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How do you know if an atom is stable?
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In this video, we're going to learn about radioactive decay.
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An atom is composed of subatomic particles called protons, neutrons, and electrons.
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Positively charged protons, the neutrons with no charge from the central nucleus.
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Negatively charged electrons orbit the nucleus.
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For more information on atomic structure, watch this video.
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A strong nuclear force holds the positive protons and neutral neutrons together in the nucleus
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and is what determines if a nucleus is stable.
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In stable nuclei, the force is strong enough and brings sufficient energy to hold the nucleus together permanently.
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Most of the nuclei formed during the Big Bang nearly 14 billion years ago are still in existence today,
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but not all nuclei are stable.
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Unstable nuclei either have too many protons or too many neutrons
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upsetting the strong nuclear forces.
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Unstable nuclei try to balance themselves by giving off the excess proton or neutron.
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This is radioactive decay.
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Unstable nuclei are radioactive and emit radiation.
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There are three types of decay.
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Alpha decay, Beta decay (minus), or Beta decay (positive).
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Alpha decay is the loss of an Alpha particle.
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An alpha particle is made of 2 neutrons and 2 protons.
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They have a mass of 4 and a charge of +2.
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When an atom loses an Alpha particle,
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the mass number decreases by 4 and the atomic number decreases by 2.
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A new element is formed that is 2 places lower in the periodic table.
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When an isotope has too many neutrons, it decays by Beta minus decay.
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A neutron changes into a proton and an electron.
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The proton is retained by the atom while the electron is lost.
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The lost electron is high-energy and is called a Beta particle.
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By losing a neutron whilst gaining a proton,
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the mass number of the atom remains the same,
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but the atomic number increases by 1.
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A new element is formed, that is 1 place higher in the periodic table.
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When an isotope has too many protons, it decays by Beta plus decay.
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A proton is converted into a neutron and a positive Beta particle called a positron.
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Positrons have the same mass as electrons but the opposite charge.
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By losing a proton but gaining a neutron,
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means the mass number stays the same.
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But the loss of a proton means the atomic number decreases by 1.
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So how do we know if an atom is stable or unstable?
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We can determine whether a radioisotope is likely to decay and what type of decay is likely to occur
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by looking at its position on a proton-neutron NZ graph.
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This graph shows the number of protons on the x-axis
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and the number of neutrons on the y-axis.
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This is a stability line.
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If a radioisotope lies left or right of this line,
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it is unstable and likely to decay to become stable.
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A radioisotope that lies to the left of the stability line
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has too many neutrons and is likely to undergo Beta minus decay, so give off electrons.
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A radioisotope that lies to the right of the stability line has too many protons
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and is likely to undergo Beta plus decay, so give off positrons.
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If particles have a high number of protons, usually more than 82,
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they are likely to undergo Alpha decay.
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In this video, we have learned that unstable nuclei either have too many protons or too many neutrons,
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which upsets the strong nuclear force holding the atom together.
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Unstable nuclei try to balance themselves by giving off the excess proton or neutron
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either through Alpha, Beta minus, or Beta plus decay.
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Comment below if you have any questions.
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Until next time!