Nuclear Chemistry EQ: How does Nuclear chemistry affect the structure of atomic nuclei? Ch 25 CVHS

Why do atoms emit radiation? The nucleus is unstable due in part to the ratio of protons and neutrons Atoms that emit particles are radioisotopes Atoms emit radiation & lose energy = more stable

Types of Radiation Alpha (α): Positive particle bends toward neg. plate Beta (β): Neg. charge, bend toward positive, less massive than alpha so they bend more Gamma (γ): Not charged don’t bend

Alpha Particle Same as a He nucleus 2+ charge, b/c of 2 protons Alpha radiation: stream of alpha particles Large, slow moving, stopped by a sheet of paper After the decay, the atom is no longer Radium WHY? Different # of protons, it is now radon-218 Ra Atomic # & Mass # must be equal on both sides.

Beta Radiation Mass # stays the same Atomic # increases by 1 Fast moving electron Emitted from neutron of unstable nucleus Light weight, fast moving Aluminum foil stops them Negative charge Notice that the # of protons in the nucleus increases by 1, so a new element is formed A neutron splits, the proton stays in the nucleus and the high energy electron (beta particle) leaves Mass # stays the same Atomic # increases by 1

Gamma Radiation High Energy, short wavelength, electromagnetic radiation No mass & no charge Energy that accompanies alpha & Beta radiation Gamma symbols are typically omitted from nuclear equations b/c they have no impact on mass or charge

Nuclear Stability Protons repel eachother b/c they are positively charged. Small Effect: Ratio of Protons to neutrons For atoms with low atomic numbers (< 20), the most stable nuclei are those with neutron-to-proton ratios of 1 : 1, Neutron to proton ratio increases to a max of 1.5 : 1; all atoms above 83 Bi are radioactive STRONG NUCLEAR FORCE : a force that overcomes the electrostatic repulsion of the positively charged protons Acts only on subatomic particles

Balancing Nuclear Equation Practice Write a balanced nuclear equation for the alpha decay of thorium-230 Reactant: Thorium 230, products: X & alpha particle Make sure that the atomic numbers and masses are equal on both sides of the equation: Law of Conservation of Mass then look up the new element formed by it’s atomic number (protons) on the periodic table. Notice: 230 = 226 + 4 and 90 = 88 + 2 so mass is conserved

Beta Decay Practice What element is formed when undergoes beta decay? Give the atomic number and mass number of the element.  X + What is X? It has to have an atomic number that equals 26 when we subtract 1. Atomic # 27 is Cobalt.  + Write a balanced nuclear equation for the beta decay of the following radioisotope

Half Life A half-life is the time required for one-half of a radioisotope’s nuclei to decay into its products strontium-90 Half Life = 29 10.0 g today = 5.0 g in 29 years

Calculating a half life Where t is the elapsed time and T is the duration of the half-life, must be in the same units.

Practice The half-life of iron-59 is 44.5 days. How much of a 2.000-mg sample will remain after 133.5 days? Divide time passed by duration of half life 133.5/44.5 = 3 3 half lives have passed Divide 2 in half 3 times 2/2=1 1/2= .5 .5/2=.25 .25 g remain after 133.5 days Substitute the values for n and initial mass into the exponential decay equation and solve

C 14 Dating

Nuclear Fission Splitting of nucleus into fragments Large atoms Releases large amt of energy Critical mass creates a chain reaction Nuclear power plants harness the energy released by fission reactions Heat generates steam Steam powers turbines to generate electricity Cadmium and Boron rods keep the reaction under control by absorbing the atomic particles that are released

Nuclear Fusion Combining of atomic nuclei Occurs on the sun Thermonuclear reactions Release a large amt of energy but happen at very HIGH temperatures Occurs on the sun Scientists use to create new atoms