2 Organizing the Elements In the late 1800s, Dmitri Mendeleev searched for a way to organize the elementsHis first arrangement was done by increasing atomic massesFound a patternChemical properties in lighter elements were repeating in heavier elementsThe pattern was PeriodicThe arrangement is now known as the periodic tableMendeleev’s table was so well constructed that he was able to predict the location of elements that had not yet been discovered.
3 Improving the Periodic Table Mendeleev’s table was arranged by atomic massBut there were some spots were atomic mass placement and atomic properties didn’t make senseCobalt and NickelIn 1913, Henry Moseley proposed a table arranged by increasing atomic numberThis change corrected the problems found in Mendeleev’s tableMoseley’s arrangement is the one used in the modern table of elements
4 The Atom and the Periodic Table The vertical columns of the periodic table are known as groupsThe atoms of elements found in the same family have similar propertiesThis is due to the number of electrons in the outer energy level
5 Electron Cloud Structure Electrons in the electron cloud have different energiesThe differences are modeled by placing them in energy levels.Low energy Close to the nucleusHigh energy Further away from the nucleusLabeled from 1 to 7Energy level 1 can hold up to two electronsEnergy level 2 can hold up to 8 electronEnergy level 3 can hold up to 18 electronsA complete and stable outer energy level will have 8 electronsSooo…elements in the same column have the same number of electrons in the outer energy level
6 Rows on the TableAs you go across the table, an electron is added to the outer shell and one proton is added to the nucleusThe row tells you with energy level the outer most electrons are located inThe rows are called periods
7 Electron Dot DiagramsElectron dot diagrams were introduced by G.N LewisThey are a short hand way of showing how many electrons are in the outer energy levelThey are also used to show how atoms combine to form compoundsElectron dot diagrams will be the same for all elements in a column