Write down the things in green in your notebook!!! Nuclear Chemistry Write down the things in green in your notebook!!!

The word radioactivity was first used by Marie Curie in 1898. She used the word radioactivity to describe the property of certain substances to give off invisible “radiations” that could be detected by films.

Scientists quickly learned that there were three different kinds of radiation given off by radioactive materials. Alpha rays Beta rays Gamma rays The scientists called them “rays” because the radiation carried energy and moved in straight lines, like light rays.

We now know that radioactivity comes from the nucleus of the atom. If the nucleus has too many neutrons, or is unstable for any other reason, the atom undergoes radioactive decay. The word decay means to "break down."

**Copy down the following chart in your notes!!!** In alpha decay, the nucleus ejects two protons and two neutrons. Beta decay occurs when a neutron in the nucleus splits into a proton and an electron. Gamma decay is not truly a decay reaction in the sense that the nucleus becomes something different. **Copy down the following chart in your notes!!!**

Alpha Decay 1) The nucleus of an atom splits into two parts. 2) One of these parts (the alpha particle) goes zooming off into space. 3) The nucleus left behind has its atomic number reduced by 2 and its mass number reduced by 4 (that is, by 2 protons and 2 neutrons). There are other points, but the three above are enough for this class. Here is a typical alpha decay equation: Notice several things about it: 1) The atom on the left side is the one that splits into two pieces. 2) One of the two atoms on the right is ALWAYS an alpha particle. 3) The other atom on the right ALWAYS goes down by two in the atomic number and four in the mass number. Here's another example:

Beta Decay Beta decay is somewhat more complex than alpha decay is. These points present a simplified view of what beta decay actually is: 1) A neutron inside the nucleus of an atom breaks down, changing into a proton. 2) It emits an electron which goes zooming off into space. 3) The atomic number goes UP by one and mass number remains unchanged. Here is an example of a beta decay equation: Some points to be made about the equation: 1) The nuclide that decays is the one on the left-hand side of the equation. 2) The order of the nuclides on the right-hand side can be in any order. 3) The way it is written above is the usual way. 4) The mass number and atomic number of the antineutrino are zero and the bar above the symbol indicates it is an anti-particle. 5) The neutrino symbol is the Greek letter "nu." Here is another example of a beta decay equation:

Radioactive decay gives off energy. The energy comes from the conversion of mass into energy. Radioactivity occurs because everything in nature tends to move toward lower energy. A radioactive nucleus decays because the neutrons and protons have lower overall energy in the final nucleus than they had in the original nucleus.

Radioactive decay depends on chance. It is possible to predict the average behavior of lots of atoms, but impossible to predict when any one atom will decay. One very useful prediction we can make is the half-life. The half-life is the time it takes for one half of the atoms in any sample to decay.

Half-lives The half-life of carbon-14 is about 5,700 years. If you start out with 200 grams of C-14, 5,700 years later only 100 grams will still be C-14. The rest will have decayed to nitrogen-14.

Most radioactive materials decay in a series of reactions. Radon gas comes from the decay of uranium in the soil. Uranium (U-238) decays to radon-222 (Ra-222).

Applications of radioactivity and half lives Many satellites use radioactive decay from isotopes with long half-lives for power because energy can be produced for a long time without refueling. Isotopes with a short half-life give off lots of energy in a short time and are useful in medical imaging, but can be extremely dangerous. The isotope carbon-14 is used by archeologists to determine age.

30.1 Carbon dating Living things contain a large amount of carbon. When a living organism dies it stops exchanging carbon with the environment. As the fixed amount of carbon-14 decays, the ratio of C- 14 to C-12 slowly gets smaller with age.

Calculating with isotopes A sample of 1,000 grams of the isotope C-14 is created. The half-life of C-14 is 5,700 years. How much C-14 remains after 28,500 years? Answer: 28,500 years ÷ 5,700 = 5 half lives Half Life Equation = 1 ÷ 2n Which means for 1 gram: 1 ÷ 25 = 0.03125 grams And for 1000 grams: 1000 x 0.03125 = 31.25 grams 1) You are asked for the amount of C-14 left after 28,500 years. 2) You are given the half-life for carbon as 5,700 years. 3) One half the C-14 decay s every half-life. 4) 28,500 years is 5 times the half-life. The amount of C14 is reduced by half every 5,700 years. Start: 1,000 grams 5,700 years: 500 grams 11,400 years: 250 grams 17,100 years: 125 grams 22,800 years, 62.5 grams 28,500 years, 31.2 grams Answer = 31.2 grams

Radiation The word radiation means the flow of energy through space. There are many forms of radiation. Light, radio waves, microwaves, and x-rays are forms of electromagnetic radiation. Many people mistakenly think of radiation as only associated with nuclear reactions.

Radiation The intensity of radiation measures how much power flows per unit of area. When radiation comes from a single point, the intensity decreases inversely as the square of the distance.

Harmful radiation Radiation becomes harmful when it has enough energy to remove electrons from atoms. The process of removing an electron from an atom is called ionization. Visible light is an example of nonionizing radiation. UV light is an example of ionizing radiation.

Harmful radiation Ionizing radiation absorbed by people is measured in a unit called the rem. The total amount of radiation received by a person is called a dose, just like a dose of medicine. It is wise to limit your exposure to ionizing radiation whenever possible. Use shielding materials, such as lead, and do your work efficiently and quickly. Distance also reduces exposure.

Sources of radiation Ionizing radiation is a natural part of our environment. There are two chief sources of radiation you will probably be exposed to: background radiation. radiation from medical procedures such as x-rays. Background radiation results in an average dose of 0.3 rem per year for someone living in the United States.

Background radiation Background radiation levels can vary widely from place to place. Cosmic rays are high energy particles that come from outside our solar system. Radioactive material from nuclear weapons is called fallout. Radioactive radon gas is present in basements and the atmosphere.

X-ray machines X-rays are photons, like visible light photons only with much more energy. Diagnostic x-rays are used to produce images of bones and teeth on x-ray film. Xray film turns black when exposed to x-rays.

X-ray machines Therapeutic x-rays are used to destroy diseased tissue, such as cancer cells. Low levels of x-rays do not destroy cells, but high levels do. The beams are made to overlap at the place where the doctor wants to destroy diseased cells.

Nuclear Reactions and Energy A nuclear reaction is any process that changes the nucleus of an atom. Radioactive decay is one form of nuclear reaction.

Nuclear Reactions and Energy If you could take apart a nucleus and separate all of its protons and neutrons, the separated protons and neutrons would have more mass than the nucleus did. The mass of a nucleus is reduced by the energy that is released when the nucleus comes together. Nuclear reactions can convert mass into energy.

Nuclear Reactions and Energy When separate protons and neutrons come together in a nucleus, energy is released. The more energy that is released, the lower the energy of the final nucleus. The energy of the nucleus depends on the mass and atomic number.

Fusion reactions 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.

Fission reactions 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.