History of the Periodic Table Flashcards
What were the two obvious ways to order elements from the early 1800s until recently?
Their physical and chemical properties
Their Relative Atomic Mass (Mass number)
What order were the elements in early periodic tables?
In order of atomic mass NOT atomic number
How did Newlands structure his periodic table?
Law of Octaves
Every 8th element had similar properties therefore he grouped the elements in rows of 7
What was wrong with Newlands’ table?
The pattern broke down on the 3rd row, with the transition metals.
It was because he left no gaps that his work was ignored.
Newlands presented his ideas to the Chemical society in 1865. Why was his work criticised?
1) His groups (columns) contained elements that didn’t have similar properties.
2) He mixed up metals and non-metals
3) He didn’t leave any gaps for elements that hadn’t been discovered yet.
How many elements did Mendeleev know about?
About 50
When did Mendeleev create his table?
1869
What order did Mendeleev put the elements in?
Atomic mass
What did Mendeleev do differently to Newlands? Why was this useful?
He left gaps for undiscovered elements as he predicted new elements. This meant that Mendeleev could put elements with similar properties in the same groups (columns)
What happened to Mendeleev’s table once more elements were discovered.
It was updated, new elements fit in the gaps left by Mendeleev
Why did scientists not like the periodic table? What happened soon after?
Not much evidence to suggest that the order was right
BUT THEN…
Scientists realised the table could be a useful tool for predicting proprieties of elements
Why do modern scientist like the periodic table?
They accept that it’s a very important and useful summary of the structure of atoms
In which century were protons, neutrons and electrons discovered?
19th
