Organizing the Elements
Intro to the Periodic Table
Searching for Order…
• In 1750 only 17 elements had been identified
• In 1789 Antoine Lavoisier grouped them into
four categories
– metals, nonmetals, gases, Earths
• Classification systems failed to meet the need
of the growing number of elements
Mendeleev’s Table
• In 1860’s, Mendeleev arranged the 63 known
elements in rows according to increasing
atomic mass
• Elements with similar properties ended up in
the same column
Mendeleev’s Table
Mendeleev’s Table
• In 1860, Mendeleev arranged the 63 known
elements in rows according to increasing
atomic mass
• Elements with similar properties ended up in
the same column
• Periodic Law: Physical and Chemical
properties of elements vary periodically with
increasing atomic mass
Support for Mendeleev’s Table
• Mendeleev left some open spaces on his table
• He theorized that these spaces represented
elements that were yet to be discovered
• As more elements were discovered they fit
Mendeleev’s predictions
– gallium, germanium, scandium
• To test the effectiveness of a model, test the
accuracy of predictions made using the model
Mendeleev’s Table
Mendeleev’s Predictions
Modern Periodic Table
• Henry Moseley
– Develops technique to determine charge on each
nucleus (different number of protons)
– Periodic Table rearranged by increasing atomic
number, not increasing atomic mass
– Some abnormalities from Mendeleev’s original
table are resolved
• Te & I
• Glenn Seaborg
– Movement of Inner Transition Metals
(transuranium elements) to bottom of table