The Periodic Table 5.1 Organizing the Elements

What will we learn? How was the original periodic table organized? What evidence was used to verify the usefulness of the table?

The Search for Order There were only 17 elements identified by 1750 Antimony, Bismuth, Carbon, Copper, Gold, Iron, Lead, Mercury, Platinum, Silver, Sulfur, Tin, Zinc, Arsenic, Phosphorus, Cobalt, Nickel

Order of the Table continued By the 1860’s, more than 60 elements were known An early French chemist, Antoine Lavoisier, organized the elements Metals, nonmetals, gases, earths

Order continued… 1829 – Law of Triads – Elements with similar properties came in groups of – Law of Octaves – Every eight elements would have similar properties

Mendeleev’s Period Table Mendeleev was writing a textbook for his chemistry class (His last was referenced until 1947) He was having problems explaining how certain elements react

The Idea Mendeleev made 63 cards, one for each element Each card had the symbol, weight, and important properties (how it reacts with oxygen or water)

The Idea continued… Mendeleev ordered the cards by their mass and properties Some masses were not right, so he shifted the cards by properties Some cards did not work unless he left gaps – elements not yet known

Mendeleev’s Table Within a column, mass increased from top to bottom Periodic – properties repeat from row to row Organized by MASS – did not know about the proton

Mendeleev’s Prediction Many elements were still unknown, so the table was incomplete The gaps were unknown elements His table made predictions about future elements

Evidence Supporting Mendeleev’s Table New elements were discovered – Gallium was “eka-aluminum” – Scandium was “eka-boron” – Germanium was “eka-silicon” Noble gases became a whole new group when discovered

The Fundamental Pattern Leave gaps for things unknown – Some elements were not known – As new elements were discovered, Mendeleev changed his table to incorporate them, filling in the gaps

Fundamental Pattern continued… It is okay to ignore accepted “knowledge” – Some masses were incorrect – Beryllium oxide should have been BeO instead of Be 2 O 3

Fundamental Pattern continued… D o not get locked in one way to do things Some elements in Mendeleev’s table were out of order Tellurium has a higher mass, but he put it before iodine because of its properties