Nuclear Chemistry CHEM 396 by Dr. Ahmad Hamaed Fall 2015

Has a role in shaping world politics. Nuclear Chemistry Nuclear chemistry, by definition, is the study of the structure of atomic nuclei and the changes they undergo. Why it is important? Has a role in shaping world politics. Due to its applications in the production of electricity and in the diagnosis and treatment of diseases. Therefore, nuclear chemistry has profound effects upon the world in which we live.

Discovery of Radioactivity (1895-1898)

Matter and Energy Nuclear science began with Albert Einstein at the beginning of the last century, who recognized that matter and energy were equivalent; E = mc2. Energy which is defined as the capacity to do work or to provide heat, had an equivalency with matter- the mass of the physical universe. If matter could be converted to energy in a practical manner, a very small amount of matter would generate enormous amounts of energy.

Definitions Quantum: The smallest discrete amount of any quantity (plural: quanta). Nucleus: A collection of protons and neutrons that forms the core of an atom (plural: nuclei). Nucleons: Subatomic particles in the nucleus, e.g., protons and neutrons. Radio nucleotides: Radioactive nuclei; unstable nuclei that spontaneously emit particles and electromagnetic radiation.

Definitions Fermion: Any particle that has odd-half-integer (1/2, 3/2, …) intrinsic angular momentum (spin). All particles are either fermions or bosons. Bosons are particles with integer spin. Fermion obey the Pauli Exclusion Principle, which states that no two fermions can exist in the same state at the same time. Pauli Exclusion Principle: The principle that no two particles in the same quantum state may exist in the same place at the same time. Particles that obey this principle are called fermions; particles that do not obey the Pauli Exclusion Principle are called bosons.

Definitions Electrons, protons, and neutrons are all fermions. Different isotopes of the same elements are distinguished by having different numbers of neutrons in their nucleus. Proton: The most common hadron, a baryon with electric charge +1 equal and opposite to that of the electron. Protons have a basic structure of two up quarks and one down quark. The nucleus of a hydrogen atom is a proton. A nucleus with electric charge Z contains Z protons.

Definitions Quark: Nuclei which is a fundamental fermion that has strong interactions. Quarks have electric charge of either +2/3 (up, top) or -1/3 (down, bottom) in units where the proton charge is 1. Meson: A hadron made of an even number of quark-antiquark constituents. The basic structure of most meson is one quark and one antiquark. Neutron: A baryon with electric charge zero; it is a fermion with a basic structure of two down quarks and one up quark (held together by gluons).

Definitions Electron: The least massive electrically-charged particle, having absolutely stable. It is the most common lepton, with electric charge -1. Alpha particle: A positively charged helium isotope. Beta particle: High speed electron Positron: high energy photon (+ve charge), it is an antiparticle of an electron (e+). Gamma rays: high energy photon (zero charge).

A Comparison of Chemical and Nuclear Reactions Characteristics of Chemical and Nuclear Reactions Chemical Reactions Nuclear Reactions 1- Occurs when bonds are broken and formed. 1- Occurs when nuclei emits particles and/ or rays 2- Atoms remain unchanged, though they may be rearranged. 2- Atoms are often converted into atoms of another element. 3- Involve only valence electrons. 3- May involve protons, neutrons, and electrons. 4- Associated with small energy changes. 4- Associated with large energy changes. 5- Reaction rate is influenced by temperature, pressure, concentration, and catalysts. 5- Reaction rate is not normally affected by temperature, pressure, concentration, and catalysts.

Nuclear Reactions vs. Normal Chemical Changes Nuclear reactions involve the nucleus The nucleus opens, and protons and neutrons are rearranged The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called binding energy. “Normal” Chemical Reactions involve electrons, not protons and neutrons

The Discovery of Radioactivity In 1895, Wilhelm Roentgen (1845-1923) found that invisible rays were emitted when electrons bombarded the surface of certain materials. The emitted rays caused the photographic plates to darken. Roentgen named these invisible high-energy emissions X-rays. Henry Becquerel (1859-1906) studied minerals that emit light after being exposed to sunlight, a phenomenon called phosphorescence. Becquerel accidently discovered that phosphorescent uranium salts-even when not exposed to light-produced spontaneous emissions that darkened photographic plates.

The Discovery of Radioactivity Marie Curie (1867-1934) and her husband Pierre (1859- 1906) took Becquerel’s mineral sample and isolated the components emitting the rays. They concluded that the uranium atoms present in the mineral are the source of the radiations. Marie curie named the process by which materials give off such rays radioactivity; the rays and particles emitted by a radioactive source are called radiation.

Isotopes/ Radio-isotopes Recall that Isotopes are atoms of the same element that have different numbers of neutrons. Isotopes of atoms with unstable nuclei are called Radioisotopes. These unstable nuclei emit radiation to attain a more stable atomic configurations in a process called radioactive decay. During radioactive decay, unstable atoms lose energy by emitting one of several types of radiation.

What are the types of radiation emitted by a radioactive sources? Alpha (ά) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons Beta (β) – an electron Gamma (γ) – pure energy; called a ray rather than a particle

Types of Radiation

Review of the Structure of the Atom

Other Nuclear Particles Neutron Positron – a positive electron Proton – usually referred to as hydrogen-1 Any other elemental isotope

Nuclear Stability

Nuclear Stability: Band of Stability

Neutron to Proton Ration for Group 15 Elements

Properties of Alpha, Beta, and Gamma Radiation Composition Alpha particles Beta particles High-energy electromagnetic radiation Description of radiation Helium nuclei Electron Photon Charge +2 -1 Mass 6.64 x10-24 kG 9.11 x10-28kG Approximate energy 5 MeV 0.05 to 1 MeV 1MeV Relative penetrating power Blocked by paper Blocked by metal foil Not completely blocked by lead or concrete

The Effect of an Electric Field on the Three Types of Radiation

Alpha Decay A radium-226 nucleus undergoes an alpha decay to form Radon-222. What is the charge on the alpha particle? What particle is formed when Polonium-210 undergoes alpha decay?

Types of Radioactive Decay: Alpha Decay

Types of Radioactive Decay: Beta Decay

Types of Radioactive Decay: Gamma Rays

Summary of Radioactive Decay Processes

Nuclear Transmutation

Half-life

Half-life

Half-life

Half-life

What Does Half-life mean?