The Development of the Periodic Table EQ: What is the historical background for the development of the periodic table?

History 1700’s about 30 known elements - mostly metals and gases Using the line spectra more elements could be identified. Need to organize known elements.

Dobereiner 1800s Classified by triads because of similar chemical properties Also found that atomic mass of smallest and largest element could be averaged to get that of the middle element.

Newlands 1865 Arranges by increasing atomic mass Finds that same properties repeat every 8 elements Law of octaves

Mendeleev 1869 Mendeleev wanted to organize elements to help his students learn. Arranges by mass

Mendeleev Broke the pattern if necessary to keep elements with similar properties together. Predicted existence of missing elements

Moseley 1913 -when bombarded with electrons metals produced X-rays with different frequencies. -these differences were the result of the difference in positive charge in the nucleus of each element.

The atomic number is born!

Mendeleev’s Periodic Table History of the Periodic Table A commemorative stamp collector’s miniature sheet showing some of Mendeleev’s original notes. Horizontal lines like Cr, Mo and W (in the third row down) correspond to today's groups. Note the date, 17 February 1869.

Periodic Law When elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic pattern.

The Periodic Table Chemistry: Periodic Table and More WebElements Periodic Table of the Elements Dynamic Periodic Table The Periodic Table of the Elements, Standard Form

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