The spontaneous emission of radiation › Created by unstable nuclei of very heavy elements › Radioactive elements can give off 3 types of radiation: Alpha: helium nuclei can usually be stopped by a piece of paper Beta: e- which are much smaller and lighter than alpha particles More penetrating power than alpha particles Can be stopped by a thick wooden board Gamma Extremem energetic form of light VERY powerful Several inches of lead of several feet of concrete necessary to stop them
Atomic Number: › is the number of protons in the nucleus › The Lithium atom has three electrons occupying 2 energy levels and three protons giving it an atomic number Z = 3. Atomic Mass: › is the number of particles in the nucleus. › The Lithium nucleus includes four neutrons and 3 protons making up its seven particles and thus a mass number A = 7 Atomic Structure: › Lithium-7 or 7 Li › The mass number is placed after the name of the element or is indicated as a superscript preceding the chemical symbol. › 7 Li 3 › The symbol may also indicate the full atomic structure by adding a subscript representing the atomic number.
Write the nuclear notation for the following: Li U Pb
Uranium-238 decays to form Thorium-234, a radioactive silvery metal, with the emission of one Helium atom. Thus 238 U 92 ⇒ 234 Th He 2 The daughter nuclide (thorium-234) has 2 fewer protons and neutrons than the parent nuclide (uranium-238)
A radioactive elements distinctive rate of decay The amount of time it takes ½ of radioactive material to decompose
A radioactive isotope has a half-life of 12.4 hours. If a lab starts with a 13.2 mg sample how much will remain after 37.2 hours? 13.2/2 /2 /2 = 1.65 mg A radioactive substance has a half-life of 10 years. How much is left after 30 years? ½ of ½ of ½ or 1/8
Procedure and Questions 1&2 Monday April 18
Wednesday April 20
The fission process take place when the nucleus of a heavy atom, like uranium or plutonium, is split in two when struck by a neutron. The "fissioning" of the nucleus releases two or three new neutrons.
1 0 n U Sn Mo n 1 neutron bombards 1 heavy element and it disintegrates into 2 smaller nuclei and 2-3 neutrons
4 1 1 H e 4 2 He
All Group Analysis Questions Wednesday April 20