Radioactivity and Nuclear Reactions Chapter 18 in the Glencoe Textbook

What do you remember about atoms? The nucleus contains _________& _________. Most of the volume of the atom is _______________. Most the mass of the atom is located in the __________. Draw a picture of a helium atom. (Sugar grain-10m atom analogy)

The Nucleus What keeps the __ protons and the ______ neutrons together in the nucleus? The electric force between particles make them ________ each other. The _________ force makes them attract each other. _______ times stronger than the electric force Only works over very _________ distances

The Nucleus

The Nucleus’ Forces All nuclei have repulsion due to _______ force and attraction due to __________ force. Small nuclei have few protons ___________ each other, so the strong force is much ______________ than the total electric force. Large nuclei have many protons creating a large total ___________ force of repulsion. The strong nuclear force is less because the distance is ____________ in the large nucleus.

Radioactivity When the strong nuclear force is able to keep the nucleus together, the atom is _________. When the electric force of repulsion is _______ than the strong nuclear force, the atom decays giving off ________ & _____. Called radioactivity

Radioactivity So which atoms would you expect to be radioactive? All with atomic number above 83 Atomic number above 92 are so unstable that they don’t exist in nature! Some small nuclei can also be radioactive, and isotopes can be stable or unstable. What do you remember about isotopes?

Radioactive Isotopes When the number of protons and neutrons are almost _________ in smaller atoms, the nucleus is stable. In heavier stable atoms, the ratio of neutrons to protons is about 3:2. When the nucleus has too ______ or too _____ neutrons compared to the # of protons, the atom is unstable/radioactive.

How to write nuclear symbols Mass number Symbol Atomic number Examples: C-12

How was this discovered? 1896, Henri Becquerel left U salt in a desk drawer with a photographic plate U salt darkened the plate He thought invisible rays/radiation had darkened the plate. 1898 Marie & Pierre Curie discovered radioactive elements Po & Ra

Nuclear Decay When an unstable nucleus decays, particles and energy called nuclear _______________ are emitted from it. Three types of nuclear radiation are Alpha Beta Gamma (Named for the first 3 Greek letters of the alphabet)

3 types of radiation ALPHA BETA GAMMA Made of Symbol Charge Mass Relative E Relative penetration Stopped by

SHIELDING from radiation

Transmutation Unstable atoms decay until a stable atom forms. When alpha and beta radiation are released, the identity of the atom changes. Called transmutation Only happens in nuclear rxns, not ordinary chem rxns Use the symbols for the type of radiation to determine the ID of the new element

Transmutation Alpha decay One product must be a He nucleus Website animation Example: U-238 Example: Po-210

Transmutation Beta decay One product must be an electron 0-1e Website animation Example: C-14 Example: I-131

Transmutation Gamma radiation DOES NOT CAUSE TRANSMUTATION Usually accompanies alpha and beta decay Website animation

Half-Life Unstable atoms decay at different rates. Some take seconds and some take billions of years The time required for half of the atoms in a radioactive sample to decay is called the half-life of the isotope. (Stand/radioactive-sit/stable activity) Link to half- life website See activboard program for ½ life problems Half-life experiment

Radioactive Dating What did you learn from the website?