Nuclear Reactions Ch. 21

Discovery of Radiation Henri Becquerel – discovered elements give off radiation – Photograph film became exposed after being in a drawer with a piece of uranium Marie Curie – named emissions from unstable nucleus “radioactivity”

Nuclear Reactions Changing the number of protons changes the elements identity Changing the number of protons changes the elements identity -must clearly mark the element with the isotope information -not all isotopes are radioactive

Radioactive Decay Alpha Decay Releases Alpha particles Releases Alpha particles Helium nuclei (2 p + and 2 n 0 ) Helium nuclei (2 p + and 2 n 0 ) – large particle with low energy level so it does not pass through many layers – stopped by paper or clothing New element loses 2 p + and mass # goes down by 4 New element loses 2 p + and mass # goes down by 4 Uranium-238 starts with alpha decay

Radioactive Decay Beta Decay Releases Beta particles; high-energy “electron” Releases Beta particles; high-energy “electron” A neutron broken down into a p + and an e - A neutron broken down into a p + and an e - Small, light, and high energy, so they pass through more layers than alpha Small, light, and high energy, so they pass through more layers than alpha Stopped by metal, think wood, thick clothing Stopped by metal, think wood, thick clothing New element gains 1 to atomic number since there is 1 more proton, mass number is the same New element gains 1 to atomic number since there is 1 more proton, mass number is the same

Radioactive Decay Gamma Decay Releases Gamma rays; super high energy with no mass or charge Releases Gamma rays; super high energy with no mass or charge Penetrate many layers Penetrate many layers Stopped by think layers of lead or very thick layers of concrete Stopped by think layers of lead or very thick layers of concrete – Dangerous to DNA and cells, will cause mutations and cell death Only energy is released so gamma decay does not change element, however gamma rays do not occur alone, they are produced by other forms of decay Only energy is released so gamma decay does not change element, however gamma rays do not occur alone, they are produced by other forms of decay

Questions This reaction is an example of __________. 210 Po → 206 Pb + __________ A) alpha decay B) positron emission C) gamma emission D) beta emission The missing product from this reaction is 121 I → 121 Te + __________ A) 0 e B) 0 γ C) 4 He D) 1 n E) 0 e

Half-Life The time is takes for half the amount of an isotope to decay; t 1/2 The time is takes for half the amount of an isotope to decay; t 1/2 Can range from fractions of a second to billions of years Can range from fractions of a second to billions of years Its used to find the age of objects Its used to find the age of objects – C-14, U-238, Rb-87, K-40

Calculating Half-Life N t = N 0 x 0.5 (y) N t = N 0 x 0.5 (y) N t is the amount of isotope left N t is the amount of isotope left N 0 is the original amount of the isotope N 0 is the original amount of the isotope y is the number of “half-lives”; time/half-life y is the number of “half-lives”; time/half-life Ex. B-131 has a half-life of 12 days. How much of a sample 50g will be left after 72 days? N t = 50g x 0.5 (72/12) N t = 50g x 0.5 (6) N t = 0.78g

Question 131 I has a half-life of 8.04 days. Assuming you start with a 1.53 mg sample of 131 I, how many mg will remain after 13.0 days __________ ? A)0.440 B) C) D) E) N t = N 0 x 0.5 (y) N t = 1.53mg x 0.5 (13.0/8.04) N t = 0.499

C-14 Dating C-14 is used to find the age of fossils C-14 is used to find the age of fossils C-14 is constant while we are alive, but after death is starts to run out C-14 is constant while we are alive, but after death is starts to run out Half-life is 5730 years, so if half the amount is present then the object is about 5730 years old Half-life is 5730 years, so if half the amount is present then the object is about 5730 years old

Nuclear Reactions and Energy Huge amounts of power released as the nuclear reactions convert mass into energy Huge amounts of power released as the nuclear reactions convert mass into energy E=mc 2 E=mc 2 Small amount of mass can change into a huge amount of energy Small amount of mass can change into a huge amount of energy

Nuclear Fission Atomic nucleus splits into two or more large fragments Atomic nucleus splits into two or more large fragments – causes a chain reaction – if reaction is too fast it explodes Fission Reactors Fission Reactors – U-235 reaction produces heat which steams water, the steam turns a turbine which generates electricity – do not produce harmful gases like other power plants – produces nuclear waste which is difficult to dispose of plus there could be radiation leaks

Nuclear Fusion Two or more nuclei combine to form a larger nucleus Two or more nuclei combine to form a larger nucleus – energy process inside stars; hydrogen makes helium – when the star goes supernova, all other heavier elements are created Deuterium Tritium Fusion Reactors Fusion Reactors -no waste products and no radiation is produced -however the reaction requires a lot of starting energy

Using Radiation Radio isotopes Radio isotopes – Can be injected into the body and tracked to see if there are troubled areas, holes, cuts, etc. – Can be added to a water supply to trace where chemicals will end up in an ecosystem – Can be used with subatomic particles to create new artificial elements

Mid-term Lewis Dot Diagrams Periodic Trends – Atomic Radius, Ion Size, Electronegative, etc… Properties of Metal, Non-metals, and Metalloids Types of Mixtures/ Pure substances/ Elements vs. Compounds Chemical properties/change vs. Physical properties/change Valance Electrons/ Ion Charge Nuclear Decay Ionic vs. Covalent Bonding Group Trends on the Periodic Table Calculating Mass Percent Calculating Atomic mass Significant figures Calculating wavelength Calculating Half-Life Solutions/ Solutes/ Solvents Balancing Equations

Maintaining the Law of Conservation of Mass Maintaining the Law of Conservation of Mass NaOH +CO 2 -> Na 2 CO 3 + H 2 O 2NaOH +CO 2 -> Na 2 CO 3 + H 2 O NaOHC Reactants1311 Products2421 NaOHC Reactants2421 Products2421

Practice MgCl 2 + AgNO 3 -> Mg(NO 3 ) 2 + AgCl MgCl 2 + 2AgNO 3 -> Mg(NO 3 ) 2 + 2AgCl CO 2 + LiOH -> Li 2 CO 3 + H 2 O CO 2 + 2LiOH -> Li 2 CO 3 + H 2 O Cl 2 + NaBr -> NaCl +Br 2 Cl 2 + 2NaBr -> 2NaCl +Br 2