Development of the Periodic Table

1. 1803 - John Dalton

   • Combined research with known Laws to propose the first modern Atomic Theory

2. 1829 - Döbereiner

   • Triads: Organized known elements into groups of 3 according to their properties

   • Noticed the middle element had properties approximately between the other 2

3. 1865 - Newlands

   • Octaves: Organized elements into groups of 8

   • Understood that properties repeated

4. 1869-1871 - Mendeleev

   • Wrote properties of each element on cards and arranged them according to properties

   • First Modern Periodic Table

   • Arranged elements even when:

     • Masses weren't in order (e.g. Te, I)

     • There wasn't a known element that fit

5. 1897 - J.J. Thomson

   • Cathode Ray Tube experiments (electrons discovered)

6. 1911 - Rutherford

   • Gold Foil Experiment (nucleus discovered)

7. 1913 - Henry Moseley

   • Determined atomic number for each element using x-ray spectroscopy

   • Found frequencies of x-rays are proportional to square of a number nearly equal to atomic number

Modern Periodic Table

Structure

• Organized by periods (rows) and groups (columns)

• "Stair-Step" Line divides metals and nonmetals

Element Classifications

1. Metals

   • Most are solids

   • Good conductors of heat and electricity

   • Lustrous (shiny, reflect light)

   • Malleable (can be pounded into thin sheets)

   • Ductile (can be pulled into thin wires)

   • Form alloys to improve properties

2. Metalloids

   • All are solids

   • Less conductive than metals

   • Can be shiny or dull

   • Some are malleable and ductile

   • Tend to be brittle

   • Used in alloys

3. Nonmetals

   • Can be solids, liquids, or gases

   • Poor conductors of heat and electricity (except graphite)

   • Dull appearance

   • Brittle (shatter when hit)

Groups and Families

• Families: Groups of elements with similar properties

• Main Group Elements:

  • s and p blocks

  • Properties follow predictable patterns across periods and within groups

  • Valence electrons determine chemical behavior