ORGANIZING ELEMENTS

1. ORGANIZING ELEMENTS

2. Ways to Organize elements • 1. By State • Most elements are SOLID • 11 are gases • 2 are liquids • 2. By Colour and Appearance • Majority of elements are SILVERY, SHINY solids

3. 3. Organization into Metals and Non-metals • Metals • Shiny • Good conductors of electricty • Malleable • Ductile • Non-metals • Not shiny • Poor conductors • Brittle • Semi-metals (metalloids) • Elements that possess some properties associated with metals • 4. Organize by Reactivity • Noble Gases - inert • 5. Organization by Atomic Mass • Organize by relative atomic mass

4. Periodic Table of the Elements • Johann Dobereiner 1829 “Law of Triads” • Regularity in atomic mass of chemically and physically similar elements • Example: Li, Na, K • All soft, very reactive metals • Difference in atomic masses -> 16.1 • BUT: regularity did not generally apply

5. John Newlands 1864 - “Law of Octaves” • Arranged known elements in order of increasing relative atomic mass • Every 8th element had similar chemical and physical properties • BUT: only worked for first 20 elements

6. Dmitri Mendeleev - 1869 “properties of the elements are periodic functions of their relative atomic masses” • Able to organize elements into subgroups • *Left blank spaces • Able to predict elements that had yet to be discovered • BUT: some inconsistencies • Example: Te (127.6), I (126.9) • Physical and chemical properties suggest that the order be reversed

7. Henry Moseley - 1912 • elements are arranged in order of increasing atomic number • Periodic repetition of elements with similar properties • Currently accepted periodic table