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Isotope Note Handout Atom Review All matter is made up of elements (e.g. carbon, hydrogen, etc.). The smallest part of an element is called an atom. Atom of different elements contain different numbers of protons. The mass of an atom is almost entirely due to the number of protons and neutrons. The Atom The atom consists of two parts: 1. The nucleus which contains: 2. Orbiting electrons. (Draw the atom in the box and label) Isotopic Notation Mass number = __________________________________________________ Atomic number = ________________________________________________ (Draw the isotopic notation in the box of element X) A= ________________________________ Z= ________________________________ A-Z= _______________________________ ISOTOPES THE NUMBER OF _________________ FOR A GIVEN TYPE OF ATOM _____________________________________________ THE NUMBER OF ____________________________ CAN CHANGE. TWO ATOMS WITH THE SAME NUMBER OF PROTONS BUT DIFFERENT NUMBERS OF NEUTRONS ARE CALLED _________________________. 840945282 Updated On: 4/28/2017 Page 1 of 3 ISOTOPES ISOTOPES ARE ATOMS WITH THE SAME NUMBER OF PROTONS BUT ____________________________ NUMBER OF _____________________________. Examples of Uranium Isotopes 235 238 U A Z Number of protons Number of neutrons U A Z Number of protons Number of neutrons Atomic Weight To calculate the atomic weight (average atomic mass) for a particular element we must consider how much of one isotope of an element exists versus another isotope of the same element. These are the "natural" abundances (% abundance) on earth. Rule for Calculating Atomic Weight To calculate the average atomic weight, each exact atomic weight is multiplied by its percent abundance (expressed as a decimal). Then, add the results together and round off to an appropriate number of significant figures. Example #1: Nitrogen mass number exact weight percent abundance 14 14.003074 99.63 15 15.000108 0.37 This is the solution for nitrogen: (14.003074) (0.9963) + (15.000108) (0.0037) = 14.007 840945282 Updated On: 4/28/2017 Page 2 of 3 Practice Problem # 1 Calculate the average atomic weight for magnesium: mass number exact weight percent abundance 24 23.985042 78.99 25 24.985837 10.00 26 25.982593 11.01 840945282 Updated On: 4/28/2017 Page 3 of 3