Radioisotopes Introduction to Nuclear Chemistry

OBJECTIVES: Explain what causes an isotope to become unstable. Compare and contrast chemical vs. nuclear reactions. Explain how an unstable nucleus releases energy. Identify the three types of nuclear radiation and their properties.

ISOTOPES REVIEW Isotopes: Different atoms of the same element that have the same number of protons but different number of neutrons. Examples: Carbon-12, Carbon-13

Two Categories of Isotopes Unstable – isotopes that continuously and spontaneously break down/decay in other lower atomic weight isotopes Stable – isotopes that do not naturally decay but can exist in natural materials in differing proportions

What causes isotopes to become unstable? An unhealthy ratio of neutrons to protons. The most stable ratio of neutrons to protons is 1:1. Ex: Lithium has 6 isotopes; Li-6, Li-7, Li-8, Li-9, Li-10, and Li-11. Only Li-6 and Li-7 are stable: Li-6 has 3 protons and 3 neutrons; 3 neutrons = 1:1 ratio Li-9 = 6 neutrons = 2:1 ratio 3 protons stable 3 protons unstable The ratio of neutrons to protons is higher than 1:1; so they are unstable.

Phet Colorado Simulation Isotopes and Atomic Mass www. phet. colorado Phet Colorado Simulation Isotopes and Atomic Mass www. phet.colorado.edu Go to the following website: www.phet.colorado.edu (Use firefox if Safari doesn’t work) Type in Isotopes and Atomic Masses in the search bar at the top of the page. When the simulation appears, click on “Isotopes” Observe the isotopes of hydrogen and lithium, and their stable and unstable isotopes. Look at Lithium; which isotopes are unstable? Why?

Radioactivity Was first observed by Marie and Pierre Curie (1900s) using uranium (U) atoms. Radioactivity: The process by which substances spontaneously emit rays and particles (radiation).

Radioactivity differs from chemical reactions in a number of ways: In chemical reactions, atoms attain a stable electron configuration by losing/sharing electrons. In nuclear reactions, the nucleus of an unstable isotope gains stability by undergoing changes. Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure, or the presence of catalysts. Nuclear reactions of an isotope cannot be sped up, slowed down, or turned off

Radioactivity Unstable radioactive isotopes (radioisotopes) are transformed into stable (nonradioactive) isotopes of a different element. Radioactive decay: is the process by which an unstable nucleus releases energy by emitting radiation in the form of alpha, beta, or gamma decay.

Types of Radiation 2. Beta Radiation 3. Gamma Radiation 1. Alpha Radiation 2. Beta Radiation 3. Gamma Radiation

Alpha (α) Radiation Recall, Rutherford used alpha particles to discover the nucleus in his Gold Foil Experiment Usually written as α or 42He. Due to its large mass and charge, alpha particles do not travel very far. They cannot penetrate very well – a sheet of paper or the surface of your skin stops them. However, they are toxic when ingested.

Alpha (α) Radiation U Th + He Example: Alpha decay of Uranium-238 238 92 Radioactive decay Th 234 90 + He 4 2 U-283 is used in geological dating (uncovering the age of rocks)

Alpha Decay

Beta (β) Radiation Results from the breaking apart of a neutron into a proton and an electron (beta particle). Usually written as: 0-1e or β Has much less mass than an alpha particle and can therefore penetrate more easily. Can pass through paper, but is stopped by foil or wood.

Beta (β) Radiation C N + e Example: Beta decay of Carbon-14 14 6 Radioactive decay N 14 7 + e ----1- C-14 is used in determining the age of organic matter

Beta Decay Thorium Protactinium

Gamma (γ) Radiation A high energy photon emitted by a radioisotope. Usually written as: 00γ or γ Often emitted with alpha or beta particles during radioactive decay. Gamma rays are electromagnetic waves Has no mass or charge. Extremely penetrating and can be very dangerous. Easily passes through paper, wood, and the human body. Penetration can be stopped, although not completely, by several centimeters of lead.

Gamma (γ) Radiation γ Th Rn He + + Example: Gamma/alpha emission from Thorium-230 γ Th 230 90 Radioactive decay Rn 226 88 He 4 2 + +

CLASSWORK / HOMEWORK Type an ½ page essay listing and explaining the benefits and dangers of radioisotopes. Due tomorrow