Development of the periodic table

Development of the ple

John Dalton

arranged elements by atomic weight

Dobereiner

• Law of Triads

  • groups of 3 based on appearance and reaction

• most did not fit

Newlands

• Law of Octaves

  • 7 groups of 8 by similar properties

• assumed all elements were found

• forced elements that didn’t fit pattern

• metals and non-metals in same groups

Mendeleev

• order of atomic weight

• gaps for undiscovered elements + predicted properties

• changed places to fit pattern so elements in the same group had similar chemical and physical properties

Modern periodic table

• arranged by atomic number

• metals on the left and non-metals on the right

• groups and periods

• metals from positive ions

• non-metals form negative ions