NAME PERIOD DATE CHAPTER 4 NOTES: ISOTOPES Isotopes and Radioactive Decay ISOTOPES: Atoms that contain the same number of protons but a different number of neutrons. Isotopes containing more neutrons have a greater mass. Despite the difference in mass, isotopes of an atom will have the same chemical behavior. Generally in nature most elements are found as mixtures of isotopes. An example of this can be found with the Potassium (K) in a banana. 93.26% of the potassium atoms have 20 neutrons, 6.73% of the potassium atoms have 22 neutrons, and 0.01% of the potassium atoms have 21 neutrons. ATOMIC MASS: The weighted average mass of the isotopes of a certain element. Atomic mass is expressed in units of atomic mass units (amu), which is defined as the one-twelfth the mass of a carbon atom. 1 amu is nearly equal to the mass of a single proton or a single neutron. ISOTOPE/NUCLEAR NOTATION:
ISOTOPE/NUCLEAR NOTATION FOR THE 3 ISOTOPES OF HYDROGEN: Given the data in the table, calculate the atomic mass of unknown Element X: ISOTOPE ABUNDANCE FOR ELEMENT X Isotope Mass (amu) Percent abundance 6 X 6.015 7.59% 7 X 7.016 92.41% Ex #1): Write nuclear symbols for 3 isotopes of carbon (atomic number = 6) in which there are 6, 7, and 8 neutrons respectively. Ex #2): A radioactive isotope that is used for radiation treatment of cancer is the Cobalt 60 atom. How many protons are there? How many neutrons are there? RADIOACTIVE DECAY NUCLEAR REACTION: Reaction that can change an element into a new element. It requires a change in an atom s nucleus.
Radiation is the rays and particles emitted by radioactive materials. Radioactive atoms emit radiation because their nuclei are unstable. Radioactive decay is a spontaneous process in which unstable nuclei lose energy by emitting radiation. Radioactive decay will continue to occur until a stable atom has formed, which is often a different element altogether. The most important factor in determining an atom s stability is its ratio of neutrons to protons. Nuclei are unstable when there are either too many or too few of protons or neutrons. Types of Radiation: o ALPHA RADIATION: Radiation that is made up of alpha particles. An alpha particle contains 2 protons and 2 neutrons and has a 2+ charge. An alpha particle is equivalent to a helium-4 nucleus. Alpha particles are represented by or. Example of alpha radiation (the following equation is an example of a nuclear equation): o BETA RADIATION: Radiation that is made up of beta particles. A beta particle contains an electron with a 1- charge. Beta particles are fast-moving. Beta particles are represented by the symbols e- or.
Example of beta radiation (the following equation is an example of a nuclear equation): o GAMMA RADIATION: Radiation that is made up of gamma rays. A gamma ray is high-energy and contains no mass and is represented by the symbol. Gamma rays usually accompany alpha and beta radiation. Gamma rays also account for most of the energy lost during radioactive decays. Since gamma radiation is massless the emission of gamma rays cannot end in the formation of a new atom. Example of gamma radiation (the following equation is an example of a nuclear equation): Characteristics of Radiation: Alpha Beta Gamma Symbol Mass (amu) 4 1/1840 0 Charge 2+ 1-0 HOMEWORK PRACTICE PROBLEMS: 1. Which subatomic particle identifies an atom as that of a particular element? 2. An element contains 66 electrons. Which element is it?
3. An element contains 14 protons. Which element is it? 4. Boron (B) has two naturally occurring isotopes: boron-10 (abundance = 19.8%; mass = 10.013 amu) and boron-11 (abundance = 80.2%; mass = 11.009 amu). Calculate the atomic mass of boron. 5. Copper has two isotopes: Cu-63 (abundance = 69.2%; mass = 62.930 amu) and Cu-65 (abundance = 30.8%; mass = 64.928 amu). Calculate the atomic mass of copper. 6. Three magnesium isotopes have atomic masses and relative abundances of 23.985 amu (78.99%), 24.986 amu (10.00%), and 25.982 amu (11.01%). Calculate the atomic mass of magnesium. 7. Nitrogen has two naturally occurring isotopes, N-14 and N-15. Nitrogen s atomic mass is 14.007. Which isotope is more abundant and WHY? 8. Boron-10 emits alpha particles. Write a balanced nuclear reaction for this radioactive decay.
9. Cesium-137 emits beta particles. Write a balanced nuclear reaction for this radioactive decay. 10. Iodine-121 emits alpha particles. Write a balanced nuclear reaction for this radioactive decay.