Chemistry Chapter 3 and 24Atoms, Ions, Isotopes and Nuclear Chemistry These notes will enable the student to understand concepts related to the nucleus of the atom and basic nuclear chemistry
Chapter 24 Nuclear ChemistrySection 1: Radioisotopes • A. General Information • 1. Carbon atoms can be stable or unstable • 2. Many other atoms have the same characteristics of stability • These combination of unstable and stable forms of the same atom are called Isotopes
I. Radioisotopes • B. Radioisotope • 1. All nuclear decay is accompanied by radiation emission • a. called radioactivity • b. discovered in 1896 by H. Becquerel by placing photo film in a drawer with uranium ore • c. film showed signs of exposure • d. radiation passed through a piece of black paper and produced an image on the film
I. Radioisotopes • B. Radioisotope • 2. Decay of unstable isotopes is spontaneous • a. all elements have 1 or more isotopes • b. the unstable isotopes decay to produce other elements • c. many elements have at least 1 radioactive isotope or radioisotope that occurs naturally • Fluorine is an example of one that does not have 1 radioisotope (F-19 is stable)
I. Radioisotopes • C. Half-life • 1. Definition: The half-life of a radioactive isotope is the same time it takes for ½ of a sample of isotope to decay • a. follow an example: Rb – 2 isotopes, 85Rb and 87Rb 85Rb is 72.15% of total amount (in nature) 87Rb is 27.85% of total amount (in nature) 85Rb is stable 87Rb is radioactive (gives off Beta decay particles)
I. Radioisotopes • C. Half-life (cont) • 1. Definition (cont) 87Rb 87Sr + 0e 3738-1 Remember, with Beta decay, a neutron is converted to 1 proton and 1 electron. So they lose the electron, but the proton remains (+1 proton = new element). In some cases, the electron stays and the proton is released
I. Radioisotopes • C. Half-life (cont) • 1. Definition (cont) • b. second example: Tin-124 (124Sn) 124Sn 124Sb + 0e 5051-1 • c. The half-life of 87Rb is 6x1010 years (60 billion) In 60 Billion years ½ of the concentration of 87Rb in the sample would be converted to 87Sr So, if we start with 1.000g, in 60 billion years we would have ______g. In another 60 billion years we would have _____g.
I. Radioisotopes • C. Half-life (cont) • 1. Definition (cont) • d. the slower the decay, the slower the radioactive production • 2. Examples of Radioactive isotopes Forms Isotopes Half-life (yrs) Decay Type Uranium-238 4.5x109 alpha Natural Uranium-235 7.1x108 alpha Thorium-232 1.4x1010 alpha Potassium-40 1.3x109 beta Carbon-14 5730 alpha
I. Radioisotopes • C. Half-life (cont) • 2. Examples of Radioactive isotopes Forms Isotopes Half-life (yrs) Decay Type Plutonium-239 24,000 alpha Unnatural Cesium-137 30 beta Strontium-90 28.8 beta Iodine-131 .022 beta
I. Radioisotopes • D. Nuclear Bombardment Reactions • 1. General Information • a. Radioactive isotopes go through spontaneous nuclear reactions to become stable • b. It is possible to make a stable isotope unstable • Nuclear Bombardment
I. Radioisotopes • D. Nuclear Bombardment Reactions • 1. General Information • a. A nuclear bombardment reaction is when an atom is bombarded with a stream of particles (ex. Alpha) • When particles hit, they combine to become a new nucleus • Discovered by Ernest Rutherford • Discovered when an alpha particle strikes a 14Nitrogen nucleus, an Oxygen-12 and Hydrogen-1 are produced. • 24O + 714N 817O + 11H • Mass numbers and atomic numbers are balanced
I. Radioisotopes • D. Nuclear Bombardment Reactions • 1. General Information • b. Using alpha particles are difficult because both nuclei have (+) positive charges. • Alpha particles must move extremely fast. • Sometimes called atom smashers (particle accelerators) • Several types of particle accelerators
I. Radioactive Isotopes • D. Nuclear Bombardment Reactions • 1. General Information • c. Using neutrons (particles) can create artificial radioactive isotopes. • example.: Molybdenum -98 to technecium-99 • 01n + 4298Mo 4399TC + -10e • Technecium-99 is used to detect brain tumors • Neutron particles produces an electron (10e), it is not a B particle because a neutron is not changed into one proton and one electron.
Radioactive Isotopes • D. Nuclear Bombardment Reactions • 1. General Information Sample problem • “The neutron bombardment of calcium-40 produces potassium-40 and “possibly” another particle as a byproduct.” Write the nuclear equation for this reaction. • If it is potassium-40 and a secondary particle, the particle