AP CHEMISTRY 1. Clear your desk except for something to write with 2. Homework: 1. Complete the online quiz by 9 pm tonight. 2. Complete the chapter 21.1 and 21.4 note card. 3. Titration lab report due on Thursday 10/21

Review Exam

 What can you recall about radioactivity?

Review of element shorthand Remember that the nucleus is comprised of the two nucleons, protons and neutrons. The number of protons is the atomic number. The number of protons and neutrons together is effectively the mass of the atom. Write the short hand for U and Ga.

Key concepts in radioactivity  Nucleons  Mass Number  Atomic Number  Isotopes  Short hand for isotopes

 Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms.  There are, for example, three naturally occurring isotopes of uranium:  Uranium-234  Uranium-235  Uranium-238

Nuclear Equations  Alpha Particles ( α)  Unstable and emit Helium – 4 particle  When alpha particles form, radioactive decay has occurred.  Part of the product is :  Example: U-238  Notice that the total number of protons and neutrons on the reactant side is the same as the product side. U  U He

Beta Decay/Emission  Beta particles ( β)  A neutron is converted to a proton and electron.  β emission/decay Generic equation: Example: β emission for Th – 231 Write the equation for beta emission for I-131  0−10−1 e 0−10−1 or I Xe  + e 0−10−1

Positron Emission  Positron emission same mass as an electron, but a different charge Generic equation: Example: positron emission for Th-231 Example: Write the positron emission for C-11 e 0101 C 11 6  B e 0101

Electron Capture  Electron capture Addition of an electron to a proton in the nucleus is known as electron capture The result of this process is that a proton is transformed into a neutron. Generic equation: Example: electron capture for Rb-81 e 0−10−1

Gamma Radiation  This is the loss of a  -ray, which is high-energy radiation that almost always accompanies the loss of a nuclear particle.  0000 U  U He  0000

CW  Show the nuclear equations for the following problems  Page 896 – practice exercise25-9  Page 925 #21.11  Homework: Page 926 # to 14

Rates of Decay  Table 21.4  This table shows the half-life for various radioactive isotopes.  The half-life is the amount of time for half of the radioisotope to decay.  Example: If I have a 125 g sample of Cs-137, how much of a sample is left after 120 years?

Rates of Decay  Example: If I have 400 g of Sr-90, what is the percentage left after 86.4 years?  Try Practice Exercise on page 904.

Homework  Page  21.33, 21.34, 21.35, 21.36