Nuclear Chemistry 7.5

The Discovery of Radiation Wilhelm Roentgen – Discovered X rays in 1895.

The Discovery of Radiation Henri Becquerrel – accidently discovered radioacitivity in 1896 when he left a uranium salt in a desk drawer on a photographic plate. He hypothesized that the salt was g giving off some type of energy.

Marie and Pierre Curie – studied radioactivity in the late 1800s and early 1900s. Radiation poisoning took Marie Curies life. She won the Nobel Prize in 1903 (They were super excited about it!)

Introduction to Nuclear Chemistry The Nucleus – the protons and neutrons in the center of the atom that make up the positive charge. Positive protons should repel from one another, why do they stay together in the nucleus? The Strong Force – the force in the nucleus that causes protons and neutrons to attract to one another.

Typically in large or unstable nuclei the repulsion of the positive protons overcomes the strong force and nuclei decay.

Radioactivity Radioactivity – The process of nuclear decay Decay depends on nuclear stability. If an isotope of an atom is radioactive it is called a radioisotope.

mass # atomic # Chemical Symbols C A chemical symbol looks like… To find the number of neutrons , subtract the atomic number from the mass number. mass # 14 C atomic # 6

Common Radioisotopes

Types of Radioactivity Alpha particle – a particle of two protons and two neutrons that comes from a radioisotope. Often referred to as a Helium Nucleus. Beta Particle – an electron emmitted from the nucleus of a radioisotope. Gamma Rays – a form of radiation that is a powerful electromagnetic wave

Measuring Radiation Geiger Counter – a device that measures radioactivity by producing an electric current when radiation is present.

Half-Life Half life is the time required for half of a radioisotope’s nuclei to decay into its products. For any radioisotope, # of ½ lives % Remaining 100% 1 50% 2 25% 3 12.5% 4 6.25% 5 3.125% 6 1.5625%

Half-Life For example, suppose you have 10.0 grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years?   You can use a table: # of ½ lives Time (Years) Amount Remaining (g) 10 1 29 5 2 58 2.5 3 87 1.25 4 116 0.625

Half-Life

Nuclear Fusion and Nuclear Fission A fusion reaction is a nuclear reaction that combines, or fuses, two smaller nuclei into a larger nucleus. It is difficult to make fusion reactions occur because positively charged nuclei repel each other. All stars, including the sun, generate energy through fusion.

Nuclear Fusion and Nuclear Fission A fission reaction splits up a large nucleus into smaller pieces. A fission reaction typically happens when a neutron hits a nucleus with enough energy to make the nucleus unstable. Examples-atomic bomb

Uses of Radiation Radioactive dating - Carbon - 14 used to determine the age of an object that was once alive. Radiation to target cancer cells X-rays Medical tests using radioactive dyes, called tracers Sterilizing equipment using radioactive rays Smoke Detectors – alpha decay of americium 241

Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes