Chapter 9 pages 258-287 And Chapter 18 pages 550-553 Unit 7 Radioactivity Chapter 9 pages 258-287 And Chapter 18 pages 550-553

Structure of the Atom Protons, neutrons, electrons Quarks- small particles that make up protons and neutrons

Using the periodic table Atomic # = # of protons The lesser of the two numbers in the element box On periodic table, the # of protons = # of electrons

Atomic mass = the # of protons + # of neutrons The greater of the two numbers in the element box To find the # of neutrons: Atomic mass – atomic #

What is the atomic number of zinc? How many electrons does tungsten have? How many neutrons does scandium have? What is the atomic mass of carbon? How many protons does astatine have?

Isotopes Same number of protons (it is the same element) Therefore it has the same atomic # Different number of neutrons Therefore, it has a different atomic mass

Periodic Table Structure Periods: Go left to right Increasing # of protons and electrons Groups: Go up and down Have similar reactive properties

The Nucleus Proton and neutrons are found in the nucleus Outside of the nucleus are the electrons The size of the nucleus in an atom can be compared to a marble sitting in the middle of a football stadium

The Strong Force The strong force holds protons and neutrons together in the nucleus The force becomes weak the father apart the protons and neutrons are from each other The more protons and neutrons in the nucleus, the less strongly they are held together Ex: large atoms like Uranium

Radioactivity When the strong force is not large enough to hold the nucleus together, it will decay and give off matter and energy Again, this is most common in large atoms Ex: 84 protons or more Exception, smaller atoms like C-14 Elements 93 and on were created in a lab

Isotopes All atoms of a certain element have the same number of protons If an atom has a different number of neutrons than usual, it is called an isotope These atoms are less stable and therefore radioactive Ex: C-12 verses C-14

Discovering Radioactivity Henri Becquerel discovered radioactivity in his lab in 1896 using uranium Later, Marie and Pierre Curie discovered polonium and radium What are the atomic numbers of these three elements?

Alpha Particles Alpha radiation emits an alpha particle 2 protons and 2 neutrons It is the same as a helium nucleus Alpha particles are the least penetrating form of radiation Cannot pass through a sheet of paper! Can damage cells inside your body

Transmutation When an atom emits an alpha particle, it has lost two protons and therefore is not the same element It has transmutated into a new element Ex: Polonium (84 protons) transmutates into Lead (82 protons)

Beta Particles A neutron decays into a proton and releases an electron (called a beta particle) So a proton has been added which changes the element Ex: Iodine (53 protons) becomes Xenon (54 protons) CAN pass through paper and damages body cells Stopped by aluminum foil

Gamma Rays Gamma rays are a form of radiation called electromagnetic waves They carry energy and are the most damaging Has no mass and no charge Only lead and concrete can stop them

Name Mass Charge Alpha 4 +2 Beta .0005 -1 Gamma 0 0

Half-Life The time it takes for a half an element to decay is called its half-life The original element is called the parent The new element after decay is called the daughter

Half Life Practice Problem The half-life of Pa-234 is 6.75 hr. How much of a sample of this isotope remains after 20.25 hours?

Common Half-Lives Isotope Name Half-Life Hydrogen-3 12.3 years Lead-212 10.6 hours Carbon-14 5,730 years Polonium-194 0.7 seconds Uranium-235 7.04 x 10^8 years Iodine-131 8.04 days

Dating Scientists use radioactive decay to calculate the age of rocks, fossils, etc. Carbon-14 exists in all organic matter and can be used to date items less than 50,000 years old Uranium-235 is often used to date rocks

Detecting Radioactivity Cloud and bubble chambers are used to detect alpha or beta particle radiation Electroscopes are used to detect electric charges Geiger counters determine the intensity of the radiation present by the number of clicks heard

Background Radiation Low level radiation is emitted by rocks, soil, and the atmosphere It is all around us. Sources of this radiation are radon gas decay from the earth’s crust, cosmic rays that hit the top of earth’s atmosphere, and naturally occurring radiation within your body (C-14)

Nuclear Fission Nuclear fission is the process of splitting a nucleus into two smaller masses This releases a tremendous amount of energy An ongoing series of fission reactions is called a chain reaction

Critical Mass Controlled chain reactions are needed for electricity and nuclear weapons purposes Scientists must experiment to find the critical mass needed to keep the reaction going

Nuclear Fusion Two nuclei are combined to form a new one with a larger mass This is done when the temperature reaches millions of degrees Celsius Ex: The sun undergoes Hydrogen fusion into Helium The sun has enough Hydrogen to continue its fusion for another 5 billion years

Using Nuclear Reactions in Medicine Scientists use tracers to follow molecules through your body to see how an organ is functioning Ex: Patients must drink radioactive iodine to allow doctors to see how their thyroid gland (in the neck area) is functioning Radiation can be used to stop some types of cancer cells from multiplying Gamma rays can be used to treat tumors