Nuclear Chemistry

Nuclear Chemistry

Nuclear Chemistry Lesson 1 Atomic Notation Recall, we learned atomic notation. The radioactive strontium-90 has 90 protons and neutrons. The atomic number is 38. 90 38 Sr 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! Energy

2 E=mc 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 4 Alpha () a positively ) a positively He 2 2 charged helium nucleus 4 2 0 Beta () a.k.a. electron) a.k.a. electron 1e Gamma () pure energy; ) pure energy;0 1 0 called a ray rather than a1 0 particle has no mass or 0 0

charge 0 He e Other Nuclear Particles 1 Neutron 0n Positron a positive particle, same size as an electron Proton usually

referred to as hydrogen-1 1 0 0 0 01 e1 1 1 1 H 1 1 n

e H 1 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) 238 92U

234 90 Th + 4 He 2 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 14 6C 14 7 N+ 0 -1

e Note that the equation is balanced. The sum of the mass numbers & atomic numbers are equal. Gamma Radiation A gamma particle () 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 rays. They are often emitted along with alpha or beta particles

230 226 4 Th Ra + 90 88 2He + 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. 205 82 Pb + 0 -1 e 205 81 Tl

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 Write the nuclear equation for the alpha decay of gold-185. 185 79Au Ir + 181

77 4 2 He Practice Problem Fill in the blank. At 214 85 Po ___ +

214 84 0 -1 e+ Practice Problem Fill in the blank. Rn 222 Po + 2 42He + 2 0-1e

214 84 86 ___________ Practice Problem What radioactive isotope is produced in the following bombardment of boron? N _____ + 1n 7 13

B 10 5 + He 4 2 0

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