1. Learning Targets I can name the force that holds the atom’s nucleus together I can describe the two reasons why some isotopes are radioactive. I can describe the four types of radiation I can predict the type of decay an element will go through to become stable.

2. Nuclear Reactions Nuclear Reactions involve the nucleus and may change one element into another Two types: – Decay reactions- nucleus spontaneously breaks up – Bombardment reactions- a nucleus is struck by another nucleus or some nuclear particle, such as a neutron or proton Radiation- transmission of energy through space – Nuclear reactions involve much more energy than chemical reactions.

3. Radioactive Elements Elements with an unstable nucleus will spontaneously lose particles or energy to become stable. Two reasons for instability: – Nucleus is too large (atomic # > 83) The nucleus is held together with the STRONG FORCE, which at short distances is stronger than the electromagnetic force that would cause protons to repel At longer distances (larger nucleus) the electromagnetic force takes over and the nucleus begins to fall apart. – Imbalance between protons and neutrons In smaller elements a 1:1 ratio is stable In larger elements more neutrons are required to hold the nucleus together

4. Radioactive Isotopes All elements with an atomic number over 83 are radioactive Many other smaller elements have radioactive isotopes. (Carbon-14) In graph (at right), dotted line shows the “Belt of Stability”. A: B: C:

5. Types of Radioactive Decay Alpha radiation – A helium nucleus (2 protons and 2 neutrons) are ejected Beta radiation – A neutron becomes a proton, and an electron is ejected The nucleus changes! The atomic number is decreased by 2! The atomic number increases by 1!

6. Types of Radiation Positron emission – a proton is converted to a neutron and a positron (e + ) is emitted Gamma radiation – The nucleus does not change, but energy is released

7. Learning Check What is the name of the force that holds protons together in the nucleus? What are the two reasons that an element could be radioactive? What happens to the nucleus during – alpha decay? – beta decay? – positron emission? – gamma decay? Predict the type of decay for each element: – Uranium- 235 – Lithium-8 – Oxygen-15