The Periodic Table
The arrangement of chemical elements by atomic number that reveals repeating patterns in their properties.
- First published
- 1869
- Elements
- 118 confirmed
Mendeleev's insight
In 1869 Dmitri Mendeleev ordered the known elements and left gaps for ones not yet discovered. Elements later found, such as gallium and germanium, matched his predictions closely.
How it is read
Rows are called periods and columns are called groups. Elements in the same group share similar chemical behaviour because their outer electrons are arranged in similar ways.