Atomic Number And The Periodic Table - Periodic Table

Question 1

How were elements arranged in the early 1800s?

Answer 1

By atomic weight.
Table wasn’t complete
Protons neutrons and electrons yet to be discovered

Question 2

How did Mendeleev arrange periodic table in 1869?

Answer 2

Arranged mainly by atomic weight
Sometimes switched positions or left gaps in the table, so he could ensure elements with similar properties stayed in same group
He used the gaps to predict the properties of the yet to be discovered elements

Question 3

How is the modern periodic table organised?

Answer 3

In order of increasing atomic number
Metals on the left, non metals on right
Elements with similar properties are in groups
Group number of an element is the same as the number of outer shell of electrons - besides group 0.
Rows in periodic table are called periods, each new row represents another shell of electrons.