Nuclear Chemistry Chapter 10

10.1 Radioactivity:  Radiation A.Radioactivity: the process by which certain elements emit particular forms of radiation 1. An element that emits this radiation is called radioactive

B. Alpha radiation consists of fast-flying alpha (  ) particles 1.  particle: a combination of 2 protons and 2 neutrons- a helium nucleus! 2. Positively charged C. Beta radiation consists of fast-flying beta (  ) particles 1.  particle: an electron that is ejected by an atomic nucleus, so it is negatively charged

D. Gamma  Radiation is an extremely energetic form of electromagnetic radiation 1. It possesses a great deal of energy! 2. Carries no electrical charge or mass  Alpha particles are large in size, so they do not easily penetrate solids, but they do have a lot of kinetic energy and cause a lot of damage to soft tissue 1. Attract electrons quickly and form harmless helium

F. Beta particles move more quickly and are able to penetrate light materials and fairly deeply into skin. 1. When denser materials stop a  particle it just becomes a normal electron in the material G. Gamma Rays are the most harmful because they are pure energy- they can penetrate almost anything!

Radioactivity is a Natural Phenomenon A.Radioactivity has always been a part of the Earth and the environment 1. The energy released is used to heat water in the Earth’s interior B.The atmosphere helps block out cosmic rays

C. Radiation can affect the cells that make up your body- cells can self-repair most damage 1. Sometimes radiation damages the DNA of cells and it results in a mutation 2. Mutations may be harmless or they could lead to serious problems such as cancer or be passed on to offspring

D. Radon-222 is the leading source of naturally occurring radiation 1. Radon is found naturally in tobacco smoke and it increases smokers’ risk of lung cancer E. 1/5 th of exposure to radiation comes from non-natural sources like t.v. and medical procedures

Radioactivity Results from Imbalance of Forces in Nucleus A.Strong Nuclear Force: The force of interaction between all nucleons, effective only at VERY close distances B.Strong nuclear force and the presence of neutrons keep the protons together in the nucleus

C. SNF decrease over distance so a large nucleus is not as stable as a small one- so large ones decay by emitting high energy particles or gamma radiation

D. A large nucleus with a lot of protons there need to be many more neutrons to overcome the repulsive force E. Neutrons are unstable alone- the break down into a proton and an electron F. All atoms with a number higher than 83 are radioactive

10.2 Rates of Nuclear Decay: Shorter ½ Life= Greater Radioactivity A.Radioactive isotopes decay at different rates and is measured in terms of the half-life 1.Half-Life: time needed for half of all radioactive atoms in a material to decay 2.Ra-226 takes 1620 years B.Half-lives are not affected by external conditions

C. The time of half-life depends on the element and can range from 1 millionth of a second to 4.5 billion years

Isotopic Dating Measures the Age of a Material A.All plants contain a tiny quantity of radioactive carbon-14 and therefore all animals have a tiny amount B.When a living organism dies the percentage of carbon-14 decreases at a constant rate- its half-life 1. ½ life of C-14 is 5730 years

C. Using this knowledge about C-14 scientists are able to calculate the age of remains that contain carbon. 1. This process is called carbon-14 dating 2. There is a 15% uncertainty in carbon dating

10.3 Artificial Transmutation A.When a radioactive nucleus emits an  or  particle the atomic number is changed B.Transmutation: the changing of one element to another C.When transmutation occurs energy is released- part as  rays and most as KE

D. A  particle is an electron ejected from the nucleus when a neutron breaks down- the proton from this break-down is left which increases the atomic number by 1