2.1 the development of the periodic table
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Who arranged elements in the order of their atomic weight
John Dalton
When did John Dalton publish a table of elements and in what
In 1808 in his book called A New System Of Chemical Philosophy
Who build on Dalton’s ideas and when
John Newlands in 1864
What did John Newlands do
He arranged the known elements in order of mass but noticed the properties of every eighth element seemed similar, he produced a table showing his ‘law of octaves’
What mistake did John Newlands make
He assumed that all elements had been found. His table only worked for the elements up to calcium but then the pattern broke down. Other scientists refused to accept his ideas
Which scientist cracked the problem and when
Dmitri Mendeleev in 1869
What did Dmitri Mendeleev do?
• he arranged the elements in order of weight and arranged them so that a periodic (regularly occurring pattern) could be seen. • He left gaps for elements that had not yet been discovered • He predicted what properties the undiscovered atoms would have
What did Mendeleev do when elements didn’t fit the pattern?
He changed the order when necessary tp keep elements with similar properties in the same group
What happened in the 20th century that helped the periodic table make sense
Scientists ~ZED began to find out more about the structure of the atom. Only then could they solve this issue of certain elements breaking the periodic pattern. The elements in the periodic table are in order of their number of protons (their atomic number). The existence of isotopes accounted for the oddly heavy atomic weights of some elements.