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Chapter 4 - Isotopes and Radioactive Decay

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Sydney Sturgeon

on 5 October 2015

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Transcript of Chapter 4 - Isotopes and Radioactive Decay

Chapter 4 - Isotopes and 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.
Example #1: Write nuclear symbols for 3 isotopes of carbon (atomic number = 6) in which there are 6, 7, and 8 neutrons respectively.
Definition: 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 one-twelfth the mass of a carbon atom.

1 amu is nearly equal to the mass of a single proton or a single neutron.
Definition: 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 bananas. 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.
Nuclear symbols for the 3 isotopes of Carbon:
Calculate the atomic mass of unknown Element X using the relative abundance of each isotope:
Isotope X: Mass = 6.015 amu; Percent Abundance = 7.59%
Isotope X: Mass = 7.016 amu; Percent Abundance = 92.41%
Example #2: A radioactive isotope that is used for radiation treatment of cancer is the Cobalt-60 atom. How many protons and neutrons are there?
The 60 attached to Cobalt is the Atomic Mass Number.

Atomic Mass Number = # of protons + # of neutrons

Cobalt's Atomic Number = 27

# of protons = 27

# of neutrons = 60-27 = 33
Atomic Mass = (mass of X)(% abundance of X) + (mass of X)(% abundance of X)

Atomic Mass = (6.015 amu)(0.0759) + (7.016 amu)(0.9241)

Atomic Mass = 0.4565385 amu + 6.4834856 amu

Atomic Mass = 6.9400241 amu

Atomic Mass = 6.94 amu
Once you have your answer write it on your whiteboard.
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 protons or neutrons.
As the atomic number increases you want a smaller ratio meaning you want less protons to neutrons.
Types of Radiation: 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
Example of alpha radiation:
Types of Radiation: 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
Example of beta radiation:
Types of Radiation: 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:
Types of Radiation Review: Characteristics of Radiation
Mass = 4 amu; Charge = 2+
Mass = 1/1840 amu; Charge = 1-
Mass = 0 amu; Charge = 0
Before you sit down pick up the following from the demo table:
1. Isotopes and Radioactive Decay NOTES (white)
2. Nuclear Chemistry - Characteristics of Radiation TABLE (red)
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