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Atomic Structure
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Atomic and Mass Number The number of protons in an atom = atomic number (symbol “Z”) The mass = protons + neutrons (symbol “A”) Mass is measured in atomic mass units (µ) Number of neutrons = mass number – atomic number Standard Atomic Notation: “Biggie over small”
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F Practice 9 19 For each example find the number of protons
number of neutrons number of electrons atomic number mass number A) F 19 9 B) C) An element that has 91 protons and 140 neutrons
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Isotopes and Radioisotopes
Isotopes are different forms of an element having the SAME atomic number but DIFFER in the amount of neutrons (and mass). Radioisotopes: Atoms with an unstable nucleus and decay (or break apart) to produce radioactive particles Three types: alpha (α), beta (β), and gamma (γ) Cl 35 17 37 Cl
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Medical Uses of Isotopes
Used to detect thyroid diseases Iodine–131 Body uses it the same as naturally-occurring iodine (Iodine-127) The thyroid controls how quickly the body burns energy, makes proteins, and controls how sensitive the body should be to other hormones. Iodine in nature is 100% iodine-127 (stable) Iodine-131 is formed in nuclear reactions, it is unstable and undergoes radioactive decay Because these isotopes are absorbed by the thyroid virtually the same way a doctor can use in diagnostic test Sodium iodide, made with iodine-131, is administered and instruments are used to detect radioactive emissions detecting the levels and locations in patients body
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Other uses of isotopes…
Carbon Dating (carbon-14) Smoke Detectors (americium-241) Agricultural Research (carbon-14, Phosphorous-32)
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Isotopic Abundance and Atomic Mass
Different elements have different numbers of isotopes that exist in different relative abundances Ex: An average sample of magnesium contains: 78.7% Mg-24,10.1% Mg-25 and 11.2 % Mg-26 Atomic mass is the weighted average of the masses of all isotopes of that element A weighted average considered not only the values but also the relative abundance of each value
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Calculating Relative Atomic Mass
Calculate the relative atomic mass of chlorine if the relative abundance of Cl-35 is 75.43% and Cl-37 is 24.47%. mCl = (percent abundance of Cl-35 x atomic mass Cl-35) + (percent abundance of Cl-37 X atomic mass Cl-37) mCl = ( X 35 u) + ( X 37 u) = u = u
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Different types of radiation have different penetrating power
Three main types: Alpha (), Beta (), Gamma () Alpha radiation = 2p+, 2n0 same as He nucleus Beta radiation = high energy electrons or positrons Gamma radiation = high energy electromagnetic waves (have no mass and travel at the speed of light) Different types of radiation have different penetrating power
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Radioisotope HALF-LIFE
HALF-LIFE refers to the time for ½ of the original number of radioactive atoms to decay Example: The half-life of cesium-137 is 30a. What mass of cesium-137 would remain from a 12 gram sample after 30a? After 60a?
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Radioisotope HALF-LIFE
2 half-lives 60 a 12 g 6 g 3g Cesium-137
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Homework Worksheet + text questions Old Book Pg. 29 # 7, 8 Pg. 32 # 9
New Book Pg. 29 # 2, 6, 8
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