Nuclear Chemistry Essential Question: How do we determine stability of a nucleus to compare different atoms?

TN Science Standards Chemistry I : Standard 1 – Atomic Structure CLE 3221.1.3 Describe an atom in terms of its composition and electron characteristics. 3221.1.7 Determine the number of protons and neutrons for a particular isotope of an element.

Mass Defect The difference between the mass of a nuclide and the sum of masses for all of its protons, neutrons, and electrons The atom always has less mass…why? Consider

Mass Defect Sum total mass of all particles in 2 protons (2 x 1.007276 amu) = 2.014552 amu 2 neutrons (2 x 1.008665 amu) = 2.017330 amu 2 electrons (2 x 0.000548 amu) = 0.001097 amu ________________________________________ total mass of all particles = 4.032 979

Mass Defect Sum of parts is 4.032979 amu Isotope’s relative mass is 4.002602 amu Mass defect = difference 0.030377 amu What happened to the “missing” mass?

Nuclear Binding Energy The energy released when a nucleus is formed from protons and neutrons Considered the energy required to hold a nucleus together More energy released = more stable nucleus! So what is the source of this energy released from the nucleus?

Nuclear Binding Energy Recall E=mc2 Mass defect 0.030377 amu from converts into 4.54 x 10-12 Joules of nuclear binding energy

Nuclear Binding Energy Binding energy is used to compare stability of different nuclides The total nuclear binding energy calculated from mass defect with E=mc2 is divided by mass number and graphed

Nuclear Stability A graph of stable nuclei cluster along a narrow band n° : p+ 1.5 : 1 For Z ˃ 20 A graph of stable nuclei cluster along a narrow band Called the “Band of Stability” Notice two slopes… Black line m=1 for small atoms Red line m= 1.5 for larger atoms (A-Z)/Z = 1.5 n° : p+ 1 : 1 For Z ˂ 20

Nuclear Stability Stable nuclei have even mass numbers Most have even numbers of both protons and neutrons Magic Numbers 2, 8, 20, 28, 50, 82, and 126 These numbers of p+, n°, or both are most stable by completing nuclear energy levels

Nuclear Stability Unstable nuclei spontaneously decay to become more stable Nuclear Reaction a reaction that changes a nucleus of an atom Transmutation a change in the identity of an atom when the number of protons are changed