Atomic Structure

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”

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

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

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

Other uses of isotopes… Carbon Dating (carbon-14) Smoke Detectors (americium-241) Agricultural Research (carbon-14, Phosphorous-32)

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

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 = (0.7543 X 35 u) + (0.2447 X 37 u) = 26.40 + 9.05 u = 35.45 u

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

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?

Radioisotope HALF-LIFE 2 half-lives 60 a 12 g 6 g 3g Cesium-137

Homework Worksheet + text questions Old Book Pg. 29 # 7, 8 Pg. 32 # 9 New Book Pg. 29 # 2, 6, 8