the periodic table

Question 1

Dobereiners triads…

Answer 1

In 1817…

• put into groups called triads (each triad contained 3 elements)
• each group of triads had similar properties
• the relative atomic mass in the middle element of each triad was close to the relative atomic masses of the other elements.

Question 2

Newlands octaves…

Answer 2

In 1864…

• he arranged all the known elements at the time into a table in order of relative atomic mass.
• when he did this he discovered that each element had similar properties to an element eight places on.
• his table wasn’t accepted by other scientists because it had two non- metal elements in the same group.

Question 3

Mendeleev’s table…

Answer 3

In 1869…

• he created a periodic table that ordered the elements in relative atomic mass.
• he arranged them so that groups of elements with similar properties fell into vertical columns in his table.
• there were some gaps in his table for undiscovered elements that he predicted were there and he was right!