Unit 4 - The Periodic Table Currently there are over 110 elements. They must be organized in order to study them easily Originally organized by chemical and physical properties. Chemical Property Describes how a substance behaves in a chemical reaction Usually ends up with a different substance How substance interacts with others

I. History of the Periodic Table A. Johann Dobereiner 1829 Noticed that some elements have similar properties Created sets of elements called “Triads” Lightest element was on top, heaviest on bottom Br Cl Li Na I K Br Na I K While most people assumed this was coincidence, Dobereiner’s work laid the groundwork for future scientists

Organized elements by increasing mass B. John Newlands 1864 Organized elements by increasing mass Noticed that every 8th element had similar properties Li Be B C N O F Na Mg “Law of Octaves” As new elements were discovered, this theory broke down. But Newlands determined that elements properties were related to their mass C. Dimitri Mendeleev 1869 Created the first Periodic Table of Elements Organized elements by increasing mass Aka Santa Claus! Similar elements were put in the same column Left blank spaces in his table for undiscovered elements Li Be B C N O F Na Mg Si ? Accurately predicted the chemical and physical properties of these unknown elements

Hmm… I think I can improve this! D. Henry Moseley 1914 Used x-ray crystallography to improve on Mendeleev’s table Organized elements by increasing ATOMIC NUMBER Hmm… I think I can improve this! Basically, the same table as Mendeleev Created the Modern Periodic Law “Properties of Elements are periodic functions of their atomic numbers” When the elements are lined up by atomic number, their properties begin to repeat.

II. Organization of the Periodic Table A. Periods Period is a horizontal row 1st period = H, He 2nd period = Li, Be, … Ne The Period number tells you how many principal energy levels are used Ex. K is in the 4th period, so it has 4 principal energy levels Lanthanide and Actinide series F sublevel is being filled Actually belong in the normal table, but it is cut out to make it shorter

C. Groups Vertical Columns aka “Family” Now numbered 1-18 All members of a family have similar chemical reactivity.