Dmitri Mendeleev Arranged elements by increasing atomic mass Predicted properties of missing elements Episode 401

Henry Moseley Discovered that each element has a unique atomic number Arranged elements by increasing atomic number Now all the elements fit into place based on properties Episode 401

Modern Periodic Law Properties of elements repeat when elements are arranged by increasing atomic number Periodic function or repeats Episode 401

Questions about the extended periodic table: Why do you think these elements get pulled out? It makes the periodic table more compact. Which element is in a different column than we are used to? He What happens to the number of energy levels as you begin each new row? Increases by 1 What is the similar characteristic in each column? Electron distribution Episode 401

Elements in the same column: Have similar electron distributions Have same number of valence electrons Electrons lost, gained, or shared Found in the s and p orbital of highest energy level Have similar chemical properties Ne: 1s2 2s2 2p6 Kr: 1s2 2s2 2p6 3s2 4s2 3d10 4p6 Episode 401

Noble Gases Have full outer energy level Have 8 valence electrons Are stable (inert or unreactive) Episode 401

Using the periodic table to find electron distributions: Episode 401

Noble Gas Configuration Shorter way to do electron configurations using noble gases Find noble gas on the end of row before the element and put its symbol in brackets. Use diagonal rule to write the electron distribution for Sn (atomic # 50) 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p2 Use the noble gas distribution to write electron distribution for Sn [Kr] 5s2 4d10 5p2 Episode 401

Noble Gas Configuration Find noble gas on the end of row before the element and put its symbol in brackets. Use diagonal rule to write the electron distribution for Fe (atomic # 26) 1s2 2s2 2p6 3s2 3p6 4s2 3d6 Use the noble gas distribution to write electron distribution for Fe [Ar] 4s2 3d6 Episode 401