Isotopes Atoms of an element (same # p+) that differ in their number of neutrons

Transcription

1 Isotopes Atoms of an element (same # p+) that differ in their number of neutrons Radio-isotopes Isotope of an element that is UNSTABLE. They spontaneously emit particles (energy) in order to achieve a lower, more stable energy state - nuclear reactions. Chemical Reaction number and type of atoms conserved! atoms re-arranged to form new substances ATOMS MAINTAIN THEIR IDENTITY! vs.

2 Nuclear Reaction Unstable ISOTOPES emit NUCLEAR PARTICLES in order to become more stable The IDENTITY of an ATOM changes when it's nucleus changes! Nuclear Reactions involve the formation of ATOMS OF DIFFERENT ELEMENTS Chemical Reaction CHANGE OCCURS OUTSIDE THE NUCLEUS (INVOLVES THE THE ELECTRONS). vs. Nuclear Reaction CHANGE OCCURS INSIDE THE NUCLEUS (INVOLVES THE PROTONS & NEUTRONS)

3 Types of Radiation (Helium Nucleus) (Electron) (Energy) When an atom experiences an alpha decay, it gives off an alpha particle made up of two protons and two neutrons which come directly from its nucleus. The alpha particle is the equivalent to the nucleus of the helium atom and has a mass number of 4, two protons and two neutrons. There are no electrons, so the charge is +2. Giving off an alpha particle causes the mass number of the original element to decrease by 4 and the atomic number to decrease by 2, creating a new element.

4 Atomic Number # Protons! Mass Number # Protons & Neutrons Process Symbol Change in Z Change in A Charge alpha particle emission U He Pb He 238 U 92 = Th = He 2 = Rn + = He 2

5 Beta Decay Another way in which an isotope can decay is by the emission of a beta particle, which is a very high energy electron. The electron does not come from the electron cloud around the nucleus, however. It is produced by the decay of a neutron into a proton and an electron, with the electron then being expelled from the nucleus at a very high rate of speed. Because electrons are very small and only a tiny fraction of an atom's mass, the loss of a single electron will have no effect on the mass number of the atom. The mass number on the periodic table will remain the same. However, because a neutron has been changed into a proton, the atomic number of the new atom or isotope is increased by one What happens when electron emission (beta decay) occurs? What effect does the loss of an electron have on the mass of an atom which has undergone a beta decay?

6 Atomic Number # Protons! Mass Number # Protons & Neutrons Process Symbol Change in Z Change in A Examples beta particle emission +1 0 See Below Atomic Number # Protons! Mass Number # Protons & Neutrons Process Symbol Change in Z Change in A Examples gamma ray emission 0 0 See Below 5726 Fe Fe Sn +

7 Alpha ( Types of Radiation ) - positively charged Beta ( ) - negatively charged Gamma ( ) - pure energy Penetrating Power of Radiation piece of paper wood several feet of lead or concrete

8 Review: Types of Nuclear Decay "Alpha" Types of Nuclear Decay What is REALLY happening...

9 Types of Nuclear Decay December 07, 2010 Writing Nuclear Decays "Alpha" Po 4 2 He +

10 Atomic Number # Protons! Mass Number # Protons & Neutrons Process Symbol Change in Z Change in A Examples positron emission 0 1 e -1 0 See Below Na Ne e 15 7 N e Atomic Number # Protons! Mass Number # Protons & Neutrons Process Symbol Change in Z Change in A Examples neutron emission 1 0 n 0-1 See Below 13 4 Be 12 4 Be n 4 2 He n

11 Atomic Number # Protons! Mass Number # Protons & Neutrons Process Symbol Change in Z Change in A Examples fusion various various See Below 2 1 H H 3 2 He n He 4 2 He e Atomic Number # Protons! Mass Number # Protons & Neutrons Process Symbol Change in Z Change in A Examples fission various various See Below U Ba Kr n Mo Sn n

12 Webquest: Nuclear Chemistry: Radioactivity Nuclear Reactors Assignment: U-238 Decay WS

13 Symbol Type of Decay Half - Life Decay Product Write Reaction for this step U-238 alpha 4.5 billion years Th U --> Th He 238 U 92 From the Periodic Table 234 Th 90 From the Periodic Table Symbol Type of Decay Half - Life Decay Product Write Reaction for this step U-238 alpha Th-234 beta 4.5 billion years 24.1 days Th U --> Th He Th --> e Trying to find this!

