Classifying the Elements

• French chemist Antoine Lavoisier grouped the elements as metals and nonmetals


  1789
• German physicist Johann Wolfang Döbereiner observed similarities in physical and chemical properties of certain elements

• Döbereiner's observation

  1. Arranged elements in groups of three in increasing order of atomic weight and called them triads

  2. Observed that some properties of the middle element, such as atomic weight and density, approximated the average value of these properties in the other two in each triad
• First international conference of chemistry in Karlsruhe, Germany


  date 1860
• Karlsruhe, Germany, in 1860 they concluded that hydrogen would be assigned the atomic weight of 1 and the atomic weight of other elements would be decided by comparison with hydrogen
• John Newlands


  British chemist who was the first to arrange the elements into a periodic table with increasing order of atomic masses
• Newlands' law of octaves


  • Every eight elements had similar properties
  • He arranged the elements in eight groups but left no gaps for undiscovered elements
• Russian chemist Dmitri Mendeleev created the framework that became the modern periodic table


  1869
• Mendeleev's process for creating the periodic table

  1. Arranging elements according to atomic weight

  2. Rearranging elements that did not fit into a group
• Eka-aluminium


  An element with properties similar to aluminium, predicted by Mendeleev
• Eka-aluminium was later discovered as gallium
• German chemist Lothar Meyer produced a version of the periodic table similar to Mendeleev's


  1870
• Lothar Meyer left gaps for undiscovered elements but never predicted their properties
• The Royal Society of London awarded the Davy Medal to both Mendeleev and Meyer

  1882
• The later discovery of elements predicted by Mendeleev, including gallium (1875), scandium (1879) and germanium (1886), verified his predictions and his periodic table won universal recognition
• The 101st element was named mendelevium in Mendeleev's honor

  1955
• The concept of sub-atomic particles did not exist in the 19th century
• English physicist Henry Moseley used X-rays to measure the wavelengths of elements and correlated these measurements to their atomic numbers

  1913
• Moseley then rearranged the elements in the periodic table on the basis of atomic numbers, which helped explain disparities in earlier versions that had used atomic masses
• Periodic table

  • Horizontal rows are called periods, with metals in the extreme left and nonmetals on the right
  • Vertical columns, called groups, consist of elements with similar chemical properties
• The periodic table provides information about the atomic structure of the elements and the chemical similarities or dissimilarities between them
• Scientists use the periodic table to study chemicals and design experiments
• The periodic table is used to develop chemicals used in the pharmaceutical and cosmetics industries and batteries used in technological devices