Nuclear Chemistry powerpoint - PC\|MAC

Nuclear Chemistry powerpoint - PC\|MAC

NUCLEAR CHEMISTRY Chapter 21 Introduction to Nuclear Chemistry Nuclear chemistry is the study of the structure of and the they undergo. atomic nuclei changes Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or

rays Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, although they may be rearranged Atoms often converted into atoms of another element Chemical vs. Nuclear Reactions Chemical Reactions

Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, Atoms often converted into although they may be rearranged atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Chemical vs. Nuclear Reactions Chemical Reactions Nuclear Reactions

Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, Atoms often converted into although they may be rearranged atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes Chemical vs. Nuclear Reactions Chemical Reactions

Nuclear Reactions Occur when bonds are broken Occur when nuclei emit particles and/or rays Atoms remain unchanged, Atoms often converted into although they may be rearranged atoms of another element Involve only valence electrons May involve protons, neutrons, and electrons Associated with small energy changes Associated with large energy changes Reaction rate influenced by temperature, particle size,

concentration, etc. Reaction rate is not influenced by temperature, particle size, concentration, etc. The Discovery of Radioactivity (1895 1898): Roentgenfound that invisible rays were emitted when electrons bombarded the surface of certain materials. Becquerel accidently discovered that phosphorescent salts produced spontaneous emissions that darkened photographic plates uranium

The Discovery of Radioactivity (1895 1898): Marie Curie isolated the components of uranium atoms emitting the rays process by Radioactivity which atoms emit rays or particles the penetrating rays Radiation and particles by a emitted radioactive source.

Radiation can be damaging to living organisms The Discovery of Radioactivity (1895 1898): polonium radium contradicted identified 2 new elements, and on the basis of their radioactivity These findings Daltons theory of indivisible atoms.

The Discovery of Radioactivity (1895 1898): atoms of the same Isotopes element with different numbers of neutrons Radioisotopes isotopes of unstable many few atoms with nuclei (too / neutrons) Radioactive decay when radiation lose unstable nuclei energy by emitting stable

to attain more spontaneous atomic configurations ( process) Alpha radiation Composition Alpha particles, same as helium 4 nuclei 2

Symbol Helium nuclei, He, Charge +2 Mass 4 amu Approximate energy 5 MeV Penetrating power low (0.05 mm body tissue) Shielding these can be blocked by paper or clothing Beta radiation Composition Beta particles, same as an electron Symbol e-, Charge -1 Mass (amu) 1/1837 (practically 0) Approximate energy 0.05 1 MeV

Penetrating power moderate (4 mm body tissue) Shielding These can be blocked by metal foil Gamma radiation Composition High-energy electromagnetic radiation traveling at the speed of light Symbol Charge 0 Mass (amu) 0 Approximate energy 1 MeV Penetrating power high (penetrates body easily) Shielding These can only be blocked by lead or concrete

Review of Atomic Structure Nucleus Electrons 99.9% of the 0.01% of the mass but mass 1/10,000 the size of the atom Review of Atomic Structure Nucleus Electrons 99.9% of the mass but 1/10,000 the size of the atom 0.01% of the mass Composed of Composed of

protons (p+) and electrons (e-) neutrons (n0) Review of Atomic Structure Nucleus Electrons 99.9% of the mass but 1/10,000 the size of the atom 0.01% of the mass Composed of protons (p+) and neutrons (n0) Composed of electrons (e-) Positively charged Negatively charged Review of Atomic Structure

Nucleus Electrons 99.9% of the mass but 1/10,000 the size of the atom 0.01% of the mass Composed of protons (p+) and neutrons (n0) Composed of electrons (e-) Positively charged Negatively charged Strong nuclear force (holds the nucleus together) Weak electrostatic

force (because they are charged negatively Chemical Symbols A chemical symbol looks like mass # 14 6 atomic # C neutrons atomic # mass # To find the number of subtract the from the

, Nuclear Stability not Isotope is completely stable if the nucleus will spontaneously . Elements with atomic #s to are + 0 . ratio of protons:neutrons ( )makes an isotope very stable Example: Carbon 12 has protons and neutrons

decompose 1 20 very stable p :n 1:1 6 6 Nuclear Stability are 21 82 to marginally stable . 1:1.5ratio of protons:neutrons (p : n ) 80 120 Example: Mercury 200 has

Elements with atomic #s + protons and neutrons 0 Nuclear Stability > 82 unstable radioactive UraniumPlutonium Elements with atomic #s are and . Examples:

and Isotopes with greater than 1.5 neutrons per 1 proton are unstable or radioactive Alpha Decay He +2 Alpha decay emission of an alpha 4 by the symbol particle ( ), denoted 2 , because an has 2 protons and 2 neutrons, just like the He nucleus. Charge is because of the 2

. Mass of alpha particle is amu. Alpha decay causes the number to decrease by and the number to decrease by . 4 2 protons 4 mass atomic Alpha Decay Example 1: Write the nuclear equation for the radioactive decay of polonium 210 by alpha emission.

