Essay on chapter 21 nuclear chemistry

Submitted By maryann97
Words: 1480
Pages: 6

21.1 Radioactivity [p.894]
1. Background information
a. Nuclear Chemistry- study of nuclear reactions.
b. nucleons– protons and neutrons
c. mass numbers determine the isotope of an element
d. Stability of a nucleus is dependent on the proton to neutron ration.
e. Nuclide is a nucleus with a specific number of protons and neutrons
i. Radionuclides- nuclei that are radioactive
1. Unstable and spontaneously decay emitting particles and electromagnetic radiation
2. Emissions help unstable isotopes become more stable ii. Radioisotopes – atoms containing these nuclei
2. Nuclear Equations
a. Alpha decay (alpha emission)= helium nucleus
b. Radioactive decay = spontaneous decomposition of nuclei
i. Example ii. Note the sum of the mass numbers and atomic numbers for the products and reactants must be equal.
c. Radioactive properties of a nucleus is independent of the chemical state of the atom
3. Types of Radioactive Decay
a. Alpha
i. Symbol or ii. Stream of helium-4 nuclei iii. 2+ charge iv. Relative penetrating power of 1
b. Beta
i. High speed electrons emitted from unstable nuclei ii. Symbol or iii. 1- charge iv. Relative penetrating power of 100
v. Beta emission is = to the conversion of a neutron to a proton
c. Gamma
i. High energy photons ii. Does not change the value of the mass number or the atomic number iii. Symbol or iv. 0 charge
v. Relative penetrating power of 10000 vi. Usually accompany other transmissions vii. Generally not shown in nuclear equations
d. Positron
i. Has same mass and opposite charge of electron ii. Symbol iii. 1+ charge iv. Positron emission converts a proton to a neutron
e. Electron Capture
i. Capture of an electron by the nucleus ii. Symbol or iii. 1- charge iv. Appears on the reactant side
21.2 Patterns of Nuclear Stability [p.898]
1. Neutron-to-Proton Ratio
a. Nuclear force or strong force holds the nucleons hold together
i. Necessary because protons in nucleus repel ii. Neutrons play a role in establishing the strong force iii. The greater the number of protons, the greater the number of neutrons needed for stability iv. Belt of stability ends at bismuth
v. All nuclei with 84 or more protons are radioactive
b. Type of reaction depends largely on neutron: proton
i. Nuclei above the belt of stability tend to emit beta particles to reducing the number of neutrons and increasing the number of protons to get closer to the 1:1 ii. Nuclei below the belt of stability (low n:p ) tend increase radios through positron emission or electron capture. Positron more common, but electron capture more common in large nuclear charge atoms iii. Nuclei with atomic numbers > 84 tend to undergo alpha emssions
2. Radioactive series( Nuclear disintegration series)- series of nuclear reactions that end in stability
3. Further Observations
a. Magic Numbers-the number of protons and neutrons that are generally more stable
i. 2,8,20,28,50, 82 protons ii. 2,8, 20, 28, 50, 82 and 126 neutrons
b. Nuclei with even numbers of protons and neutrons tend be more stable
21.3 Nuclear Transmutations [p. 901]
1. Background
a. Nuclear reactions caused by a nucleus being struck by a neutron or another nucleus
b. Rutherford performed the 1st conversion of a nucleus
c. Transmutations usually written in the following order
i. Target nucleus ii. Bombarding particle iii. Ejected particle iv. Product nucleus
d. Accelerating Charged particles
i. Charged particles must be moving fast to overcome the repulsive force of the target nucleus ii. Particle accelerators called “atom smashers” , cyclotrons , and synchrotrons are used accelerate the alpha particles
e. Using Neutrons
i. Not repelled by nucleus so acceleration is not needed ii. Used in the development of most synthetic isotopes used in medicine and scientific research
f. Transuranium Elements
i. Elements with an atomic number above 92 ii. Short lived nuclei
21.4 Rates of Radioactive Decay [p.903]
1. General information
a. Radioactive decay- 1st order kinetic process