Nuclear Chemistry

Chemical Reactions Nuclear Reactions No new elements can be produced. Only the electrons participate. Relatively small amounts of energy are released or absorbed. Rate of reaction depends on factors such as concentration, temperature, catalyst, and pressure Nuclear Reactions Elements may be converted from one to another (transmutation) Particles within the nucleus are involved. Tremendous amounts of energy are released or absorbed. Rate of reaction in not influenced by external factors.

Radioactive Decay Radioactivity: The process of emitting particles or energy from the nucleus of an unstable isotope (radioisotope) to become stable. Radioactive Decay: The spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by radiation. Radiation: The particles or energy emitted from the nucleus. (a, b, g)

Types of Radioactive Decay Particle Mass (amu) Charge Penetration/ Shielding alpha (α) or 4.0026 (4) 2+ low (paper) beta (β) 0.00055 (0) 1- moderate (metal foil, 0.3 cm) positron 1+ proton 1.0073 (1) neutron 1.0087 (1) High gamma Very high (5cm lead or 1m concrete)

Nuclear Band of Stability Stability of the nucleus can be correlated to neutron/proton ratio (n/p) -for isotopes of low atomic number (1-20), the stability ratio is 1:1 -for the heavier isotopes, the ratio increases to 1.5:1 above the band – unstable, many neutrons. Undergo beta decay nuclei with 82 or more protons often decay by alpha emission

Nuclear Reactions The mass number must be equal on both sides. The atomic number must be equal on both sides.

Neutron Rich Nuclei (Above the band of Stability) Beta emission A beta particle is an electron ejected from the nucleus when a neutron is converted into a proton.

Neutron-Poor Nuclei (Below the band of stability) Positron Emission – positrons are emitted when protons are converted to neutrons. lighter elements

Neutron-Poor Nuclei Cont. Electron Capture – first energy electron captured by nucleus converting a proton to a neutron.

Neutron-Poor Nuclei (Below the band of Stability) Alpha Emission – Some of the neutron-poor nuclei, especially heavier ones, increase their neutron-to-proton ratios emitting alpha particles.

Half-Life Half-life is the amount of time it takes for half of a radioisotope’s nuclei to decay into its products. Examples. a. Sr-90 has a half-life of 28.79 years. How much of a 100.0 g sample of Sr-90 is left after 5 half-lives? b. If 3 half-lives passes, and 450 mg of Sr-90 remains, how much was originally present?

Half-Life N = amount of radioisotope remaining N0 = initial amount of radioisotope n = number of half-lives passed t = total time passed T = length of half-life     Example. Cs-137 has a half-life of 30.17 days. How much of a 10.0 g sample of Cs-137 remains after 250 days?

Nuclear Fission Heavier nuclei are unstable. To become more stable they can split into smaller, more stable nuclei. This is called nuclear fission and it is accompanied by a large release of energy. Example: Example: 235U + 1n  144Ba + 90Zr + 2 1n

Nuclear Fusion Example: 3He + 4He  7Be + g When two small unstable nuclei join to form a larger stable isotope, this is called nuclear fusion. This is the process that occurs in the sun. Example: 3He + 4He  7Be + g Example: