Organizing Elements

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Organizing Elements 5.1
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INTRODUCTION

• A. Until 1750, scientists had identified only 17
  elements
• Mainly metals, such as copper and iron
• B. In 1789, Antoine Lovoisier grouped elements
  into 4 categories metals, nonmetals, gases, and
  earths

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MENDELEEV

• A. He organized elements according to their
  atomic mass
• B. He recognized patterns of repeated properties
• C. Created a periodic table arrangement of
  elements in columns based on similar properties
  that repeat

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MENDELEEV, CONT.

• D. 1872 published his table of elements with
  horizontal rows of increasing atomic masses.
  Elements with similar properties were in vertical
  columns.
• - atomic masses increased from left to right and
  from top to bottom
• - elements were in columns according to their
  reactivity to oxygen and hydrogen

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MENDELEEV, CONT.

• E. By using his periodic table, Mendeleev was
  able to predict the properties of several
  undiscovered elements.
• F. He predicted the properties of both gallium
  (Ga) and germanium (Ge) before they were both
  discovered. They were discovered in his
  lifetime, so he was able to prove his theories
  correct.

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Prediction of Gallium (Ga)
PROPERTY PREDICTED ACTUAL
Atomic mass 70 u 69.72 u
Color Dark gray Gray-white
Density 5.9 g/mL 5.9 g/mL
Melting point 25C 29.7C
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MENDELEEV, CONT.

• F. Mendeleevs ability to predict properties of
  undiscovered elements led scientists to accept
  his periodic table.