CHEM 1120 1st Edition Lecture 9 Outline of Last Lecture 1 Cell theory 2 How we study cells 3 Common features of cells 4 Prokaryotic cells features 5 Eukaryotic cells features Outline of Current Lecture 1 Chemical Reactions vs Nuclear 2 Radioactivity 3 Balancing Nuclear 4 Types of Emissions 5 Nuclear Stability Current Lecture Chapter 21 Nuclear Chemistry Energy Chemical vs Nuclear o Chemical energy associated with making and breaking chemical bonds o Nuclear energy Is enormous in comparison o Nuclear energy due to changes in nucleus of atoms changing them into different atoms o 13 worldwide energy comes from nuclear energy Chemical Reactions These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute o o Atoms never change identity Chemical bonds break and form with changes in distribution of orbital electrons Nuclear particles do not take part o Small changes in energy and immeasurable change of mass o Reaction rates are sensitive to reactants temperature reactant concentration and catalysis Nuclear reaction o Atoms of one element typically convert into atoms of another element o Protons neutrons and other elementary particles are involved Orbital electrons rarely take part o Large changes in energy and measurable mass changes occur o Reaction rates affected by number of nuclei not by reactant temp concentrations and catalysis 12 1 Radioactivity the spontaneous emission of particles or radiation from atomic nuclei A stable nucleus remains intact indefinitely but great majority of nuclei are unstable An unstable nucleus exhibits radioactivity it spontaneously disintegrates or decays Protons and neutrons o Elementary particles that make up the nucleus are collectively called nucleons Nuclide o Nucleus with a particular composition of mass number and atomic number Nucleon o A proton or neutron Radionuclide o A nuclide that is radioactive Radioisotope o An atom containing a radionuclide X symbol for element Z charge of particle number of protons A mass number mass sum of nucleons protons and neutrons Balancing Nuclear Equations In an equation atoms and charges need to balance Atomic number and mass number need to balance When nuclide decays forms a nuclide of lower energy and the excess energy is carried off by the emitted radiation o The decaying or reactant nuclide is called the parent o The product nuclide is called the daughter REACTANTS TOTAL A Z PRODUCTS TOTAL A Z Types of Emissions Radiated emitted by a radionuclide Radioactive decay is when a nuclide of one element spontaneously decays into a nuclide of a different element Three common types of emission radiation o Alpha o Beta o Gamma Types of Radioactive decay o Alpha Loss of an alpha particle from a nucleus For each particle emitted A decreases by 4 and Z decreases by 2 Every element heavier than Pb Z 82 as well as a few lighter ones exhibits alpha decay o Beta Involves the ejection from a beta particle from the nucleus Conversion of a neutron into a proton which remains in the nucleus and a beta particle which is expelled immediately o Positron Involves the emission of a positron from a nucleus Positron is the antiparticle of an electron Involves the conversion of a proton into a neutron o Electron capture Occurs when the nucleus of an atom draws in an electron from an orbital of the lowest energy level Involves conversion of a proton into a neutron o Gamma Involves the radiation of high energy gamma photons from an excited nucleus 21 2 Patterns of Nuclear Stability Why only some isotopes radioactive o For smaller nuclei Z is smaller than or equal to 20 stable nuclei have a neutron toprotons ratio close to 1 1 o As nuclei get larger it take a larger number of neutrons to stabilize the nucleus o 265 isotopes are stable all lie in a belt of stability o Nuclei with 83 protons are all radioactive o Magic numbers nuclei with 2 8 20 28 50 or 82 protons or neutrons are favored