample The time it takes for 25% of the parent nuclide atoms to decay to the daughter nuclide atoms The time it takes for 100% of the parent nuclide atoms to decay to the daughter nuclide atoms Answer: A

QUESTION Based solely on the following half-lives, which radioactive atom in the list is the most radioactive, that is, decays the fastest? 14C Carbon-14 (5730 yrs) 226Ra Radium-226 (1620 yrs) 238U Uranium-238 (4.5 million yrs) 214Po Polonium-214 (1.6 ms) 32P Phosphorus-32 (14 days) Answer: D

Radiocarbon Dating for Determining the Age of Artefacts Ground Sloth Dung (Off scale) 

QUESTION An artefact of ground sloth dung was originally thought to have been recently deposited, but on analysis was found to be much older. Based on radio carbon dating, the sample was at the test’s limits (~7 half lives old). How many years old was this sample thought to be? (C-14 half-life is 5730 years.) Answer: D 5.73 × 103 yr 1.72 × 104 yr 2.29 × 104 yr 2.87 × 104 yr 4.01 × 104 yr

K K 39 19 39 Writing Atomic Symbols (Not Written the Same as in the Periodic Table) 39 K Mass number   Element Symbol 19 Atomic number  39 K Also written as 

CHEMISTRY of the Atom Atomic Number = 6 (atom’s identity) Carbon Atomic Mass = 13 (isotope 13) 6 protons; # neutrons = 13 - 6 neutral atom has 6 electrons

CHEMISTRY of the Atom Atomic Mass of Carbon: What is the “weighted” atomic mass? 12.00000 x 98.98/100 + 13.00335 x 1.011 = 11.8776 + 0.13146 = 12.0090 12.01

QUESTION