Download Concept Review 3.1 Introduction to Nuclear

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Ch3 Notes Page 1
Ch3 Section 1 Introduction to Nuclear Chemistry
Nucleus
 Made up of Protons and Neutrons collectively called nucleons (particles in the nucleus)
 Small particles that make up protons and neutrons are called quarks
Atom
 In nuclear chemistry the atom is called the Nuclide
 Identified by the number of protons and neutrons in its nucleus
 Nuclides are represented two ways:
1) Radium-228
name of element followed by atomic mass (which is the # of protons + neutrons)
2) 228
(atomic mass)
Ra (symbol) as well as the # of electrons)
88
(atomic number which is the # of protons)
 Isotope: An element with the same number of protons but a different number of neutrons
(Also, An element with the same atomic number but a different mass number)
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Nuclear Forces
Electrostatic Force – Like charges repel (+, + and -, -) and opposite charges attract (-, +).
 As the number of protons in a nucleus increases, the repulsive electrostatic force between protons increases
faster than the nuclear force. More neutrons are required to increase the nuclear force and stabilize the
nucleus.
Strong Force – holds the protons and neutrons (nucleons) together in a nucleus, resisting the positive protons
from repelling each other as long as these particles are very close together.
 Beyond the atomic number 83 (Bismuth), the repulsive force of the protons is so great that no stable
nuclides exist.
 In larger nuclei, some nucleons are too far apart to attract each other by the strong force
 If the repulsion of charges is not balanced by the strong force, the nucleus will break apart.
 No atom with a mass number greater than 209 is stable.
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Mass Defect and Nuclear Stability
 Let’s look at helium-4:
2 protons (2 X 1.007276 amu) = 2.014552amu
2 neutrons (2 X 1.008665amu) = 2.017330amu
2 electrons (2 X 0.0005486 amu) = 0.001097amu
total combined mass: 4.032979amu
The actual mass of the atom is measured to be 4.00260 amu! That is 0.03038 amu less than the sum of all of its
particles. The difference between the mass of an atom and the sum of the masses of its protons, neutrons, and
electrons is called the mass defect!
 The mass defect is caused by the conversion of mass (m) to energy (E) when the nucleus was originally
formed.
Using Einstein’s equation E=mc2, we can actually calculate the energy released when a nucleus is formed from
nucleons! This is called the Nuclear Binding Energy (It can also be thought of as the amount of energy required
to break down the nucleus; therefore, the nuclear binding energy is also a measure of the stability of a nucleus.)
 Energy can be converted into mass, and mass can be turned into energy.
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Radioactivity
 The spontaneous decomposition of a nucleus to form a different nucleus accompanied by a release of energy
or a particle
 The spontaneous transformation of an unstable atomic nucleus into a stable product while emitting
radiation
Binding Energy is one indicator of nuclear stability:
Rules to Help you Predict Nuclear Stability
1. Except for Hydrogen and Helium, all stable nuclei have a number of neutrons that is equal to or greater than
the number of protons.
2. A nucleus that has an N/Z number that is too large or too small is unstable.
3. Nuclei with even numbers of neutrons and protons are more stable.
4. Nuclei that have so-called magic numbers of protons and neutrons tend to be more stable than others.
• These numbers—2, 8, 20, 28, 50, 82,and 126—apply to the number of protons or the number of neutrons
5. No atoms that have atomic numbers larger than 83 and mass numbers larger than 209 are stable.
NAME: _________________________ Pd: ________
Concept Review 3.1
Introduction to Nuclear Chemistry
1. What makes up the nucleus?
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2. What is a nucleon?
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3. What is a nuclide?
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4. Write the two ways a nuclide of Carbon can be written.
5. Describe how the strong force attracts the nucleons.
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6. What is nuclear binding energy?
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7. How is nuclear binding energy related to mass defect?
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8. Explain the relationship between the number of nucleons and the stability of nuclei.
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9. Explain why nuclear reactions occur.
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10. List the 5 rules that help you predict nuclear stability.
1. ______________________________________________________________
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2. ______________________________________________________________
3. ______________________________________________________________
4. ______________________________________________________________
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5. ______________________________________________________________
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Name: _____________________________
Ch3 Section 2
Notes Page 2
Chapter 3 Introduction to Nuclear Chemistry
“We knew the world would not be the same.”
J. Robert Oppenheimer