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Chapter 20 Nuclear Reactions  

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Differ from ordinary reactions Radioactivity o The spontaneous emission of particles o The radiation from unstable nuclei o All elements with an atomic number greater than 83 are radioactive and unstable Nuclear Transmutation o Conversation of one nucleus to another o Results from the attack of nuclei by neutrons, protons or other nuclei. o Happens as a result of a collision between two particles

Chemical Reactions

Nuclear Reactions

1 Atoms are rearranged by the breaking and . forming of chemical bonds.

1. Elements are converted to other elements (or isotopes).

2 Only electrons in atomic or molecular orbitals are 2. Protons, neutrons, electrons, and other subatomic particles such as α particles may be involved. . involved in the reaction. 3 Reactions are accompanied by the absorption or . release of relatively small amounts of energy.

3. Reactions are accompanied by the absorption or release of tremendous amounts of energy.

4 Rates of reaction are influenced by temperature, . pressure, concentration, and catalysts.

4. Rates of reaction normally are not affected by temperature, pressure, or catalysts.

Balancing Nuclear Equations 

We must also explicitly indicate the number of subatomic particles in every species involved in the reaction. o Mass number is at top o Atomic number is at bottom

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Positron o Subatomic particle with the same mass as an electron, but with a positive charge.

Nuclear Stability 

Determined by the difference between coulombic repulsion and the short-range attraction. o If repulsion outweighs attraction, the nucleus disintegrates, emitting particles and/or radiation. o If attractive forces prevail, the nucleus is stable.

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Belt of Stability o Most radioactive nuclei lie outside this belt

Nuclear Binding Energy 

The energy required to break up a nucleus into its components protons and neutrons.

 o

Makes it possible to compare the stability of all nuclei

Mass Defect 

The difference between the actual mass of a nucleus and the mass calculated by summing the masses of the individual nucleons o The loss in mass shows up as energy (heat) given off to the surroundings (exothermic) 

C is the speed of light

Radioactivity  

spontaneous emission by unstable nuclei of particles or electromagnetic radiation, or both, is known as radioactivity Types of radioactivity o Emission of alpha particles  Doubly charged helium nuclei, He2+ o Emission of beta particles  electrons of nuclear origin o Emission of γ rays o Emission of positrons o Electron capture

Radioactive Decay Series    

A sequence of nuclear reactions that ultimately result in the formation of a stable isotope. Balancing is very important Parent o Beginning radioactive isotope Daughter

o

Product isotope

Kinetics of Radioactive Decay    

Radioactive decays obey first order kinetics...