the periodic table information page
The Periodic Table we use today is based on the one devised and published by Dmitri Mendeleev in 1869. Mendeleev found he could arrange the 65 elements, then known in a grid or table, so that each element had:
1. A higher atomic weight than the one on its left. For example, magnesium (atomic weight 24.3) is placed to the right of sodium (atomic weight 23.0). The periodic table we use today is based on the one devised and published by Dmitri Mendeleev in 1869.
23.0 24.3
Na Mg
2. Similar chemical properties to other elements in the same column - in other words similar chemical reactions. Magnesium, for example, is placed in the alkali earths' column:
9.01
Be
24.3
Mg
40.1
Ca
87.6
Sr
Mendeleev realized that the table in front of him lay at the very heart of chemistry. And more than that, Mendeleev saw that his table was incomplete - there were spaces where elements should be, but no-one had discovered them.
1. A higher atomic weight than the one on its left. For example, magnesium (atomic weight 24.3) is placed to the right of sodium (atomic weight 23.0). The periodic table we use today is based on the one devised and published by Dmitri Mendeleev in 1869.
23.0 24.3
Na Mg
2. Similar chemical properties to other elements in the same column - in other words similar chemical reactions. Magnesium, for example, is placed in the alkali earths' column:
9.01
Be
24.3
Mg
40.1
Ca
87.6
Sr
Mendeleev realized that the table in front of him lay at the very heart of chemistry. And more than that, Mendeleev saw that his table was incomplete - there were spaces where elements should be, but no-one had discovered them.