Ch 21: Nuclear Chemistry

Radioactivity Wilhelm Roentgen made a big discovery in He found that invisible rays were emitted when electrons bombarded materials. He named these rays, X-rays. At the same time, Henri Becquerel was studying minerals that emitted light after being exposed to sunlight, a phenomenon called phosphorescence.

Radioactivity Marie Curie and her husband Pierre were working with Becquerel and took his mineral sample and were able to isolate the components emitting the rays. Marie named the process by which materials give off such rays Radioactivity. Radiation: the penetrating rays and particles emitted by a radioactive source.

Radioactivity Marie Curie was the first woman to win the Nobel Prize and is the only person to receive Nobel Prizes in two different sciences--physics and chemistry!

Nuclear Reactions vs. Normal Chemical Changes Marie Curie discovered that: Chemical Reactions were affected by Pressure and Temperature, while Nuclear Reactions are not. Nuclear Reactions involve the nucleus, which changes the type of element. Chemical reactions involve electrons, not protons and neutrons.

When a substance emits radiation, it changes its identity. A radioactive element has an unstable nucleus. Isotopes are atoms of the same element that have different numbers of neutrons and mass number. Radioisotopes: isotopes of atoms with unstable nuclei

Nuclear Stability and Decay Nuclear Force: the attractive force that acts between all nuclear particles that are extremely close together, such as neutrons and protons in a nucleus. Band of Stability: the location of stable nuclei on a neutron vs. proton plot.

The neutron-to-proton ratio determines the type of decay that occurs. The four types of decay are: beta emission electron capture positron emission alpha emission.

Types of Radiation The three types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation. They can be separated by an electric field, as shown below.

Alpha Radiation Alpha Particle: a positively charged helium isotope. Can be written with either symbol,  or It contains 2 protons and 2 neutrons and has a 2+ charge Po Pb He

Beta Radiation Beta Particle: a very fast moving electron. Electron resulting from the breaking apart of a neutron in an atom. 146 C N e

Positron Emission Positron: a particle with the same mass as an electron, but has positive charge. Emitted from the nucleus during some kinds of radioactive decay O N β

Gamma Radiation Gamma Rays: high energy electromagnetic radiation. The emission of gamma rays does not change the atomic number or mass number of a nucleus. Used to destroy tumors Po Po γ

Penetrating Abilities Alpha: stopped by piece of paper. Beta: stopped by thin metal Gamma: stopped by thick lead and concrete.

Half-Life Half-life: the time required for one-half of the nuclei of a radioisotope sample to decay to products. After each half-life, half of the existing radioactive atoms have decayed into atoms of a new element.

Half-Life Calculation Carbon-14 emits beta radiation and decays with a half-life of 5730 years. Assume you start with a mass of 2.00 x g of Carbon-14. a.How long is three half-lives? 3 x 5730 years = 17,190 years b.How many grams of the isotope remain at the end of three half-lives? 2.00 x g x 1/2 x 1/2 x 1/2 = x g