Development of the periodic table

Cards (6)

How were elements arranged in the 1800s
By atomic weight
Why were elements often placed in the wrong group?
Since they were placed in order of atomic weight rather than atomic mass, the elements chemical properties werent taken into account
How did Mendeleev arrange his Periodic table
Ordered elements by increasing atomic weight
Arranged elements that had similar properties into rows and columns
He left gaps
Why did Mendeleev leave gaps
To leave space for undiscovered elements
How did isotopes help validate Mendeleev’s periodic table
Some isotopes had different masses, but the same chemical properties so he was correct in putting them in groups with other elements with similar properties
How are elements arranged in a modern day periodic table
Increasing atomic number
Patterns of chemical and physical properties