SCIENCE 10: (7.1) ATOMIC THEORY, ISOTOPES AND RADIOACTIVE DECAY Name: Date: Block: (Textbook Reference pp. 286-301 in BC Science 10) Natural background radiation: It has the ability to interact with an atom and turn it into an Radiation: When atoms lose high-energy particles and waves, ions or even new atoms can be formed. High-energy waves and particles are called radiation when they leave the atom. Radioactivity: Being exposed to radioactive materials can be beneficial or harmful. Beneficial: Harmful:
ISOTOPES AND MASS NUMBER Isotopes:. Remember that an atom of an element will have the same number of protons and electrons ( ) Not all atoms of an element have the same number of neutrons ( ). Remember the mass number tells you the total number of and in an isotope. Isotopes of an element have the same and same Mass number = + Atomic mass =. REPRESENTING ISOTOPES http://www.colorado.edu/physics/2000/isotopes/index.html Isotopes are written using standard atomic notation. The standard atomic symbol (or nuclear symbol) for the following isotopes of potassium would be: o Potassium-39 o Potassium-40 o Potassium-41
In nature, most elements are found as a mixture of isotopes. http://www.chem4kids.com/files/atom_isotopes.html Complete the Practice Problems on p. 291 RADIOACTIVE DECAY Radioactive decay: Radioactive atoms release energy until they become, often as different atoms. Ex. Uranium -238 undergoes 14 different radioactive decay steps before forming stable lead-206.
An element may have only certain isotopes that are radioactive. Isotopes that are capable of radioactive decay are called. THREE TYPES OF RADIATION Rutherford identified three types of radiation using an electric field. Positive were attracted to the negative plate. Negative were attracted to the positive plate. Neutral did not move towards any plate. ALPHA RADIATION Alpha radiation is a stream of particles. They are charged, and are the massive of the radiation types. Alpha particles are essentially the same as atoms. Alpha particles are represented by the symbols: Because it has two protons, it has a charge of
The release of alpha particles is called. Alpha particles are and penetrate materials much than the other forms of radiation. A sheet of will stop an alpha particle. Example: ***Note: The equation is balanced! (The sum of the atomic numbers and the sum of the mass numbers are equal on both sides of the arrow. Also the product nucleus has an atomic number that is lower by two and a mass number that is lower by four due to the alpha particle) Complete the Practice Problems on p. 295
BETA RADIATION A beta particle is an and is charged. Beta particles are represented by the symbols: Electrons are very tiny, so beta particles are assigned a mass of. Since there is only an electron, a beta particle has a charge of. Beta decay occurs when a changes into a + an. The proton stays in the nucleus, and the electron is. It takes a thin sheet of to stop a beta particle. Example: ***Note: The equation is balanced! (The sum of the atomic numbers and the sum of the mass numbers are equal on both sides of the arrow. Also the product nucleus has an atomic number that is greater, making it an atom of the next higher element and a mass number that equal to the reactant because the beta particle emitted was an electron)
Complete the Practice Problems on p. 296 GAMMA RADIATION Gamma radiation is a of high-energy, short-wavelength radiation. Gamma radiation has charge and mass, and is represented by the symbol Gamma radiation is the -energy form of electromagnetic radiation. It takes thick blocks of or to stop gamma rays. Gamma decay results from being released from a high-energy nucleus. Often, other kinds of radioactive decay will also release gamma radiation. Uranium-238 decays into an alpha particle and also releases gamma rays. Example: ***Note: The equation is balanced! (The sum of the atomic numbers and the sum of the mass numbers are equal on both sides of the arrow. Also the product nucleus has an atomic number and a mass number that are equal to the reactant because gamma decay involves energy, not particles.)
SUMMARY: Type ALPHA BETA GAMMA RADIATION RADIATION RADIATION Symbol Particle or Ray Description of Radiation Charge Relative mass Chemical symbol Can be stopped by: ALPHA DECAY BETA DECAY GAMMA DECAY Particle emitted Change in mass of starting nucleus. Change in atomic number of starting nucleus. Remember the following rules when you write a nuclear equation: 1. 2. More Practice: Complete p. 301 #4, 7, 11-13