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Nuclear Chemistry. Chemical vs Nuclear Reactions. Chemical reactions. Nuclear reactions. Occur when nuclei combine, split and emit radiation Can involve protons, neutrons and electrons Associated with large energy changes
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Chemical vs Nuclear Reactions Chemical reactions Nuclear reactions Occur when nuclei combine, split and emit radiation Can involve protons, neutrons and electrons Associated with large energy changes Atoms of one element are often converted into atoms of another element Temperature and pressure do not normally affect the rates of reactions • Occur when bonds are broken and formed • Involve only valence electrons • Associated with small energy changes • Atoms keep the same identity • Temperature, pressure and concentration all affect the rates of reactions
History of Nuclear Chemistry • In 1895, a German physicist Wilhelm Roentgen found that invisible rays were emitted when electrons bombarded the surface of certain materials • Caused photographic plates to darken
History of Nuclear Chemistry • Around this same time, the French physicist Henri Becquerel was studying minerals that emit light after being exposed to sunlight, called phosphorescence. • He wanted to see if his minerals emitted X-rays like Roentgens did • So he placed a uranium-containing mineral on top of a photographic plate and when he developed this plate he found a silhouette of the mineral • He concluded that the mineral was producing some kind of unknown radiation.
History of Nuclear Chemistry • Becquerel had two graduate students • A Chemist name Marie Curie and her husband Pierre Curie • They took Becquerel’s samples and isolated the components emitting the “rays” • They concluded that the darkening of the photographic plates was due to rays emitted from the uranium atoms present in the mineral sample • Marie called this process by which materials give off such rays as radioactivity
History of Nuclear Chemistry • The Curies identified two new elements on the basis of their radioactivity • Polonium • Radium • Becquerel and the Curies received the 1903 Nobel Prize in Physics and Marie received the 1911 Nobel Prize in Chemistry for her work with Po and Ra
History of Nuclear Chemistry • Remember this guy • He was responsible for the Gold Foil Experiment and his work discovered the electron • His name was Ernest Rutherford • Well he continued his research and discovered three new types of radiation • Alpha Radiation • Beta Radiation • Gamma Radiation
Getting rid of the cobwebs … • Nuclear Chemistry relies on some things we have previously learned • Isotopes – • Remember these are atoms of the same element that have different mass numbers • The atomic mass number on the periodic table is an AVERAGE of all the isotopes that exist for that element • We write isotopes in isotopic notation
Some new terms • In nuclear chemistry the term nuclide is often used. • A nuclide is the same thing as an isotope. • Same number of protons, different numbers of neutrons • Every element in the periodic table has at least one radioactive isotope, or radioisotope. • Radioactivity is the result of unstable nuclei, although the exact causes of this instability are not fully understood. • Radiation is emitted when an unstable radionuclide spontaneously changes into a more stable one.
Stable or Not Stable Isotope? • As elements get heavier the number of neutrons relative to the protons increases. • This unbalance causes elements with atomic number equal to or greater than 84 to take part in radioactive decay • Process where an unstable nucleus loses energy by emitting radiation to become more stable • When this happens the element changes into a new element, called transmutation
Fill in your table as we go through the types of particles that emit radiation
Alpha Radiation Alpha Emission • When an atom of uranium-238 emits an alpha particle, the nucleus loses two protons and two neutrons. • Because the number of protons in the nucleus has now changed from 92 to 90, the identity of the atom has changed from uranium to thorium.
Beta Radiation • Involves the decomposition of a neutron electron + proton. • The electron is ejected as a beta particle, and the proton is retained by the nucleus. • The atomic number of the atom increases by 1 because there is a new proton. • The mass number of the atom remains the same.
Gamma Radiation • Emission of gamma rays causes no change in mass or atomic number because gamma rays are simply high-energy electromagnetic waves. • Electromagnetic radiation (high energy) emitted from a nucleus as it changes from an excited state to a ground state. • It usually accompanies transmutation as a mechanism for the new nucleus to get rid of some extra energy. • Emission affects neither mass number nor atomic number • Gamma rays’ penetrating power makes them the most dangerous kind of external radiation and also makes them useful in medical applications.