Step 4: 1: Determine 2: 3: Draw the arrow. Write element alpha the other particle. that product you are starting with. (ensuring everything is balanced). Mass # 210 84 Po

Atomic # 206 82 Pb 4 2 He Alpha Decay Example 2: Write the nuclear equation for the radioactive decay of radium 226 by alpha emission. Step 4: 1: Determine 2: 3: Draw the arrow. Write

element alpha the other particle. that product you are starting with. (ensuring everything is balanced). Mass # 226 88 Ra Atomic # 222 86 Rn

4 2 He Beta decay Beta decay emission of a beta particle ( ), a fast moving , denoted 0 by the symbol or . has -1 insignificant mass ( ) and the charge is

because its an . This occurs as a neutron changes into a proton by emitting the negatively charged beta particle Beta decay causes change in number and causes the number to increase by . electron e 0 electron -1 no atomic mass e 1 Beta Decay

Example 1: Write the nuclear equation for the radioactive decay of carbon 14 by beta emission. Step 4: 1: Determine 2: 3: Draw the arrow. Write element beta the particle. other that product you are starting with. (ensuring everything is balanced). Mass #

14 6 C Atomic # 14 7 N e 0 -1 Beta Decay Example 2: Write the nuclear equation for the radioactive decay of zirconium 97 by beta decay.

Step 4: 1: Determine 2: 3: Draw the arrow. Write element beta the particle. other that product you are starting with. (ensuring everything is balanced). Mass # 97 40 Zr

Atomic # 97 41 Nb e 0 -1 Gamma decay electromagnet 0 mass atomic always Gamma rays high-energy radiation, denoted by the symbol

. has no mass ( ) and no charge ( ). Thus, it causes change in or numbers. Gamma rays almost accompany alpha and beta radiation. However, since there is effect on mass number or atomic number, they are usually from nuclear equations. no 0 no omitted Transmutation

Transmutation the of one atom of conversion one element to an atom of a different element radioactive ( decay is one way that this occurs!) Review Type of Particl Change Change Radioact e in Mass in ive Emitte # Atomic Decay d 42

# Alpha 0 -4 -2 -1 He Beta e 0 +1 Gamma 0 0 Half-Life istime the required half Half-life for of a radioisotopes nuclei to

decay into its products. For # any radioisotope, of lives % Remaining 0 1 2 3 4 5 6 100% 50% 25% 12.5% 6.25%

3.125% 1.5625% Half-Life Half-Life 100 90 % Remaining 80 70 60 50 40 30 20 10 0 0 1 2

3 4 # of Half-Lives 5 6 7 Half-Life For example, suppose you have 10.0 grams of strontium 90, which has a half life of 29 years. How much will be of Time remaining after x #number of

years?Amount lives (Years) Remaining (g) You can use a table: 0 1 2 3 4 0 29 58 87 116 10 5 2.5 1.25 0.625

Half-Life Or an equation! initial mass mt = m0 x (0.5) n mass remaining # of half-live Half-Life Example 1: If gallium 68 has a half-life of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________ Half-Life

Example 2: Cobalt 60, with a half-life of 5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years? ______________ Half-Life Example 3: Iron-59 is used in medicine to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? ______________ Half-Life Example 4: The half-life of polonium-218 is 3.0 minutes. If you start with 20.0 g, how long will it take before only 1.25 g remains? ______________ Half-Life

Example 5: A sample initially contains 150.0 mg of radon-222. After 11.4 days, the sample contains 18.75 mg of radon222. Calculate the half-life. Nuclear Reactions Characteristics: Isotopes of one element are into isotopes of another element Contents of the change amounts of are released changed nucleus energy Large

Types of Nuclear Reactions Radioactive decay alpha and beta particles and gamma ray emission Nuclear disintegration emissionneutron of a or proton Nuclear Fission of a nucleus Fission splitting - Very heavy nucleus is split into two approximately fragments

equal reaction releases several neutrons Chain which more nuclei split - If controlled, energy is released slowly (like in ) Reaction nuclear reactors control depends on reducing the of speed the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction absorbing de rate).

Nuclear Fission - 1st controlled nuclear reaction in December 1942. 1st uncontrolled nuclear explosion occurred July 1945. - Examples atomic bomb, current nuclear power plants Nuclear Fusion of a nuclei combining Fusion - Two nuclei combine to form a light single heavier nucleus - Does not occur under standard conditions

+ + ( repels ) inexpensiv - Advantages compared to fission no radioactive waste , large - Disadvantages - requires control amount start of energy to , difficult to

- Examples energy output of stars, hydrogen bomb, future nuclear power plants Uses of Radiation Radioactive dating - Carbon - 14 used to determine the age of an object that was once alive. Radioactive tracing of diseases Iodine 131 used to detect thyroid problems. Treatment of some cancers (cobalt 60 and cesium 137) cancer cells are more sensitive to radiation than normal, healthy cells Uses of Radiation

tungsten - 182 generally is used to generate X-rays thorium 232 used in gas lanterns and welding plutonium 238 used in space probes and satellites americium 241 in smoke detectors.

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