14 Key Questions 6. Can a nuclear reaction turn a proton into a neutron or a neutron into a proton? If it cannot, explain why not. If it CAN occur, describe how. December 07, I Xe e ( ) How is mass number changing with this decay? How is atomic number changing with this decay? IF mass number and atomic number, then a must be converted into a. Transmutation When the nucleus of an atom is bombarded by a particle, resulting in the formation of a new element. Bombarding particle could be: - alpha - neutron - proton Example: Bombard 14 N with an 7 alpha particle AND GET 18 F, an ISOTOPE of 9 Fluorine that is not found in nature.

15 Half Life The amount of time it takes for half of the NUCLEI in a sample of a radioisotope to decay. December 07, 2010 Assignment: plural of nucleus SMALL SCALE LAB Radioactivity & Half life Half Life The amount of time it takes for half of the NUCLEI in a sample of a radioisotope to decay. plural of nucleus

16 Half Life You will be asked to solve FOUR different types of half-life problems... December 07, 2010 Type 1: How much radioactive substance remains? Type 3: How much radioactive substance was originally present? Type 2: What is the half-life? Type 4: How much time has passed? Half Life Type 1: Example: How much of a 120 g sample of I-131 will remain after 40 days, if the half life is 8 days? Step 1 Determine # half lifes: 40 days / 8 = 5 Step 2 & 3 Make a table & complete it! # of half lifes Amount (g) Time (days) g

17 Half Life Type 2: Example: A sample H-3 currently has a mass of 2 grams. The original mass of the sample was 16 grams. 36 years have passed. What is the half life? Step 1 Determine # half lifes: Use the table! Step 2 Divide total time by # half lifes! # of half lifes Amount (g) Time (days) 0 16 g

18 Half Life Type 3: Example: A sample Pm-147 currently has a mass of 3 grams. The half life is 2.5 years. How much was present in the sample 10 years ago? Step 1 Determine # half lifes: 10 yrs / 2.5 = 4 Step 2 & 3 Make a table & complete it! # of half lifes Amount (g) Time (yrs) 0? g g 10

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20 Half Life Type 4: Example: A sample Cs-143 currently has a mass of 3 grams. The original mass of the sample was 24 grams. The half life is 2.1 years. How much time has passed? Step 1 Determine # half lifes: how long does it take do decay to 3 grams from 24? Use the table! # of half lifes Amount (g) Time (days) December 07, g

21 Half-Life Problems For every problem you will do the following: 1 - Identify Type 2 - Find example in notes 3 - Set up and Solve You CANNOT ask questions until you have done the first two steps from above!

22 Half-Life Problems December 07, 2010 #1. Change 1.75 g to 1.25 g. #2. #3. #4. Assume that you start with 100%. #5. Assume total amount of time is 24 hours. Complete and balance nuclear decay equations For every problem you will do the following: 1 - Identify Particle (use Nuclear Chemistry: Radiation packet) 2 - Convert given isotope into nuclear symbol 3 - Set-up decay (given isotope 3 - Solve + particle) You CANNOT ask questions until you have done the first three steps from above!

23 Complete and balance nuclear decay equations A. aluminum-26 undergoes a positron emission. December 07, : 0 1 e 2: Al 3: Al e 12 Mg Uses and Applications of Nuclear Chemistry Medicine - Chemotherapy - Tracers Energy Fission - Nuclear Bomb Power Plants Fusion - Sun

24 Medicine Chemotherapy Pro: Drug attacks reproducing cells. Cancer cells rapidly reproduce, and so are targeted and killed. December 07, 2010 Con: Normal cells reproduce as well, and so they are killed as well, which is why patients are often VERY ill during chemotherapy treatments. Drug with radioactive isotope incorporated. Drug accumulates to a toxic level within the cell and the cell dies. Medicine Tracers Used to map the flow of molecules through the body.

25 Energy Nuclear Power Uses energy released from fission reaction which... Heats water to steam Steam turns turbine Turbine generates electricity! December 07, 2010 Animation (2) Steam generated (3) Steam turns turbine & electricity made! (1) Water gets heated to VERY high temperatures by energy released from FISSION reaction in core

26 Reactor Core December 07, 2010 Rods slow down chain reaction Water Where fission is occuring Also slows down chain reaction The Atom Bomb "fission bomb" Critical mass: mass of fissionable material that is required to sustain an uncontrolled chain reaction. -chemical explosion removes "barrier" -neutron "bullet" starts chain reaction of combined masses

27 Fusion December 07, 2010 Occurs when small nuclei combine to form one nucleus of a larger mass Only occurs at VERY HIGH temperatures! Is how we get energy from the sun 1 st Stage 2 nd Stage The Hydrogen Bomb Fision bomb used to create conditions of temperature & pressure required to start fusion bombs in 2nd and 3rd stages. 3 rd Stage

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