Nuclear Chemistry Basic Concepts

Basic Concepts What part of an atom is involved in chemical reactions? Valence electrons. What is the difference between chemical reactions and nuclear reactions? Chemical reactions: the nucleus remains unchanged, involves the transfer or sharing of valence electrons. Nuclear reactions involve changes in the nuclei of atoms.

Radioactivity Nuclear reactions are those in which the nuclei of unstable isotopes, called radioisotopes, gain stability by undergoing changes. Unlike chemical reactions, nuclear reactions are not affected by changes in temperature, pressure or the presence of catalysts.

What types of radiation exist? The three most common types of radiation emitted by unstable nuclei are Alpha  Beta  Gamma  Gamma rays are particularly harmful because they penetrate body tissues.

Alpha decay Symbol is a or is written as . An alpha particle is a helium nucleus - two protons and two neutrons. It therefore has considerable mass compared to a beta particle or gamma ray. Atomic number decreases by 2, mass number decreases by 4. Stopped by a sheet of paper.

Beta decay Symbol is b or is written as . A beta particle is an electron therefore it has negligible mass. It is emitted from the nucleus along with a neutrino. In the process, a neutron becomes a proton. Atomic number increases by one, mass number is unchanged. It can be stopped by 6 mm of aluminum foil.

Gamma decay Symbol is g. Gamma rays have no mass and no electrical charge. Gamma radiation is electromagnetic radiation. It is like visible light, but much more energetic and has high penetrating power. Mass number and atomic number do not change. Stopped incompletely by several feet of concrete or lead.

Transmutation The conversion of an atom of one element to an atom of another element is called transmutation. Radioactive decay is one way in which transmutation occurs. Transmutation can also occur when high energy particles bombard the nucleus of an atom. The high-energy particles may be protons, neutrons or alpha particles.

Rutherford’s Artificial Transmutation Ernest Rutherford carried out the first artificial transmutation when he bombarded nitrogen gas with alpha particles. What particles were formed? This initial reaction was unstable and quickly decomposed to a stable isotope of oxygen. What was the other particle?

Artificial Transmutation proton

Half-Life of a Radioisotope The time for the radiation level to fall (decay) to one-half its initial value decay curve 8 mg 4 mg 2 mg 1 mg initial 1 half-life 2 3

Half-Life Every radioisotope decays at a characteristic rate A half-life is the time required for one-half of the nuclei in a radioisotope to decay.

Examples of Half-Life Isotope Half life C-15 2.4 sec Ra-224 3.6 days I-125 60 days C-14 5700 years U-235 710 000 000 years

Learning Check The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 26 hours?

Solution t1/2 = 13 hrs 26 hours = 2 x t1/2 Amount initial = 64mg Amount remaining = 64 mg x ½ x ½ = 16 mg

Nuclear Fission Nuclear fission occurs when fissionable isotopes are bombarded with neutrons. As the isotopes split, they release more neutrons, which split more nuclei in a chain reaction.

Nuclear Fission Fission large nuclei break up 235U + 1n 139Ba + 94Kr + 3 1n + 92 0 56 36 0 Energy

Fission Nuclear power plants use neutron moderation and neutron absorption to control the fission reaction used to produce electricity.

Nuclear Fusion In nuclear fusion, small nuclei fuse to make heavier nuclei. The sun’s energy is released when hydrogen nuclei fuse to make helium. This occurs in other stars too. Energy

Learning Check Indicate if each of the following are Fission (2) fusion Nucleus splits Large amounts of energy released Small nuclei form larger nuclei Hydrogen nuclei react Energy

Solution Indicate if each of the following are Fission (2) fusion 1 Nucleus splits 1 + 2 Large amounts of energy released 2 Small nuclei form larger nuclei 2 Hydrogen nuclei react

Write nuclear equations for these conversions:

Complete these nuclear equations

Solution