Nuclear Chemistry Notes & Summary PDF

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Nuclear Chemistry Notes & Summary...

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Nuclear Chemistry Notes & Summary

Nuclear Radiation The Discovery of Radiation: Nuclear chemistry is concerned with the structure of atomic nuclei and the changes they undergo. Nuclear reactions are different from other types of reactions. Marie Curie and her husband Pierre isolated the first radioactive materials.

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Comparison of Chemical and Nuclear Reactions Chemical Reactions • • • •

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Occur when bonds are broken and formed Involve only valence electrons Associated with small energy changes Atoms keep the same identity although they might gain, lose, or share electrons, and form new substances Temperature, pressure, concentration, and catalysts affect reaction rates

Nuclear Reactions     

Occur when nuclei combine, split, and emit radiation Can involve protons, neutrons, and electrons Associated with large energy changes Atoms of one element are often converted into atoms of another element Temperature, pressure, and catalysts do not normally affect reaction rates

Types of Radiation   

Isotopes of atoms with unstable nuclei are called radioisotopes. Unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay. The three most common types of radiation are alpha, beta, and gamma.

Properties of alpha, beta, and gamma radiations. Alpha Radiation:

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Alpha particles have the same composition as a helium nucleus—two protons and two neutrons. Because of the protons, alpha particles have a 2+ charge. Alpha radiation consists of a stream of particles. Alpha radiation is not very penetrating—a single sheet of paper will stop an alpha particle.

Beta Radiation:   

Beta particles are very fast-moving electrons emitted when a neutron is converted to a proton. Beta particles have insignificant mass and a 1– charge. Beta radiation is a stream of fast-moving particles with greater penetrating power—a thin sheet of foil will stop them.

Gama Rays:      

Gamma rays are high-energy electromagnetic radiation. Gamma rays have no mass or charge. Gamma rays almost always accompany alpha and beta radiation. X rays are a form of high-energy electromagnetic radiation emitted from certain materials in an excited state. The ability of radiation to pass through matter is called its penetrating power. Gamma rays are highly penetrating because they have no charge and no mass.

Radioactive Decay

Nuclear Stability: 

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Except for gamma radiation, radioactive decay involves transmutation, or the conversion of an element into another element. Protons and neutrons are referred to as nucleons. All nucleons remain in the dense nucleus because of the strong nuclear force. The strong nuclear force acts on subatomic particles that are extremely close together and overcomes the electrostatic repulsion among protons. As atomic number increases, more and more neutrons are needed to produce a strong nuclear force that is sufficient to balance the electrostatic repulsion between protons. Neutron to proton ratio increases gradually to about 1.5:1. The area on the graph within which all stable nuclei are found is known as the band of stability. All radioactive nuclei are found outside the band. The band ends at Pb-208; all elements with atomic numbers greater than 82 are radioactive.

Types of Radioactive Decay:

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Atoms can undergo different types of decay—beta decay, alpha decay, positron emission, or electron captures—to gain stability.

Beta Decay:  

In beta decay, radioisotopes above the band of stability have too many neutrons to be stable. Beta decay decreases the number of neutrons in the nucleus by converting one to a proton and emitting a beta particle.

Alpha Decay:        

In alpha decay, nuclei with more than 82 protons are radioactive and decay spontaneously. Both neutrons and protons must be reduced. Emitting alpha particles reduces both neutrons and protons. Nuclei with low neutron to proton ratios have two common decay processes. A positron is a particle with the same mass as an electron but opposite charge. Positron emission is a radioactive decay process that involves the emission of a positron from the nucleus. During positron emission, a proton in the nucleus is converted to a neutron and a positron, and the positron is then emitted. Electron capture occurs when the nucleus of an atom draws in a surrounding electron and combines with a proton to form a neutron.

Writing and Balancing Nuclear Equations:   

Nuclear reactions are expressed by balanced nuclear equations. In balanced nuclear equations, mass numbers and charges are conserved. Example: A plutonium-238 atom undergoes alpha decay, write a balanced equation for this decay.

Radioactive Series: 

A series of nuclear reactions that begins with an unstable nucleus and results in the formation of a stable nucleus is called a radioactive decay series.

Radioactive Decay Rates:    

Radioactive decay rates are measured in half-lives. A half-life is the time required for one-half of a radioisotope to decay into its products. The process of determining the age of an object by measuring the amount of certain isotopes is called radiochemical dating. Carbon-dating is used to measure the age of artifacts that were once part of a living organism.

N is the remaining amount. N0 is the initial amount. n is the number of half-lives that have passed. t is the elapsed time and T is the duration of the half-life.

Unstable Nuclei and Radioactive Decay Radioactivity:       

Nuclear reactions can change one element into another element. In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity. The rays and particles emitted are called radiation. A reaction that involves a change in an atom's nucleus is called a nuclear reaction. Unstable nuclei lose energy by emitting radiation in a spontaneous process called radioactive decay. Unstable radioactive elements undergo radioactive decay thus forming stable nonradioactive elements. There are three types of radiation: alpha, beta, and gamma

Alpha Radiation   

Alpha radiation is made up of positively charged particles called alpha particles. Each alpha particle contains two protons and two neutrons and has a 2+ charge. The figure shown below is a nuclear equation showing the radioactive decay of radium226 to radon-222.

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An alpha equivalent to a helium-4 nucleus and is represented by He or α. Thus, showing mass is conserved in a nuclear equation.

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particle is

Beta Radiation  

Beta radiation is radiation that has a negative charge and emits beta particles. Each beta particle is an electron with a 1– charge.

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During Beta decay, a neutron is converted to a proton and an electron. The electron is emitted and the proton stays in the nucleus.

Radiation Deflection:

Types of Radiation: Gamma Radiation  

Gamma rays are high-energy radiation with no mass and are neutral. They usually accompany alpha and beta radiation.

Gamma rays

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account for most of the energy lost during radioactive decay. Because gamma rays are massless, the emission of gamma rays by themselves cannot result in the formation of a new atom.

Characteristics of Radiation:

Nuclear Stability: 

Atoms that contain too many or two few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus.

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Few exist in nature—most have already decayed to stable forms....