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Nuclear Chemistry

Nuclear Chemistry. Describe radioactivity through a balanced nuclear equation and through an analysis of the half life concept. Chemical Reactions vs Nuclear Reactions Review of Isotopes Definition of Radioactivity and emissions Discussion of the three most important types of emissions

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Nuclear Chemistry

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  1. Nuclear Chemistry

  2. Describe radioactivity through a balanced nuclear equation and through an analysis of the half life concept.

  3. Chemical Reactions vs Nuclear Reactions • Review of Isotopes • Definition of Radioactivity and emissions • Discussion of the three most important types of emissions • What do we mean by half-life? • Where is Radioactivity encountered? • Is Radioactivity dangerous?

  4. What is a Chemical Reaction? • Chemical reactions involve changing one substance into another substance by rearranging atoms. • However, during a chemical reaction, atoms of one element cannot change into atoms of another element. • The reason this change cannot occur is that chemical reactions only involve an atom's electrons – the nucleus remains unchanged. • Recall that an atom's identity is based on its number of protons. • Since protons are in the nucleus and chemical reactions do not involve the nucleus, the atom remains unchanged. • ed.

  5. What is a Nuclear Reaction? • There are some reactions that do involve changes in the nucleus. • These are called nuclear reactions. • In nuclear reactions, one atom of an element changes into an atom of a different element.

  6. Isotopes • Fill in the table below as a review. • You will need your periodic table for this! • Remember the atomic number (or # of protons) determines the element. • Example:If an atom has four protons and seven neutrons, it is beryllium. The same is true of an atom containing four protons and six neutrons...the atom is still beryllium.

  7. Early Pioneers in Radioactivity Roentgen: Discovered of X-rays 1895 Becquerel: Discovered of Radioactivity 1896 Roentgen: Discoverer of X-rays 1895 Becquerel: Discoverer of Radioactivity 1896 Rutherford: Discovered Alpha and Beta rays 1897 The Curies: Discovered Radium and Polonium 1900-1908

  8. What do we mean by Radioactivity? • Radioactivity comes out of the nucleusof atoms. • Radioactivity is when a substance spontaneously emits radiation. • loses energy by emitting radiation in the form of particles or electromagnetic waves. • There are several types of radiation emitted during radioactive decay.

  9. Radioactive Decay • Radioactive atoms (or radioisotopes) emit radiation because their nuclei are unstable. • Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. • Unstable radioactive atoms undergo radioactive decay until they form stable non-radioactive atoms. • An unstable nucleus releases energy to become more stable.

  10. Unstable Nuclei • any atom with more than 83 protons. • too much mass in the nucleus • causes isotope to release an alpha particle • too many neutrons in a nucleus • causes isotope to emit a beta particle • too many protons in a nucleus • causes isotope to emit a positron • too much energy in the nucleus • causes isotope release gamma rays

  11. Types of Radiation: Alpha, Beta, and Gamma • We are going to discuss three types of radiation. • The types are called alpha, beta, and gamma.

  12. Alpha Decay - α • Alpha particles are small particles of matter with a charge of +2 and a mass of 4 amu. • Alpha particle contains two protons and two neutrons – it is identical to the nucleus of a helium atom. • When an alpha particle slows down and gains two electrons it becomes a helium atom. • In a nuclear equation, is used to represent alpha decay. • Alpha Decay of U-238: • the mass drops by 4 amu and the atomic number by 2. • when U-238 undergoes alpha decay, it becomes Th-234.

  13. Examples - Alpha Decay • Uranium-235 emits an alpha • Ra-223 emits an alpha • Rn-219 emits an alpha

  14. Beta Decay • Beta particleswere also found to be particles. • Beta particles are simply high speed electrons. • When a beta slows down it becomes an electron. • In a nuclear equation, is used to represent beta decay. • Beta Decay of Th-234: • the mass remains constant and the atomic number rises by 1. • when a Th-234 undergoes beta decay it becomes Pa-234.

  15. Examples - Beta Decay • actinium-227 emits a beta • The decay of Fe-53 by beta emission.

  16. Gamma Decay • Gamma rays are not particles. • Gamma rays are high energy electromagnetic radiation. • They are photons (light) with no charge or mass so we simply write in our equations. • We write them as in our equations.

  17. Balancing Nuclear Reactions • the sum of the masses on the left of the arrow • Must equal the sum of the masses on the right of the arrow • the sum of the protons on the left • Must equal the sum of the protons on the right

  18. Summary of Radioactivity

  19. Emissions Penetrability Alpha particles stopped by a sheet of paper. Beta particles stop by aluminum shielding Gamma rays can only be reduced by much more substantial obstacles, such as a very thick piece of lead.

  20. Sources of Radioactivity • Primordial - from before the creation of the Earth • Cosmogenic - formed as a result of cosmic ray interactions • Human produced - enhanced or formed due to human actions (minor amounts compared to natural)

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