Nuclear Chemistry

Isotopes When an atom or element can be found somewhere on Earth, it is called naturally occurring. Of the 118 elements on the periodic table, 92 are naturally occurring; the rest exist only as a result of human activity or unusual circumstances. Some elements have only one isotope, but most have more than one.

Stable vs. Radioactive Isotopes Stable isotopes have a stable nucleus. Stable = balance between the number of protons and neutrons in a nucleus Too few or too many neutrons will lead to the disintegration of an atom. The larger the atom, the more neutrons it takes to make a stable nucleus. Radioactive Isotopes Not stable Emit small particles (neutrons, protons, electrons, and odd mixes or variations of these particles). Called radioactive isotopes. not common; the majority of radioactive isotopes are elements with atomic numbers above 80.

Why are some substances radioactive? What is radiation???? Why are some substances radioactive?

Nuclear Chemistry Radiation: particles emitted from the nucleus Substances are radioactive because the neutron to proton ratio is “off” Radioactive substances emit radiation in order to get at n0: p+ ratio that is stable (low energy) Band of Stability

Nuclear Radiation Radioactivity: particles or radiation emitted from a nucleus during radioactive decay Radioactive Decay: the spontaneous break-down of a nucleus into a slightly lighter nucleus, accompanied by the emission of nuclear radiation

Types of Nuclear Radiation 1. alpha particles 2. beta particles 3. gamma rays Ionizing Radiation: can ionize atoms that they hit Emission of these types of particles (nuclear reactions) involve changes to the nucleus of the atom!

Alpha Radiation (α) 2 protons & 2 neutrons bound together. Nucleus of a helium atom Symbol 42He Particles do not travel far and are not very penetrating Particles can be stopped by a piece of paper! 238 92 U 234 90 Th + 4 2 He

Beta Radiation (β) An electron that has been ejected from the nucleus Formed when a neutron breaks down into a proton and electron Has a charge of -1 Mass 1/1837 amu Symbol: 0-1e or β Can pass through paper, but not aluminum foil or wood 14 6 14 7 -1 C N + e

Gamma Radiation (γ) high-energy photon emitted by a radioisotope is a gamma ray (). often emitted along with alpha or beta particles during radioactive decay. have no mass and no electrical charge. extremely penetrating; can be stopped, although not completely, by several centimeters of lead.

In your notebook..... 1. Sketch the picture below 2. Identify the type of radiation being depicted. A B C

In your notebook..... 1. Sketch the picture below 2. Identify the type of radiation being depicted.

Balancing Nuclear Equations - follows law of Conservation of Mass -mass numbers for products and reactants have to equal. -atomic numbers for products and reactants have to equal. 37+0 = 37 20+ -1 = 19

Balance the following nuclear equations by adding the correct particle, and complete the sentence (copy these into your notebook!) Uranium-235 undergoes _____________ decay Radium 226 undergoes _____________ decay Technecium-99 undergoes _____________ decay

Writing nuclear equations Write a balanced nuclear reaction for the following: 1. Potassium-37 undergoes beta decay. 2. Polonium-210 undergoes alpha decay.

Half Life Is the time required for one-half of a sample to decay (really, to change into another element). For example, it takes 5730 years for half of a sample of carbon-14 to decay into nitrogen-14 through beta decay.

Calculate Half Life Final Amount Time AF = AI * (.5) t/h Half-Life Initial Amount Half-Life

Give it a try An isotope of cesium (cesium-137) has a half-life of 30 years. If 1.0 mg of cesium-137 disintegrates over a period of 90 years, how many mg of cesium-137 would remain?

Fission & Fusion

Fusion Fusion: when two small nuclei combine to form a larger more stable nucleus Ex.: energy from the sun comes from nuclear fusion

Fission Fission: a large nucleus splits apart into lighter more stable nuclei Ex.: type of reaction that occurs in a nuclear reactor