Logged out
Access All our Essays in an Instant
Swap your work for FREE access, or pay £4.99 for instant access
A History of the Periodic Table.
Member rating: No Rating | Words: | Submitted: Tue Mar 02 2004
Page Preview
On the left is an image preview of every page of this document, and below are the first 150 words with formatting removed:
A HISTORY OF THE PERIODIC TABLE Introduction Döbereiners Triads In the early 1800s Dobereiner noted that many of the known elements could be arranged in triads - a group of 3 chemically similar elements. Two of these triads are Chlorine, Bromine, Iodine and Lithium, Sodium Potassium. Döbereiner's Triads Ca 40.1 Sr 87.6 Ba 137.3 S 32.1 Se 79.0 Te 127.6 Cl 35.5 Br 79.9 I 126.9 He showed that when the three elements in each triad were arranged in order of Relative Atomic Mass, the middle element had properties intermediate to those of the other two elements. Also the Relative Atomic Mass of the middle element was close to the mean Relative atomic Masses of the other two elements. E.g. In the triad Chlorine, Bromine and Iodine the Relative Atomic Mass of Bromine (79.9) was close to the mean Relative Atomic Mass of Chlorine and Iodine (35.5 + 126.9)/2=81.2. However most chemists considered this to be a coincidence, as too few elements were known, values of atomic masses were uncertain and the triads covered...
To see the full version of this document, and 145,348 others
