CHAPTER 25 Nuclear Chemistry I. The Nucleus -Terms (p. 798-820) II III IV

Ionizing Radiation Radiation is a form of energy transferred by waves or atomic particles Ionizing Radiation is any radiation with high enough energy to create ions (by knocking electrons out of atoms) like UV, X, gamma, and cosmic rays There are both natural sources of radiation (unstable nuclei and stars) and human created sources

Zone of Stability Stable nuclei exist within the “zone of stability” seen on the graph…not always a 1:1 ratio of p+ to no Outside this range, nuclei are unstable and will decay (disintegrate) into new nuclei

Definitions Nucleons = particles in nucleus (p+ and n0) Nuclide refers to the nucleus of an atom Nuclear Reactions involve transmutation where one element become another. Radioactive Decay is the when unstable nuclei spontaneous lose energy by emitting ionizing particles; as this changes the nucleus of the atom, this also changes the type of element

Alpha Decay Process  Daughter Nuclide Np-237 Th-234 Ra-228 Alpha decay is a radioactive process in which a particle with two neutrons and two protons is ejected from the nucleus of a radioactive atom. The particle is identical to the nucleus of a helium atom. Alpha decay only occurs in very heavy elements such as uranium, thorium and radium. The nuclei of these atoms are very “neutron rich” (i.e. have a lot more neutrons in their nucleus than they do protons) which makes emission of the alpha particle possible. After an atom ejects an alpha particle, a new parent atom is formed which has two less neutrons and two less protons. Thus, when uranium-238 (which has a Z of 92) decays by alpha emission, thorium-234 is created (which has a Z of 90). Because alpha particles contain two protons, they have a positive charge of two. Further, alpha particles are very heavy and very energetic compared to other common types of radiation. These characteristics allow alpha particles to interact readily with materials they encounter, including air, causing many ionizations in a very short distance. Typical alpha particles will travel no more than a few centimeters in air and are stopped by a sheet of paper. Show decay on chart of nuclides, Show smoke detector as application of alpha decay. Parent Nuclide Am-241 U-238 Th-232 Ra-226 Alpha Particle (Helium Nucleus) (4.00147 amu)

A. Mass Defect The mass defect describes the mass lost during the formation of nuclei Difference between the mass of an atom and the mass of its individual particles. 4.00260 amu Mass of atom 4.03298 amu Mass of particles

B. Nuclear Binding Energy Energy released when a nucleus is formed from nucleons. This contributes to the loss in mass of nucleus, described by E = mc2. High binding energy = stable nucleus. E = mc2 E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s)

B. Nuclear Binding Energy Iron (Fe) is the most stable nucleus!! Unstable nuclides are radioactive and undergo radioactive decay.

CHAPTER 25 Nuclear Chemistry II. Radioactive Decay (p. 798-820) II III IV

Types of Spontaneous Radiation stopped by… Greek symbol charge Alpha particle () helium nucleus paper 2+ Beta particle  or - electron 1- wood Positron + positron 1+ Lead or concrete Gamma () high-energy photon

Other Radiation particles Greek symbol charge proton p+ +1 neutron n0

How does an electron get emitted from the nucleus? Basically a neutron splits into a proton which stays in the nucleus and an electron is emitted ( decay) - + - + + + + n converted to a proton and an e is emitted n & p in nucleus n is “really” like a p and e together

Transmutation Reactions I Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance on both sides of arrow!! 238amu on left = (234 + 4amu) 92 is nucl chrg on left = 90 + 2 on right

B. Nuclear Decay II Beta Emission electron III Positron Emission *a proton 1p is not the same as a positron 0e

B. Nuclear Decay IV Electron Capture electron

B. Nuclear Decay Alpha capture V Alpha Capture followed by neutron emission Alpha capture Gamma Emission causes no change in mass or charge and… Usually follows the previous types of decay.

Beta (Negatron) Decay Process Daughter Nucleus Osmium-187 Calcium-40  Antineutrino Beta decay is a radioactive process in which an electron is emitted from the nucleus of a radioactive atom, along with an unusual particle called an antineutrino. The neutrino is an almost massless particle that carries away some of the energy from the decay process. Because this electron is from the nucleus of the atom, it is called a beta particle to distinguish it from the electrons which orbit the atom. Like alpha decay, beta decay occurs in isotopes which are “neutron rich” (i.e. have alot more neutrons in their nucleus than they do protons). Atoms which undergo beta decay are located below the line of stable elements on the chart of the nuclides, and are typically produced in nuclear reactors. When a nucleus ejects a beta particle, one of the neutrons in the nucleus is transformed into a proton. Since the number of protons in the nucleus has changed, a new daughter atom is formed which has one less neutron but one more proton than the parent. For example, when rhenium-187 decays (which has a Z of 75) by beta decay, osmium-187 is created (which has a Z of 76). Beta particles have a single negative charge and weigh only a small fraction of a neutron or proton. As a result, beta particles interact less readily with material than alpha particles. Depending on the beta particles energy (which depends on the radioactive atom), beta particles will travel up to several meters in air, and are stopped by thin layers of metal or plastic. Show compact fluorescent light bulb as application of beta decay. Parent Nucleus Rhenium-187 Potassium-40  Beta Particle (electron)

Beta Particles Same as an electron with kinetic energy Positive or negative charge of 1 May be positively or negatively charged Can normally be stopped by 1 cm of plastic, wood, paper Exception for positron emitters

B. Nuclear Decay Why nuclides decay…pg. 803 need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY

C. Half-life Half-life (t½) Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable.

C. Half-life mf: final mass mi: initial mass n: # of half-lives

C. Half-life t½ = 5.0 s mf = mi (½)n mi = 25 g mf = (25 g)(0.5)12 Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g

Decay Series Many heavy elements are unstable and so they will continue to decay (be radioactive) until they finally transmute into a stable nucleus. Here is an example of the Th-232 decay series Thorium oxide is used to in camping lanterns to intensify the brightness when on fire. Stable isotope