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Name Date 5.1 Structure of the Periodic Table 1. Fill in the missing data on the table below. Element Protons Neutrons Ca Electrons Mass number 20 Atomic number 20 4 146 2 92 9 14 19 28 2. Using the periodic table in your textbook, find the name, atomic number, and average atomic mass of the following elements. Element Name Atomic number Average atomic mass K Ag Sn Y Answer the following question in complete sentences. 3. Why did Dmitri Mendeleev develop the periodic table? 4. What is the difference between the periodic table developed by Mendeleev and the one we use today? Protons, Neutrons, and Electrons The atomic number of an atom is the number of protons in each atom of that element. Atomic Number = Proton Number Because atoms are electrically neutral, the atomic number is also the number of electrons. Atomic Number = Electron Number The mass number tells you the number of protons and neutrons in an atom. By subtracting the atomic number from the mass number, you can determine the number of neutrons. Mass Number – Atomic Number = Neutrons Use this information to complete the table. Element Atomic number Mass number Helium 2 4 Nitrogen 7 14 Carbon 6 12 Sodium 11 12 Iron 26 30 Copper 64 Silver 47 Lithium 3 Boron 11 Neon 20 Aluminum 27 Hydrogen 1 Electrons 29 7 9 12 Neutrons 61 Beryllium Magnesium Protons 4 5 10 13 24 0 Families of Elements Use the periodic table in your book to fill in the missing data below. Description Family # Number of electrons in outer energy level Halogens Silicon Alkaline earth Metals Hydrogen Aluminum Nobel gases Oxygen Alkali metals Using the periodic table, give the name of each of these elements and indicate whether it belongs to the alkali metal or alkaline earth metal family. Element Be Cs Li Ca Element Name Family Name