Nuclear Chemistry Lesson 1

Atomic Notation Sr 90 38 Recall, we learned atomic notation. A nuclide is the nucleus of a specific atom. The radioactive nuclide strontium-90 has 90 protons and neutrons. The atomic number is 38. Sr 90 38

Radioisotopes The nuclei of unstable isotopes gain stability by undergoing changes and emitting large amounts of energy (radiation) Nearly all isotopes with atomic number of 84 or greater are unstable

Band of Stability and Radioactive Decay

Transmutation The conversion of one atom to another is transmutation Artificial Transmutation – particles bombard the nucleus of an atom forcing a change. Natural Transmutation – the nucleus of an atom undergoes radioactive decay due to an imbalance between the number of protons and neutrons in a nucleus. Unstable atoms will decay until they create more stable atoms.

Mass Defect (Deficit) Some of the mass in the nucleus can be converted into energy (less than the mass of an proton) Shown by a very famous equation! E=mc2 Energy Mass Speed of light (a rather large number) ≈ 3 x 108 m/s In all nuclear reactions, some amount of mass is lost and converted into energy

Mass Defect Difference between the mass of an atom and the mass of its individual particles 4.00260 amu 4.03298 amu

Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleus. The nucleus opens, and protons and neutrons are rearranged. The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy “Normal” Chemical Reactions involve electrons, not protons and neutrons, therefore, comparatively little energy is gained from these reactions.

Types of Radiation Alpha (ά) – a positively charged helium nucleus Beta (β) – a.k.a. electron Gamma (γ) – pure energy; called a ray rather than a particle – has no mass or charge

Other Nuclear Particles Neutron Positron – a positive particle, same size as an electron Proton – usually referred to as hydrogen-1 And many other elemental isotopes

Charge of Radiation Types Alpha particles have a +2 charge, and beta particles have a –1 charge. Both are deflected by an electric field. Gamma rays are electromagnetic radiation and have no charge, so they are not deflected.

Penetrating Ability Video

Behavior of Radiation Since alpha particles have the largest mass, they are the slowest-moving type of radiation. Gamma rays move at the speed of light since they are electromagnetic radiation.

Alpha Radiation An alpha particle (a) or helium nucleus (42He) is emitted Each particle contains 2 protons, 2 neutrons and has a +2 charge (not usually written) 23892U  23490Th + 42He Note that the equation is balanced. The sum of the mass numbers & atomic numbers are equal.

Beta Radiation A beta particle (b) or electron (0-1e) is emitted A neutron breaks apart into a proton, which remains in the nucleus, and an electron, which is released 146C  147N + 0-1e Note that the equation is balanced. The sum of the mass numbers & atomic numbers are equal.

Gamma Radiation A gamma particle (g) or high energy photon is emitted (light) Gamma rays have no mass, no p+ and no no so they do not alter atomic mass or atomic number. It is PURE ENERGY which explains the large penetrating power of g rays. They are often emitted along with alpha or beta particles 23090Th  22688Ra + 42He + g

Electron Capture A few large, unstable nuclides decay by electron capture. A heavy, positively charged nucleus attracts an electron. The electron combines with a proton to produce a neutron. Lead-205 decays by electron capture. Pb 205 82 e -1 Tl 81 +

Balancing Nuclear Reactions The total of the atomic numbers (subscripts) on the left side of the equation must equal the sum of the atomic numbers on the right side. The total of the atomic masses (superscripts) on the left side of the equation must equal the sum of the atomic masses on the right side. After completing the equation by writing all the nuclear particles in an atomic notation, a coefficient may be necessary to balance the reaction. Use a particle or isotope to fill in the missing protons and neutrons.

Practice Problem 18579Au  18177Ir + 42He Write the nuclear equation for the alpha decay of gold-185. 18579Au  18177Ir + 42He

Practice Problem Fill in the blank. 21484Po  ___ + 0-1e + g 214At 85

Practice Problem Fill in the blank. 222Rn 86 21484Po + 2 42He + 2 0-1e  ___________  

Practice Problem What radioactive isotope is produced in the following bombardment of boron? 10B + 4He _____ + 1n 5 2 0 13N 7