Nuclear Chemistry Chapter 21A West Valley High School General Chemistry Mr. Mata

Standard 11d Students know the three most common forms of radioactive decay are alpha, beta, and gamma particles.

Essential Question: What are the three main types of radiation and how do they differ from each other?

Nuclear Reactions Reactions that occur in the NUCLEUS. Differ from chemical reactions. Cannot be slowed down, sped up, or turned off.

Chemical Reactions vs. Nuclear Reactions Atoms gain stability by attaining stable electron configurations (loss or gain of e-’s). Nuclear Reactions: Unstable isotopes (radioisotopes) gain stability by making changes within their nuclei. Not affected by pressure, temp., or catalysts. Radioisotopes have unstable nuclei.

Radioactivity Stability of the nucleus: Ratio of neutrons to protons. Too many or few neutrons relative to the # of protons = unstable nucleus. Out of 1500 known nuclei, 264 are stable.

Radioactive Decay The process in which an unstable nucleus loses energy by emitting radiation. Spontaneous process. Does not need any input of energy. Unstable radioisotopes are eventually transformed into stable (nonradioactive) isotopes of a different element.

Ernest Rutherford Used U and Th in a magnetic field. Alpha and beta particles were deflected by a magnetic field. Gamma rays moved through the field without being affected.

3 Types of Radiation ALPHA () radiation—could be stopped by a sheet of paper +2 charge --helium atom 42He BETA () radiation—could be stopped by a sheet of aluminum -1 charge --high-speed electron

Types of Radiation (cont.) GAMMA () radiation—could be stopped by lead No charge --no mass

Penetrating Ability of Types of Radiation Insert figures 18.4, 18.5

Tissue Damage Tissue damage measured in mrems. Alpha particles have little penetrating power and are not harmful unless ingested. Beta particles are more damaging because they can penetrate further. Gamma rays are most penetrating and can cause the most damage.

Radiation Detectors Geiger Counters Film badges Detect ionization caused by radiation. Recorded by electronic devices (“clicks”). Film badges react to radiation as film exposure to light. greater radiation = greater film exposure.

Background Radiation Cosmic rays (from outer space). Naturally sources: air, water, soil, rocks. 40K, 232Th, 222Rn, 238U Artificial sources: X-rays, nuclear medicine. Fallout from nuclear accidents and testing. Average dose- 100 mrem/year.

Uses of Radioactivity Non-medical tracers determine pathways & material flow. activation analysis (cause certain elements to become radioactive). preserve food. C-14 dating (used to date fossils & artifacts).

Medical Uses of Radiation Medical applications: Thyroid gland uptake of 131I to diagnose thyroid disease. Measuring blood flow. PET (Positron Emission Topography body scan). Treatment of tumors (chemotherapy).

Half-Life Half-life (t1/2): the time required for one-half of the atoms of a radioisotope to decay into new product(s).

Example: Half-life Assume there are 2.00 g of N-13. How many grams of N-13 will exist after 3 half-lives? # of half-lives Mass of N-13 0 2.00 g 1 1.00 g 2 0.50 g 3 0.25 g

Transmutation Reactions Transmutation: conversion of atom of one element to atom of another element. Some occur naturally by decay (, ). Some artificially made in labs. High-energy particles bombard nucleus of an atom.

Transuranium Elements Elements in the periodic table with atomic numbers above 92. None occur in nature and all are radioactive. Synthesized in nuclear reactors and nuclear accelerators.