Development of the Periodic Table Flashcards
Before recent times, how were elements categorised?
1) Their physical and chemical properties
2) Their relative atomic mass
Where does the name periodic table come from?
When only relative atomic mass was the only thing people could measure, the known elements were arranged in order of atomic mass. When this was done, a periodic pattern was noticed in the properties of elements - therefore the name periodic table was given to the order of elements.
What was wrong with early periodic tables?
They weren’t complete and elements were placed in the wrong group. This is because elements were placed in order of relative atomic mass and did not take into account of properties.
What did Dmitri Mendeleev do in 1869?
He overcame some of the problems with the early periodic table by taking 50 known elements and arranging them into his Table of Elements with gaps.
What did Mendeleev do with the order of elements in his table?
He put them in order of atomic mass but did switch the order if properties meant it should be changed.
Why were gaps left in the table?
They were left in the table to make sure that elements with similar properties stayed in the same groups. Some of the gaps indicated the existence of undiscovered elements - when they were found they fitted the pattern it helped confirm Mendeleev’s ideas.
What did the discovery of isotopes do with Mendeleev’s ideas?
It confirmed that Mendeleev was correct not to place elements in a strict order of atomic mass but to also take account of their properties.
